WO2011033933A1 - 平均自由行程を測定する装置、真空計、および平均自由行程を測定する方法 - Google Patents
平均自由行程を測定する装置、真空計、および平均自由行程を測定する方法 Download PDFInfo
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- WO2011033933A1 WO2011033933A1 PCT/JP2010/064917 JP2010064917W WO2011033933A1 WO 2011033933 A1 WO2011033933 A1 WO 2011033933A1 JP 2010064917 W JP2010064917 W JP 2010064917W WO 2011033933 A1 WO2011033933 A1 WO 2011033933A1
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- mean free
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L21/00—Vacuum gauges
- G01L21/30—Vacuum gauges by making use of ionisation effects
- G01L21/32—Vacuum gauges by making use of ionisation effects using electric discharge tubes with thermionic cathodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
Definitions
- the present invention relates to an apparatus for measuring a mean free path, a vacuum gauge, and a method for measuring a mean free path.
- Patent Document 2 As a method for realizing such a state, there is a so-called ion sputtering method (see Patent Document 2), in which sputtered particles are ionized by some method and incident perpendicularly to a substrate holder on which the substrate is placed.
- a negative DC bias or RF power is applied to the substrate to generate a negative voltage on the substrate, thereby attracting the ions to the substrate holder.
- the thermal energy of the sputtered particles is considered to be about 0.1 eV at most. Therefore, if there is no collision of ions between the target and the substrate holder, the incident energy is almost perpendicular to the substrate. Will do.
- the region where ions are accelerated is a region called a cathode fall or sheath existing in the vicinity of the cathode. Many of the potential changes occurring during the discharge occur in this portion.
- the thickness depends on the pressure of the discharge space, the power applied to the substrate holder, and the like, but is typically about 10 to 30 mm. Therefore, if ions can pass without colliding with the cathode fall or sheath region, an ion beam having a small divergence angle can be incident on the substrate.
- the mean free path the average distance that the particles can move without colliding. If the mean free path in the actual process gas is known, incident ions with a small divergence angle can be obtained by adjusting the process conditions to make the mean free path longer than the cathode fall or sheath length. I can do it.
- the mean free path is obtained by conversion (see Non-Patent Documents 1 and 2). That is, conventionally, the mean free path is not directly obtained, but indirectly obtained from the temperature, the particle diameter of the gas, and the ion diameter.
- gas number density means the number of molecules per unit volume when the gas is a molecule, and the number of atoms per unit volume when the gas is a monoatomic molecule.
- the mean free path can be used in various fields, not limited to sputtering and dry etching.
- the mean free path can indicate the degree of vacuum.
- the present invention has been made in view of such problems, and the object of the present invention is to provide an apparatus for measuring an average free path capable of accurately and simply measuring an average free path of a charged particle, a vacuum gauge, and an average It is to provide a method for measuring a free path.
- the present invention is an apparatus for measuring the mean free path of charged particles in an atmospheric gas, wherein the generation source for generating the charged particles and the flight distance from the generation source are as follows. A first charged particle number of charged particles having a first flight distance of 0 or more is detected, and a second charged particle number of charged particles having a second flight distance longer than the first flight distance is detected. It is characterized by comprising detection means and calculation means for calculating the mean free path from the ratio of the number of the first and second charged particles.
- the present invention is also a vacuum gauge for measuring a degree of vacuum, wherein a generation source for generating charged particles, and a first of a charged particle having a first flight distance of zero or more from the generation source. Detecting means for detecting the number of charged particles of 1 and detecting the number of charged particles of the second flight distance that is longer than the first flight distance; and the number of the first and second charged particles And calculating means for calculating the mean free path from the ratio.
- the present invention is an apparatus for measuring the mean free path of charged particles in an atmospheric gas, the generation source for generating the charged particles, and the first flight distance having a flight distance of 0 or more from the generation source Detecting means for detecting a first charged particle number of charged particles, and detecting a second charged particle number of charged particles having a second flight distance longer than the first flight distance; Storage means for storing the first and second charged particle numbers.
- the present invention is an apparatus for measuring the mean free path of charged particles in an atmospheric gas, the generation source for generating the charged particles, and the first flight distance having a flight distance of 0 or more from the generation source Detecting means for detecting a first charged particle number of charged particles, and detecting a second charged particle number of charged particles having a second flight distance longer than the first flight distance; And display means for displaying the number of first and second charged particles.
- the present invention detects a first charged particle number of a generation source that generates charged particles and a charged particle that has a first flight distance of zero or more from the generation source.
- a control device for controlling an apparatus comprising a detecting means for detecting a second charged particle number of charged particles having a second flight distance that is longer than a flight distance, wherein the generation source is configured to generate the charged particles.
- the present invention is a method for measuring the mean free path of charged particles in an atmospheric gas, the step of generating the charged particles from a generation source, and a first flight distance of 0 or more from the generation source Detecting a first charged particle number of charged particles that is a flight distance, detecting a second charged particle number of charged particles having a second flight distance that is longer than the first flight distance; And calculating the mean free path from the ratio of the number of second charged particles.
- FIG. 15B is a cross-sectional view taken along line AA ′ of FIG. 15A. It is a block diagram which shows schematic structure of the control system in the apparatus which measures a mean free path based on this invention.
- the mean free path of charged particles such as ions and electrons is directly obtained by using a new principle that has not existed before. That is, the basic principle of the new principle characteristic of the present invention is that neutral particles in which charged particles (ions and electrons) flying at two different distances (the shorter distance includes distance 0) are atmospheric gases and The amount of attenuation due to the collision is measured, and the average free path of charged particles (the average value of the distance traveled by the charged particles without collision) is calculated from the ratio. This attenuation is the same exponential phenomenon as the attenuation of the radiation element, and the abundance will always become a certain ratio as time advances (flight distance).
- the half-life is the time until the abundance of radiation elements is halved, but the mean free path is the flight distance of 1 / e (0.37 times) in the mean free path. Since the attenuation is an exponential function in this way, the attenuation intensity (that is, the mean free path) can be calculated mathematically when the attenuation amounts at two different flight distances are known.
- the mean free path of charged particles (ions and electrons) in neutral molecules (in a predetermined gas atmosphere) is obtained.
- the mean free path of ions in the gas atmosphere (neutral molecules) is substantially equal to the mean free path of neutral molecules corresponding to the ions in the gas atmosphere (neutral molecules). Therefore, the mean free path of the predetermined ions in the predetermined gas atmosphere (neutral molecules) is obtained, thereby obtaining the mean freeness of the neutral molecules corresponding to the predetermined ions in the predetermined gas atmosphere (neutral molecules).
- the “neutral molecule corresponding to the ion” is a neutral molecule before the ion is ionized.
- a generation source for example, an ion source or an electron source
- the shorter distance includes a distance 0 from the generation source.
- Two collectors are installed on the flight axis of charged particles. At this time, when two collectors are installed on the flight axis of the same charged particle, the closer collector is configured to supplement a part of incident charged particles such as a mesh shape and transmit the other part. Some charged particles pass through it to reach the far collector.
- the mesh transmittance and flight distance can be any value as long as the values are known accurately.
- the number of charged particles is measured with the two collectors.
- the number of generation sources may be as many as the number of collectors, or one generation source is provided on the rotation stage, and the rotation stage is rotated so that the charged particles from the generation source on the rotation stage are respectively supplied. You may make it input into a collector. In this case, “calibration without attenuation” described later may be performed.
- the two collectors are provided on the flight axis of the same charged particle, and charged particles in each of at least two collectors provided at different distances from the source. It is important to measure the number. This is because the present invention essentially uses the ratio of the number of charged particles in order to exclude factors such as fluctuations in the amount of charged particles generated at the generation source. At least two collectors are provided at different distances.
- the number of collectors is not limited to two, and may be three or more (see first to ninth embodiments described later). Furthermore, the number of collectors may be one as long as it can measure at least two flight distances of charged particles (see the tenth embodiment described later).
- the present invention it is essential to obtain the mean free path by using the ratio of the number of charged particles.
- the first charge of charged particles that have flew for a first flight distance (a distance of 0 or more).
- the number of particles is detected, and the second number of charged particles that have traveled by a second flight distance longer than the first flight distance is detected. Therefore, any number and structure of collectors may be used as long as the number of first and second charged particles can be measured.
- the new principle does not require an absolute value of attenuation, and only the ratio of both is required. Therefore, no matter how much the amount of charged particles in the source of the original charged particles changes, detection by contamination and deformation of the electrode These are irrelevant even if there are side fluctuations. That is, background and fluctuation / disturbance elements are almost completely eliminated.
- the detection means is configured to detect charged particles having a flight distance of two.
- the detection unit may be configured to detect a charged particle having a first flight distance and a charged particle having a second flight distance with a single collector.
- the mean free path is directly determined by the distance to the first collector) and the second flight distance (eg, the distance from the source to the second collector). Therefore, since various fluctuation components are not included in the parameters for calculating the mean free path, the mean free path can be accurately obtained. Furthermore, since a separate measurement (mass analysis) or the like is not required for obtaining the mean free path as in the prior art, the mean free path can be easily obtained.
- the “first collector” refers to detecting a charged particle having a first flight distance of zero or more from a charged particle generation source such as an ion source among two collectors. Is a collector for. Therefore, an internal collector provided inside the generation source can also be included in the first collector.
- the “second collector” is a collector for detecting charged particles having a second flight distance that is longer than the first flight distance from the generation source, The distance from the source is a collector farther than the first collector.
- internal collector refers to a collector provided inside a source of charged particles such as an ion source. Therefore, the collector provided outside the generation source is also referred to as “external collector”.
- the collector on the source side (including the internal collector) is the first collector, and the other collector is the second collector.
- the collector on the source side including the internal collector
- the other collector is the second collector.
- one of the three or more collectors including the internal collector, except for the collector farthest from the source
- the first collector is the first collector
- the first collector is the first collector
- the mean free path can be directly and accurately obtained, more accurate mean free path values can be applied in various fields using the mean free path. For example, in sputtering or dry etching, it is possible to accurately and easily adjust the incidence of an ion beam having a small divergence angle on a substrate or an etching surface. Further, for example, it can be applied to the field of measuring the degree of vacuum.
- the degree of vacuum can be indicated by three quantities: “gas number density”, “pressure”, and “mean free path”.
- the degree of vacuum is obtained by measuring the gas number density with an ion gauge (ionization vacuum gauge) or the like, or by measuring the pressure (force that pushes the wall of a unit area) with a diaphragm vacuum gauge or the like.
- the ion gauge collides high-speed electrons with neutral molecules, which are atmospheric gases, blows off outer shell electrons to ionize them, collects the ions in a collector (detector), and measures the amount of ions. Since the amount of ions is proportional to the gas number density of the atmospheric gas, specify the energy and amount of electrons, the shape and potential of the electrode, and obtain the relationship (converted value) between the amount of ions once measured and the gas number density. In this case, the gas number density can be calculated from the actually measured ion amount.
- the conversion value between the ion amount and the gas number density is generally referred to as sensitivity.
- the diaphragm vacuum gauge is electrically (assuming the magnitude of electric capacity) that the diaphragm existing between the atmosphere gas and a sufficiently good vacuum area provided inside is deformed by the force (pressure) of the atmosphere gas. measure. Since the amount of deformation depends on the pressure of the atmospheric gas, the pressure can be calculated from the amount of deformation once a conversion value or conversion formula is obtained in the same manner. As described above, the measurement principle is different, and the applicable vacuum range is different. However, in both cases, an amount (ion amount / deformation amount) that depends on the degree of vacuum (gas number density / pressure) depends on a conversion value or a conversion formula. The point of calculating the degree of vacuum is the same.
- the mean free path is obtained from the ratio of the number of charged particles detected by at least two collectors and the distance from the source to the collector as the flight distance of the charged particles.
- the mean free path can be calculated in a form that completely eliminates ground and fluctuation / disturbance elements. Since the mean free path indicates the degree of vacuum, according to the present invention, the degree of vacuum can be accurately obtained by excluding background and fluctuation / disturbance elements.
- the accuracy starts to drop at 1 Pa or more due to the influence of space charge, and the measurement limit is about 10 Pa.
- the measurement limit is about 10 Pa.
- the accuracy starts to decrease at 1 Pa or less, and about 0.1 Pa is the measurement limit. In either case, the accuracy is poor at a vacuum level of about 1 Pa, which is frequently used in sputtering and dry etching. Therefore, a vacuum gauge that can accurately measure the vacuum level in this region is strongly desired.
- the mean free path as the degree of vacuum is directly obtained regardless of the space charge, and further without using the diaphragm. Process). Therefore, it can be measured well even at a vacuum degree of around 1 Pa.
- both the conventional ion gauge and the diaphragm vacuum gauge convert the amount (ion amount / deformation amount) proportional to the degree of vacuum (density gas number density / pressure) into the degree of vacuum using a conversion value or conversion formula.
- Two measures were required to ensure the accuracy: correctly measuring the absolute value of the quantity and not changing the conversion value or conversion formula.
- the new measurement principle characteristic of the present invention does not require these two, and it is possible to obtain the absolute value of the degree of vacuum (mean free path) by eliminating the disturbance element.
- vacuum indicating the level of vacuum and “pressure”, which is one expression of vacuum, are often used interchangeably, but in the present specification, these are strictly distinguished.
- low pressure low pressure
- high vacuum high pressure
- low vacuum low vacuum
- low vacuum low vacuum
- low vacuum low vacuum
- low vacuum low vacuum
- low vacuum low vacuum
- high pressure low vacuum
- low vacuum low vacuum
- low vacuum low vacuum
- low vacuum low vacuum
- low vacuum low vacuum
- low vacuum low vacuum
- high pressure high pressure
- FIG. 1A is a schematic diagram for explaining the principle for obtaining the mean free path of the present invention in the case of an ion source that does not depend on the degree of vacuum.
- a collector 12a as a first collector is disposed at a distance L1 from the ion source 11a
- a collector 12b as a second collector is disposed at a distance L2 (L2> L1) from the ion source 11b.
- L1 distance from the ion source 11a
- L2 L1> L1
- FIG. 1A is a conceptual diagram showing the principle of the present invention.
- Ions output from the ion source 11a fly by a flight distance L1 and input to the collector 12a.
- the collector 12a calculates the number of ions I L1 after attenuation. detect, and ions that are output from the ion source 11b is input to the collector 12b flying by flight distance L2, the collector 12b is an indication to detect the number of ions I L2 of the attenuated. Therefore, the collectors 12a and 12b may be arranged on the flight axis of the same ion within the same region (with the same degree of vacuum and the same temperature) (in this case, the ion source 11a and the ion source).
- collectors 12a and 12b may be arranged on the flight axes of different ions as shown in FIG. 1A. However, in the latter case, “calibration without attenuation” described later is preferably performed.
- I L1 I 0 ⁇ exp ( ⁇ L1 / ⁇ ) (1)
- I L2 I 0 ⁇ exp ( ⁇ L2 / ⁇ ) (2)
- ⁇ ⁇ L1 / In (I L1 / I 0 ) (3)
- ⁇ ⁇ L2 / In (I L2 / I 0 ) (4)
- the mean free path can be obtained by comparing the number of ions after attenuation in the two collectors. Since equation (5) is independent of I 0 , highly accurate measurement is expected. That is, when using equation (5), even if there is an undesirable fluctuation in the ion source (even if I 0 is unexpectedly fluctuated), it is not included in the parameter for calculating the mean free path. An accurate mean free path can be obtained.
- reference numeral 13 is a graph showing the relationship between the number of ions IL1 when the flight distance is short and the degree of vacuum (mean free path), and reference numeral 14 is the number of ions I when the flight distance is long. It is a graph which shows the relationship between L2 and a vacuum degree (mean free path).
- the number of ions is constant, that is, not dependent on the gas number density, but when the mean free path is shorter than the flight distance (FIG. 1B).
- the number of ions after flight decreases (decays).
- the degree of vacuum is changed from a good state to a bad state (moving from the left to the right side of the horizontal axis)
- the attenuation starts (to be exact, the attenuation starts to become significant). It will be when it is shortened to the same extent.
- FIG. 2A is a schematic diagram for explaining the principle of obtaining the mean free path of the present invention in the case of an ion source whose ion current depends on the degree of vacuum
- FIG. 2B is a diagram showing the number of ions by flight in FIG. 2A. It is a figure for demonstrating the condition which attenuates.
- a vacuum degree-dependent ion source 21a includes a grid 22a and a filament 23a, and a collector 24a serving as a first collector is disposed at a distance L1 from the ion source 21a.
- the ion beam 25 output from the ion source 21a is input to the collector 24a.
- the vacuum degree-dependent ion source 21b includes a grid 22b and a filament 23b, and a collector 24b as a second collector is disposed at a distance L2 from the ion source 21b.
- the ion beam 25 output from the ion source 21b is input to the collector 24b.
- FIG. 2A is a conceptual diagram showing the principle of the present invention in the same manner as FIG. 1A. Therefore, the collectors 24a and 24b may be arranged on the flight axis of the same ion within the same region (with the same degree of vacuum and the same temperature) (in this case, the ion source 21a and the ion source). 21b is a single ion source), and collectors 24a and 24b may be arranged on the flight axes of different ions as shown in FIG. 2A. However, in the latter case, “calibration without attenuation” described later is preferably performed.
- reference numeral 26 is a graph showing the relationship between the ion current of the ion source and the degree of vacuum before attenuation, that is, assuming no collision
- reference numeral 27 is the ion current after attenuation
- It is a graph which shows the relationship between the ion current when the flight distance is short (the ion current detected by the collector 24a) and the degree of vacuum
- Reference numeral 28 is the ion current after attenuation, and the flight distance is long. It is a graph which shows the relationship between ion current (ion current detected by the collector 24b) and a vacuum degree.
- the ion source 21a includes a grid 22a having a cylindrical shape that can transmit electrons, such as a lattice, and a filament 23a that emits thermal electrons when heated.
- the voltage is applied to the grid 22a at + 100V and the filament 23a at about + 30V. Electrons emitted from the filament 23a travel toward the grid 22a, but most of the electrons enter the grid 22a, where they collide with the atmospheric gas and generate positively charged ions.
- ions are generated at substantially the potential (+100 V) of the grid 22a, the ions travel toward the collector 24a having the ground potential, and the number of ions (ion current) generated by the current flowing through the collector 24a is obtained. The same applies to the ion source 21b.
- FIG. 3 is a diagram for explaining measurement of the number of ions I 0 (ion current) before attenuation (ion source).
- the internal collector 31 is inserted into the grid 22a (22b), electrons are emitted from the filament 23a (23b) to generate ions, and the ions are measured by the internal collector 31. , The number of ions I 0 can be obtained.
- a collector (external collector) is installed at a position away from the grids 22a and 22b by a certain distance, and the ion current is measured. With this configuration, the configuration shown in FIG. 2A is obtained.
- Method for obtaining first mean free path A method for obtaining the mean free path using an ion source having a degree of vacuum dependence is shown. However, for simplicity, it is assumed that the following three points are satisfied.
- ⁇ The ion source used for measurement is located in the region of the same degree of vacuum and the same temperature.
- ⁇ The ion source used for measurement generates the same number of ions.
- ⁇ The ion detection efficiency of each collector (detector) is equal.
- FIG. 4 is the same as the graph of FIG. 2B, but specific numbers are shown.
- the horizontal axis represents the degree of vacuum and is expressed in Pa (about 100,000 Pa is atmospheric pressure).
- the vertical axis is the ion current, but in arbitrary units.
- FIG. 4 also shows the ion current attenuated by each flight in FIG. 2A, where the short flight distance L1 is 8 mm and the long flight distance L2 is 60 mm. Further, the ion current before attenuation is shown by a straight line. Gas is a N 2.
- reference numeral 41 is a graph showing the relationship between the ion current detected by the internal collector 31 of the ion source and the degree of vacuum before attenuation.
- the degree of vacuum is line A (0.1 Pa).
- the ion current at this degree of vacuum is 1.1 (arbitrary unit; the same applies hereinafter) before attenuation by the internal collector 31 from FIG. 4, and is 0.4 after attenuation of ions by the collector 24b in 60 mm flight.
- the mean free path is calculated to be 60 mm (in this case, since the mean free path and the flight distance are exactly the same, the ion current is attenuated by 1 / e: 0.37 times).
- the degree of vacuum is a line D (2 Pa).
- the ion current at this degree of vacuum is 25 before attenuation by the internal collector 31 and 1.8 after attenuation by 6 mm flight of ions by the collector 24a.
- the mean free path is calculated to be 3 mm.
- the mean free path is calculated to be 30 mm.
- the dotted line 44 in FIG. 4 is an attenuation curve at a flight distance of 52 mm, and the same value is obtained even if this and equation (3) are used (mathematical equivalent).
- the mean free path differs between neutral molecules and between ions / neutral molecules, but also changes depending on the kinetic energy (velocity) of ions. It can be considered practically the same. However, since effective diameters of electrons described later are significantly different, the mean free path of electrons is 5.6 times.
- a composite ion source disclosed in Patent Document 3 is applicable.
- This composite ion source has the same basic structure as an ordinary BA gauge, and includes a filament that emits thermal electrons, a grid that draws electrons and generates ions inside, and a collector into which the generated ions flow. .
- the length of the collector is almost equal to the grid length (axial length) (4/5 or more), but in the case of a composite ion source, the length of the collector is set. Is shorter than the length of the grid, preferably half (1/2).
- These (collector length) structures in a normal B-A gauge aim to collect as many ions generated in the grid as possible, but are not necessarily indispensable as the characteristics of the vacuum gauge. Even with a composite ion source with half the collector, the sensitivity (converted value) is about half, but sufficient practical performance as a vacuum gauge can be secured.
- an ion source that is, a device that extracts and uses ions
- the composite ion source ensures sufficient practical performance.
- an ion source having no collector at all referred to as a BA type ion source
- a composite ion source has a performance as an ion source (ion amount, etc.). It has been confirmed that it sufficiently functions as an ion source.
- the filament length is approximately equal to the grid length (axial length), so that a substantially uniform amount of electrons are incident inside the grid in the entire axial direction, and ions are also almost uniform throughout the axial direction. Generate.
- the collector length is approximately equal to the grid length, almost all of the generated ions flow into the collector.
- the length of the collector is only half of the grid, only about half of the ions are collected in the collector, and the other ions are emitted outside the grid in the axial direction.
- the performance of the composite ion source is substantially the same as the conventional ion source except that the sensitivity (converted value) is half that of the conventional vacuum gauge, and the ion source sufficiently functions as an ion source. Since almost the same amount of ions as that measured by the internal collector are emitted to the outside as a beam, the internal current I 0 before attenuation can be measured by the internal collector. However, since it is not exactly the same amount, it is desirable to correct this difference by “calibration without attenuation” described later. In the first to third embodiments (FIGS. 5 to 7), a composite ion source is employed.
- the first collector Permeation of the first collector (collector 12a, 24a, etc.)
- This measurement method always requires two or more collectors (detectors), but it is not practical to prepare an ion source (ion beam) for each.
- two collectors are installed in series in one ion source (ion beam) (two collectors are arranged on the flight axis of the same ion), and a part of the first collector close to the ion source is used.
- the remaining ions may be transmitted as they are and proceed to the second collector located farther than the first collector.
- the first collector has a mesh shape, a slit shape, or a structure provided with at least one small window.
- the first collector may be a thinned conductive member (for example, a silicon thin film). Under predetermined conditions, when charged particles enter the conductive thin film, a part of the charged particles is captured by the conductive thin film and the other part is transmitted as it is.
- any member can be used as the transmissive first collector as long as it is a member that can detect a part of incident charged particles and transmit the other part. Also good. In calculating the mean free path, the original current is calibrated based on the detection rate of ions by the first collector.
- the respective detection efficiencies may be obtained in advance and the measured values may be calibrated with this.
- the ion current ratio of both collectors when the degree of vacuum is sufficiently good (no attenuation) is obtained, these become the original detection efficiencies, so it is effective to divide the measured value by this value It becomes. For example, it is assumed that 40% of ions are measured by the first collector, and the remaining 60% of ions are transmitted as they are to reach the second collector and are measured there. In this configuration, when there is no attenuation (collision with the atmospheric gas), the ion current ratio between the first collector and the second collector is naturally 4 to 6.
- I L1 vs I L2 is (d / a) vs (e / b).
- the ion currents at the respective collectors are measured in a state of good vacuum so that attenuation can be ignored, and the value is set as an initial value (value without attenuation). Then, in actual measurement, calculation may be performed by normalizing each actually measured ion current to a value obtained by dividing by this initial value.
- I L1 vs. I L2 becomes (d / a) vs. (e / b).
- the calibration without attenuation means that the ratio of the number of charged particles detected in the first collector and the second collector in the first vacuum state (for example, in a good vacuum state) Calibrating the ratio of the number of charged particles detected at the first collector and the second collector at a vacuum level (for example, a vacuum level worse than the first vacuum level).
- this 52mm difference in flight distance
- this 52mm should be about 0.2 to 4 times the mean free path, so from 5 times 52mm (0.2 times reciprocal) to 0.25 times (4 times reciprocal)
- the vacuum degree of the mean free path from 260 mm to 13 mm can be applied. In the pressure display, this is 0.03 Pa to 0.5 Pa.
- the difference in flight distance will be 8mm. As above, from 5 times to 0.25 times, that is, from 40mm. A vacuum degree with an average free path up to 2 mm is applicable. In the pressure display, this is from 0.15 Pa to 3 Pa.
- Vacuum gauge calibration The range indicated by the vacuum degree range in the above item 11) is a case where the mean free path is directly measured, but if used in combination with an ion gauge function in a composite ion source, the range of vacuum degree should be further widened. I can do it. In other words, it is possible to measure a very accurate degree of vacuum in a normal ion gauge measurement range, that is, in a wide range from about 1 Pa to 10 ⁇ 8 Pa. As shown in item 8) above, the compound ion source has the same functions and performance as the conventional ion gauge (BA gauge) except that the sensitivity (converted value) is half. .
- BA gauge conventional ion gauge
- the ion gauge (BA gauge) originally has excellent performance of maintaining linearity over a wide range of several digits or more, sensitivity (converted value), that is, the absolute value of the signal amount Has the disadvantage of being easy to change.
- the line of 45 degrees to the right of the graph 41 indicating “ion current before decay (ion source)” corresponds to the vacuum degree display of the ion gauge, but the linearity is good when the line is a straight line.
- the fact that the sensitivity (converted value) is likely to change means that the vertical position of the entire line is likely to shift (Figure 4 is a log-log graph, so the vertical position is shifted, but in the normal graph, the linearity is Changing means that the slope changes).
- the method according to the present invention has a narrow measurement range, the degree of vacuum obtained is very accurate, so the conversion value that is the correct sensitivity (conversion value) of the ion gauge is clarified compared with the value of the ion gauge measured at the same time. I can do it. That is, the vertical position of the entire line can be set correctly.
- vacuum gauge calibration This process of calibrating the sensitivity (converted value) of other gauges (gauges) will be referred to as “vacuum gauge calibration”.
- the degree of vacuum does not need to be known, and an arbitrary degree of vacuum may be used as long as attenuation occurs.
- the type of gas must be known. That is, if the degree of vacuum is in the range shown in the above item 11), the mean free path can be accurately calculated, and the value can be used for calibration.
- the adjustment means may be adjusted so that the display of another vacuum gauge to be calibrated displays 1 (Pa). In this case, accuracy of the flight distance is required, but this can be easily realized. From this point on, it is done in the same way as normal calibration.
- the calibration according to the present invention does not require a special device and can be performed in a short time. Therefore, vacuum gauge calibration can be automatically performed during actual measurement. That is, in most processes such as sputtering, the degree of vacuum is such that attenuation is caused by a predetermined gas, and calibration is performed at that time.
- Countermeasures for stray ions and stray electrons Ions and electrons that collide with the atmospheric gas (neutral molecules) do not disappear, but simply lose kinetic energy, so they remain and float in the flight space as stray ions and stray electrons. Therefore, if stray charged particles such as stray ions and stray electrons are not quickly removed, they may reach the collector and cause an error in charged particle amount measurement.
- One of the countermeasures is mechanical: charged particles unrelated to measurement are not allowed to enter the flight area, charged particles that have lost energy are blocked in front of the collector, ground potential (or slightly negative potential) A stray charged particle is absorbed by installing a plate in the vicinity of the flight region. The mechanical method is adopted in the second, fourth to eighth embodiments (FIGS. 5, 9, 10, 11, and 13).
- Ion current is measured using a lock-in (modulation-synchronous) amplifier instead of the usual direct current (DC). Since only the alternating current component that is modulated (intermittent) and is synchronized with the generation of ions (electrons) is detected by a lock-in (modulation synchronization type) amplifier, only ions (electrons) that have not collided with the atmospheric gas must be detected (Details will be described in the third embodiment).
- the lock-in (modulation synchronization type) amplifier method is effective when an absorbing plate cannot be installed, or when a certain disturbing current enters other than the colliding ions (electrons).
- the electrical method is adopted in the third, ninth, and tenth embodiments (FIGS. 7, 8, 15, and 16).
- Control Unit A device 1007 for measuring the mean free path can incorporate the control unit 1000 shown in FIG. Further, the control unit may be connected through an interface.
- FIG. 16 is a block diagram showing a schematic configuration of a control system according to an embodiment of the present invention.
- reference numeral 1000 denotes a control unit as control means for controlling the entire apparatus 1007.
- the control unit 1000 includes a CPU 1001 that executes processing operations such as various calculations, control, and determination, and a ROM 1002 that stores various control programs executed by the CPU 1001.
- the control unit 1000 also includes a RAM 1003 that temporarily stores data during processing operations of the CPU 1001, input data, and the like, and a nonvolatile memory 1004 such as a flash memory and an SRAM.
- control unit 1000 includes an input operation unit 1005 including a keyboard or various switches for inputting predetermined commands or data, and a display unit 1006 for performing various displays including the input / setting state of the device 1007. (For example, a display) is connected.
- input operation unit 1005 including a keyboard or various switches for inputting predetermined commands or data
- display unit 1006 for performing various displays including the input / setting state of the device 1007. (For example, a display) is connected.
- FIG. 5 is a diagram showing an apparatus 1007 for measuring the mean free path according to the first embodiment of the present invention, in which a composite ion source and a transmission type collector are used.
- the entire apparatus 1007 shown in FIG. 5 is installed in the atmospheric gas to be measured.
- the ammeter shown in the figure is schematic and is actually disposed outside the atmospheric gas.
- each electrode is attached and fixed by a method well known as a vacuum gauge, and the connected wiring is conducted to the atmosphere side.
- each electrode is screwed to an insulating stone (ceramic or the like), and an electrically welded wiring (nickel wire or the like) extends to a control device on the atmosphere side through a glass-sealed introduction terminal.
- a device 1007 for measuring the mean free path as a vacuum gauge includes a composite ion source 100, a transmission collector 202, and a collector 203.
- Collectors 202 and 203 are disposed on the ion flight axis of ions 110 output from ion source 100. Further, the collector 202 is provided so that the distance from the ion emission surface of the ion source 100 to the ion detection surface of the collector 202 is La. Therefore, the collector 202 detects ions having a flight distance La from the ion source 100. Further, the collector 203 is provided so that the distance from the ion emission surface of the ion source 100 to the ion detection surface of the collector 203 is Lb. Therefore, the collector 203 detects ions at a flight distance Lb from the ion source 100.
- the composite ion source 100 is a cylindrical type (about ⁇ 10 mm, length about 30 mm) and a grid 102 (grid spacing 3 mm, transmission rate about 95%), etc., and a grid 102 with a shape of about 0.2 mm. It has a filament 101 that is heated to 1800 ° C. or more by a wire and emits thermoelectrons, and an internal collector 201 made of W wire having a diameter of about 0.1 mm.
- the grid 102 is applied with a voltage of about +100 V
- the filament 101 is applied with a voltage of about +30 V
- the internal collector 201 is at ground potential (ground / ground potential, specifically 0 V, the base potential of the whole vacuum gauge). Electrons emitted from the filament 101 travel toward the grid 102, but most of the electrons penetrate into the grid 102, where they collide with the atmospheric gas and generate positively charged ions 110. Since the ions 110 are generated almost at the potential of the grid 102 (+100 V), a part of the ions 110 flows into the internal collector 201 at the ground potential. In this way, the internal collector 201 detects the number of ions I c is the number of ions before attenuation.
- the length of the internal collector 201 is about half the axial distance of the grid 102, and the other end of the grid 102 (the side opposite to the collectors 202 and 203) is open, so it does not flow into the internal collector 201.
- Other ions 110 are ejected out of the ion source 100 and travel toward the ground potential collector 202.
- the ions 110 that collide with the atmospheric gas (neutral molecules) while flying up to the collector 202 lose their kinetic energy and do not reach the collector 202, but some ions 110 reach the collector 202 without colliding with the ions. Measured as current. That is, the collector 202 detects the flight distance L1 flight attenuated ion number I a.
- the collector 202 Since the collector 202 is a transmission type formed in a mesh shape, a part of the ions 110 that have reached the position of the collector 202 proceed toward the collector 203 as they are. Even between the collector 202 and the collector 203, the ions 110 colliding with the atmospheric gas do not reach the collector 203, but some ions 110 reach the collector 203 without colliding and are measured as an ion current. That is, the collector 203 detects the flight distance L2 flight attenuated ion number I b.
- the collector 202 has a mesh interval of 0.3 mm and a transmittance of about 50%.
- a mesh shape such as SUS is suitable.
- the collector 203 is a simple metal plate (plate) made of SUS or the like.
- the distance La between the ion source 100 and the collector 202 is 8 mm so that the vacuum level of about 1 Pa can be measured.
- the distance Lb between 100 and the collector 203 is 60 mm. Since this distance error directly becomes an error in the measurement result, it is important that the distance is accurate and does not change over a long period of time.
- the values of the distance La and the distance Lb are stored in the nonvolatile memory 1004. Accordingly, the nonvolatile memory 1004 holds that the distance La is 8 mm and the distance Lb is 60 mm.
- the ion current and the ion beam diameter are not directly related to the measurement result and are arbitrary, the ion current is approximately 1 ⁇ A (10 ⁇ 6 A), the ion energy is approximately 100 eV, and the ion beam diameter is approximately several mm.
- the current measurement is a normal direct current (DC) measurement, and it is sufficient to detect about 1 nA (10 ⁇ 9 A) to 1 ⁇ A with a response speed of just over 0.1 seconds.
- DC direct current
- the internal collector 201 wants to measure to a better degree of vacuum as a BA gauge, it is desirable that it can measure up to 1 pA ( 10-12 A) even if the response is slow.
- the ion current at each collector is set as an initial value without attenuation. Then, each measured ion current is normalized to a value divided by this initial value and used for calculation. That is, in the measurement for calibration without attenuation, the internal collector 201 detects the number of ions I c ′, the collector 202 detects the number of ions I a ′, and the collector 203 detects the number of ions I b ′.
- the detected number of ions I a ′, number of ions I b ′, and number of ions I c ′ are respectively stored in the nonvolatile memory 1004. Therefore, when performing calibration without attenuation, the control unit 1000 appropriately reads out the number of ions I a ′, the number of ions I b ′, and the number of ions I c ′ as initial values stored in the nonvolatile memory 1004 and reads the readings. Normalize the measured value by dividing it by the initial value, and perform calibration without attenuation.
- the basic procedure for measuring mean free path is as follows. First, the filament 101 is heated and set so that electrons reaching the grid have an appropriate value (it is not always necessary to know this value accurately, and it is not necessary to set it to a strictly constant value). That is, the control unit 1000 controls the apparatus 1007 so that the ions 110 are generated from the ion source 100. Next, the amount of each ion flowing into the internal collector 201, the collector 202, and the collector 203 (the number of ions I c , the number of ions I a , and the number of ions I b ) is measured.
- the control unit 1000 controls the device 1007 so that the internal collector 201, the collector 202, and the collector 203 detect ions, and the detected number of ions I c , number of ions I a , and number of ions I b are set in the device. Obtained from 1007 and stored in the RAM 1003. Finally, using the obtained number of ions I c , number of ions I a , and number of ions I b as appropriate, the mean free path is calculated using equations (3) to (5), of which the ratio of the amount of ions is 1.2. If it is within the range of 100 times to 100 times, it is a definite value. That is, the control unit 1000 reads information according to an equation used for calculating the mean free path and performs calculation.
- the control unit 1000 reads the distance La from the nonvolatile memory 1004, reads the number of ions I c and I a from the RAM 1003, and calculates the mean free path from the read value according to the equation (3).
- the control unit 1000 reads the distance Lb from the nonvolatile memory 1004, reads the number of ions I c and I b from the RAM 1003, and calculates the mean free path from the read value according to the equation (4).
- the first collector becomes the collector 202
- the second collector becomes the collector 203
- the first collector becomes the internal collector 201
- the second collector There is a pattern B in which the collector becomes the collector 202.
- the control unit 1000 reads the distances La and Lb from the nonvolatile memory 1004, reads the numbers of ions I a and I b from the RAM 1003, and calculates the mean free path from the read values according to the equation (5).
- the control unit 1000 reads the distances Lc and La from the nonvolatile memory 1004, reads the ion numbers I c and I a from the RAM 1003, and calculates the mean free path from the read values according to the equation (5).
- control unit 1000 performs the calculation by appropriately selecting and reading each distance and the number of ions according to the formula used for calculation (that is, according to the formula set when used for calculation). Note that the user can set the formula to be used via the input operation unit 1005.
- control unit 1000 can perform calibration without attenuation when obtaining the mean free path.
- control unit 1000 When performing calibration without attenuation, the control unit 1000 appropriately reads out the number of ions I a ′, the number of ions I b ′, and the number of ions I c ′ as initial values from the nonvolatile memory 1004 according to the formula used, Calibration without attenuation can be performed using the read values.
- the control unit 1000 can cause the display unit 1006 to display the mean free path obtained by the calculation. Thus, by displaying, the user can know the current degree of vacuum.
- control unit 1000 may calculate the pressure corresponding to the mean free path from the equation (7) based on the obtained mean free path.
- the apparatus 1007 is provided with a thermometer as temperature measuring means for measuring the temperature of the measurement region of the apparatus 1007, and the temperature of the measurement system of the apparatus 1007 is measured.
- the control unit 1000 can convert the directly obtained mean free path into pressure, and display the converted pressure on the display unit 1006. If the gas component is not known and there is no mass spectrometer, it is calculated with the diameter of N2 and set to the pressure value converted to N2 (this pressure value converted to N2 is a method widely used in ion gauges) ).
- the mean free path is calculated by the control unit 1000, but may be performed by an arithmetic device (for example, a computer, a scientific calculator, etc.) separate from the control unit 1000. That is, in the present invention, it is important to obtain the mean free path using the ratio, and for this purpose, at least two collectors having different distances from the ion source are used, and the number of ions detected by these collectors is used. It is essential to obtain the mean free path by any one of the formulas (3) to (5). Therefore, it does not matter where the calculation for obtaining the mean free path is performed.
- an arithmetic device for example, a computer, a scientific calculator, etc.
- distances La, Lb, and Lc which are distances between the ion source 100 and each collector, are known.
- the numbers of ions I a , I b , and I c detected by each collector are held in a storage unit such as a RAM 1003. Therefore, when the control unit 1000 obtains the mean free path, the calculation may be performed as described above. That is, the control unit 1000 acquires the distances La, Lb, Lc and the numbers of ions I a , I b , I c necessary for calculating the mean free path from the storage unit, and any one of the expressions (3) to (5) Do the calculation of the formula.
- control unit 1000 when the control unit 1000 is connected to the computer and the control unit 1000 via a network, the control unit 1000 is detected by each collector stored in the RAM 1003.
- Information indicating the numbers of ions I a , I b , and I c and information indicating the distances La, Lb, and Lc stored in the nonvolatile memory 1004 may be transmitted.
- the computer acquires the information through a network interface or the like. Next, the computer can calculate the mean free path by performing the same calculation as that of the control unit 1000 using each acquired information.
- the control unit 1000 When the computer is not connected to the control unit 1000 via a network, the control unit 1000 stores the number of ions I a , I b , I c detected by each collector, and nonvolatile data stored in the RAM 1003.
- the distances La, Lb, and Lc stored in the memory 1004 may be displayed on the display unit 1006. By displaying in this way, the user inputs each displayed information into a computer separate from the control unit 1000 using input means such as a keyboard, and any one of the equations (3) to (5) is input to the computer. You just have to calculate that.
- the separate computer obtains the distances La, Lb, Lc and the numbers of ions I a , I b , I c necessary for calculating the mean free path by the user input by the input means, and the equation (3) Calculate one of the formulas (5) to (5).
- the user can obtain the mean free path by performing any one of the expressions (3) to (5) using a scientific calculator based on the displayed information.
- the scientific calculator obtains the distances La, Lb, Lc and the numbers of ions I a , I b , I c necessary for calculating the mean free path by the user input using the numeric keypad of the scientific calculator, and formula (3) ) To (5) is calculated.
- the number of ions I a , I b , and I c detected by each collector is acquired by the apparatus configuration characteristic to the present embodiment as shown in FIG. 5 and the number of ions is stored. It is memorized in the means. Then, by appropriately reading out the stored number of ions and performing the predetermined processing as described above, the equations (3) to (5) can be calculated, and the mean free path can be obtained accurately and easily. Can do.
- the number of detected ions may be displayed on an ammeter connected to each collector in FIG.
- the user inputs the value displayed on the ammeter and the flight distance of ions corresponding to the value to the control unit 1000 via the input operation unit 1005, and further instructs the calculation of the mean free path. input.
- the control unit 1000 acquires the flight distance and the number of ions by these user inputs, and calculates the mean free path by any one of the equations (3) to (5) according to the above calculation instructions.
- the user may input the value displayed on the ammeter into the scientific calculator.
- the scientific calculator obtains the flight distance of ions and the number of ions after attenuation, and the scientific calculator can perform any of the equations (3) to (5). .
- the ion gauge since the composite ion source 100 is used, the ion gauge has a function of measuring the degree of vacuum in a wide measurement range. Therefore, if “vacuum gauge calibration” is performed to calibrate the sensitivity (converted value) of the vacuum gauge by measuring the vacuum degree by the ion gauge function simultaneously with the measurement of the mean free path, the measurement range of the ion gauge, that is, 1 Pa to 10 ⁇ 8. Extremely accurate vacuum measurement can be performed in a wide range up to about Pa. In “Vacuum gauge calibration”, the vacuum is maintained at such a level that attenuation is caused by a known gas type, and the mean free path is measured by the above method and the degree of vacuum (pressure) is measured by the ion gauge function. 1000 calibrates the sensitivity (converted value) of the ion gauge function by comparing the two according to equation (7).
- the degree of vacuum for calibration may be any (unknown) value as long as the mean free path can be measured.
- the simplification is realized by using a composite ion source and a transmission type collector, and more accurate and wider range measurement is possible by “calibration without attenuation” and “vacuum gauge calibration”. I have to.
- FIG. 6 is a view showing an apparatus for measuring the mean free path according to the second embodiment of the present invention.
- a composite ion source and a transmission collector are used, and countermeasures against stray ions and an ion opening angle are shown. Measures against accuracy degradation due to the above are taken.
- the ion source 100, collector-202, and collector 203 are exactly the same as in the first embodiment, and the measurement procedure, calculation method, vacuum range, and the like are also the same.
- stray ion blocking plates 401a and 401b are newly installed as a countermeasure against mechanical stray ions.
- the beam angle limiting plate 400 has a hole (about 2 mm) at the center, and is installed near the ion source 100 (about 2 mm from the end).
- the stray ion blocking plates 401a and 401b have holes with meshes (mesh interval 1 mm, transmittance 90%) at the center.
- the stray ion blocking plate 401a is disposed at a distance of about 2 mm from the collector 202, and the hole ⁇ is about 3 mm.
- the stray ion blocking plate 401b is disposed at a distance of about 2 mm from the collector 203, and the hole ⁇ is about 9 mm.
- the stray ion absorbing plate 402 has a cylindrical shape (about ⁇ 10 mm) and is installed coaxially with the ion 110 beam.
- the beam angle limiting plate 400 and the stray ion absorbing plate 402 have a ground potential (0V), and both of the stray ion blocking plates 401a and 401b have a potential of + 95V, which is 5V lower than the voltage of the grid 102.
- the three holes of the beam angle limiting plate 400 and the stray ion blocking plates 401a and 401b are the opening angle at which the beam angle limiting plate 400 is viewed from the ion source 100, and the holes of the two stray ion blocking plates 401a and 401b from the ion source 100.
- Three of the expected opening angles are "same opening angle”.
- the opening angle of the holes of the stray ion blocking plates 401a and 401b is important, and as a result, the opening angle of the ions 110 reaching the two collectors 202 and 203 is the same as the opening angle seen from the ion source 100.
- the beam of ions 110 whose opening angle is limited by the beam angle limiting plate 400 passes through the holes of the stray ion blocking plates 401a and 401b and reaches the collectors 202 and 203 as long as they do not collide with the atmospheric gas.
- the ions 110 that have spread beyond a predetermined opening angle and the ions 110 that have lost the initial kinetic energy are cut, and only the ions 110 that do not collide with the atmospheric gas reach the collector.
- mechanical measures are taken against stray ions.
- the two collectors 202, 203 always (even if the degree of vacuum changes) Suffice to capture the same ion flux.
- the three holes are set to “the same opening angle” as in the above-described countermeasure against stray ions.
- the beam angle limiting plate 400 is not absolutely essential. However, the provision of the beam angle limiting plate 400 provides an initial countermeasure for stray ions in that useless ions cannot enter the ion flight region, and causes a deterioration in accuracy in that the ion extraction angle is more reliably fixed. Can be thoroughly implemented. In addition, since an electrode having a ground potential is installed near the ion source 100, it is possible to expect the ions 110 to be stably extracted from the ion source 100, that is, an effect as an extraction electrode. As described above, in the present embodiment, countermeasures for stray ions are strictly performed, and the measurement accuracy can be greatly improved.
- FIG. 7 is a diagram showing an apparatus for measuring the mean free path according to the third embodiment of the present invention.
- a complex ion source and a transmission collector are used, and the accuracy deterioration factor due to the ion opening angle is shown.
- Countermeasures against electric stray ions are being taken.
- the ion source 100, the collector 202, and the collector 203 are almost the same as those in the first embodiment, and the measurement procedure, calculation method, vacuum range, etc. are the same, but the size of the collector 202 and the collector 203 (effective detection surface). Is unique.
- ion blanking is newly installed as a measure against electrical stray ions, and a lock-in (modulation synchronization) amplifier is used as an ammeter.
- the detection effective surfaces of both the collector 202 and the collector 203 are always in the ion 110 beam, and the two detection effective surfaces are A bundle of the same ions 110 is always measured.
- This countermeasure is basically the same as the “same opening angle” in the second embodiment.
- the ions 110 having a certain opening angle or more are cut by the plates with holes (stray ion blocking plates 401a and 401b), whereas in this embodiment, the size of the collectors 202 and 203 (detection) Since the effective surface is matched with a certain opening angle, ions 110 having a larger opening angle are allowed to pass through without being measured. Since the collector 202 and the collector 203 are suspended by three thin wires (about ⁇ 0.1 mm), the influence of the ions 110 having an opening angle larger than that of the collector can be ignored.
- an ion blanking 501 is installed in the vicinity of the ion source 100 so that the ions 110 are intermittently emitted.
- a number of blanking methods for periodically interrupting charged particles are known.
- the simplest blocking potential method using a mesh is employed.
- any means may be used as long as incident charged particles can be emitted in an intermittent cycle.
- the mesh of the ion blanking 501 has a mesh interval of 1 mm and a transmittance of about 90%, and a power source 504 is electrically connected to the mesh and a rectangular voltage 505 is applied. That is, potentials of 0 V and 100 V are applied to the mesh at about 1 MHz (10 6 cycles / second). Since the ions 110 cannot pass through when the mesh is 100 V, the ions 110 are intermittently emitted at about 1 MHz. Therefore, ion currents that reach the collectors 202 and 203 in 1 ⁇ sec (10 ⁇ 6 sec) or less after flying at high speed without colliding with the atmospheric gas become rectangular waves of the same frequency.
- the ion current that has reached the collectors 202 and 203 after 10 ⁇ sec (10 ⁇ 5 sec) or more has become almost constant. That is, stray ions have a constant current, and the ion current to be used as a signal is a rectangular wave superimposed thereon. Since the voltage 505 (synchronization signal) obtained by dividing the blocking potential is input to the lock-in (modulation synchronization type) amplifier 502, the signal intensity of the AC component synchronized with the frequency is measured. That is, only the original signal that is alternating current is detected, and stray ions that are constant current are not detected. Note that the collector to be compared with the lock-in amplifier 502 can be selected by the switch 503.
- reference numeral 506 denotes an ion current detected at the collector when it does not collide with the atmospheric gas
- reference numeral 507 denotes an ion current detected at the collector when it collides with the atmospheric gas
- reference numeral 508 is an ion serving as a signal (an ion that has reached the collector without collision)
- reference numeral 509 is a stray ion serving as noise.
- countermeasures for accuracy degradation are taken by reducing the effective detection areas of the collectors 202 and 203, and stray ions are taken by using a lock-in (modulation-synchronous) amplifier 502.
- a lock-in (modulation-synchronous) amplifier 502. Have gained. Due to this synergistic effect, it is possible to improve accuracy and take measures against stray ions without providing three electrodes on the beam angle limiting plate, stray ion blocking plate, and stray ion absorbing plate, which were necessary in the second embodiment. .
- each of these countermeasures can be used independently because it exhibits usefulness alone.
- FIG. 9 is a view showing an apparatus for measuring the mean free path according to the fourth embodiment of the present invention, and the apparatus does not have an ion source for measurement, and comes from an atmosphere to be measured such as plasma. Ion is used.
- Each electrode is substantially the same as that of the second embodiment (FIG. 6), and the apparatus 1007 includes stray ion blocking plates 401a and 401b, stray ion absorbing plates 402, and a shield case 603.
- Shield case 603 has the same function as beam angle limiting plate 400 and surrounds the entire electrode portion to prevent stray ions from entering.
- the potential of the shield case 603 is ground (0 V).
- the shield case 603 is a metal plate (thickness of about 1 mm) made of SUS, etc., and a side surface facing the plasma 601 is provided with a hole (about ⁇ 2 mm), and other than the hole is sealed. It is.
- the potential of stray ion blocking plates 401a and 401b can be changed from + 5V to about + 50V.
- the dimensions, materials, and potentials of the other electrodes are all the same as in the second embodiment.
- the measurement procedure other than the ion source described below is the same as in the second embodiment, and the calculation method, the vacuum range, etc. are exactly the same.
- the apparatus 1007 further includes a plasma shield plate 602 and means (not shown) for generating plasma 601 in the plasma shield plate 602.
- the plasma 601 can be generated by a commonly used method.
- plasma depressurized plasma
- the vacuum vessel Normally, as a countermeasure against contamination of the inner wall of the vacuum vessel and the vacuum parts, it is generated in the area covered by the plasma shield plate 602. It is installed outside the shield plate 602 (between the inner wall of the vacuum vessel).
- the plasma shield plate 602 must have a high degree of sealing in order to adequately take measures against dirt, but in that case, the degree of vacuum differs between the inside and outside of the plasma shield plate 602, and the degree of vacuum inside the plasma shield plate 602 is essential.
- the conventional vacuum gauge requires an absolute value of a minute current, it is impossible to install it inside the plasma shield plate 602 where ions and electrons from the plasma 601 are present in a high concentration.
- this embodiment can realize this with a simple structure.
- the apparatus is not equipped with an ion source, but since positive ions having a high energy of about 10 to 30 eV are normally emitted from the center of the plasma, the ions from the plasma 601 are used for measurement. Use 120.
- the current amount of ions to be measured is not related to the measurement result, and only the current amount ratio between the first and second collectors is required. Therefore, in this embodiment, the amount of current cannot be known, and even if it fluctuates, measurement can be performed without any problem.
- ions from plasma with a larger amount of lower energy also exist, only positive ions with higher energy are measured by adjusting the potentials of stray ion blocking plates 401a and 401b to distinguish them.
- the electrodes in the shield case 603 are the same as those in the second embodiment (FIG. 6), but the configuration in the shield case 603 may be the same as in the third embodiment (FIG. 7). That is, a simple structure in which the ion blanking 501 and the collectors 202 and 203 are installed in the shield case 603 can be obtained. However, the low potential (potential at the bottom of the rectangular wave) applied to the mesh by ion blanking 501 is variable from + 5V to + 50V instead of 0V (high potential remains at about 100V), and ions 110 with low energy Eliminate. In addition, there is an advantage that the electrical influence from the plasma 601 (and the plasma generator) can be eliminated by using a lock-in amplifier.
- the plasma region can be measured by using ions from the plasma, which has been impossible in the past.
- FIG. 10 is a view showing an apparatus for measuring the mean free path according to the fifth embodiment of the present invention, and the apparatus 1007 according to this embodiment is suitable for an area having a lower degree of vacuum than the above embodiments. .
- the lower view is a front view
- the upper view is a top view.
- the transmission type collector 202 is the same as that in each of the above embodiments, but a simple one is used for the ion source 100, and the entire shape is elongated.
- the ion source 100 includes only a plate 102 made of SUS or the like (about 8 mm ⁇ 2 mm, impermeable to electron transmission) and a filament 101 made of W wire ( ⁇ 0.2 mm, length of about 8 mm).
- the grid is plate-like and ionized in the vicinity of the grid, so it is necessary to transmit the electrons. Rather, it is just a clogged plate rather than a mesh // lattice.
- a voltage is applied to the grid 102 at + 100V and the filament 101 at about + 30V, and the distance between them is about 1 mm.
- Electrons 310 emitted from the filament 101 travel toward the grid 102 and collide with the ambient gas in the vicinity of the grid 102 to generate positively charged ions 110. Since the ions 110 are generated almost at the potential of the grid 102 (+100 V), the ions 110 travel in the direction opposite to the beam of the electrons 310 toward the shield case 603. Since a slit (about 8 mm ⁇ 2 mm) is provided on the front surface (grid 102, filament 101 side) of the shield case 603, the ions 110 that have reached the slit proceed to the inside of the shield case 603. The distance between the grid 102 and the front surface of the shield case 603 is about 3 mm, and the distance between the front surface of the shield case 603 and the collector 202 is 1 mm.
- the collector 202 (about 5 mm ⁇ 1.5 mm) is a mesh made of SUS (interval of 0.3 mm, transmittance of about 50%), and the collector 203 (about 5 mm ⁇ 1.5 mm) is a plate made of SUS.
- the distance between the collector 202 and the collector 203 is exactly 5 mm.
- the shield case 603 is a metal plate (thickness of about 1 mm) made of SUS or the like and surrounds both the collectors 202 and 203 so that stray ions do not enter from outside (closed compared to the plasma of FIG. 9). The degree is not severe).
- the shape of the shield case 603 is elongated (and the ion 110 beam is also elongated) like a cigarette case. Accordingly, stray ions generated in the ion flight region are more likely to be absorbed by the shield case 603 that is present closer than the collector that is present in the distance.
- the shield case 603 is connected to an ammeter so that ion current flowing into the shield case 603 (mainly near the front slit) can be measured, and corresponds to the internal collector 201 in FIGS. Yes.
- the front surface of the shield case 603 has a structure that captures some ions and transmits other ions in the same manner as the permeated collector 202, so it functions as an internal collector by correcting without attenuation. Can be fulfilled. That is, the shield case 603 has functions of blocking and absorbing stray ions and functions of an internal collector. In terms of potential, both the collectors 202 and 203 and the shield case 603 are grounded (0 V).
- a vacuum gauge with plate-like grids and collectors arranged on both sides of the filament is known as a Schulz gauge. Although it is based on the same principle as an ion gauge with a cylindrical grid, the applied vacuum is about 0.1 Pa to 100 Pa, which is poor. We are shifting towards. That is, the principle that the electrons generated from the filament are accelerated by the grid and collided with the atmospheric gas to generate ions, and the ions are collected by the collector and the ion current is measured is exactly the same. However, by bringing the grid into a plate shape and making it close to the filament, the ion generation efficiency is reduced to reduce the effect of space charge by ions, and the collector is also brought closer to promote ion trapping, so that the ion gauge has reached its limit.
- the measurement procedure of the mean free path according to this embodiment is exactly the same as that of the first embodiment, and when high accuracy is required, “calibration without attenuation” is performed in advance.
- the distance between the collector 202 and the collector 203 is 5 mm, and the distance between the front surface of the shield case 603 as the internal collector and the collector 202 is as short as 1 mm. Therefore, measurement is performed at about 0.4 Pa to 6 Pa in the former equation (5) and about 2 Pa to 30 Pa in the latter equation (3).
- “vacuum gauge calibration” is the same as that of the first embodiment, but the operation is similar to the Schulz gauge, so that measurement of about 0.1 Pa to 100 Pa can be performed.
- FIG. 11A is a diagram showing an apparatus for measuring the mean free path according to the sixth embodiment of the present invention.
- 11A is a top view of the device 1007 according to this embodiment, and the lower view is a front view.
- FIG. 11B is a diagram showing a filament grid control circuit of the apparatus 1007 shown in FIG. 11A.
- the apparatus 1007 according to this embodiment can switch charged particles used for measurement between ions and electrons so that a wider range of measurements can be performed.
- the portion to be installed in the atmosphere is the same as that of the fifth embodiment except for the applied voltage, but the filament grid control circuit is new.
- the filament 101 is set to about ⁇ 30 V, and the same potential as that of the filament 101 is applied to the grid 102. That is, as shown in FIG. 11B, the switches 1101 and 1102 are switched to apply a potential of ⁇ 30 V to the filament 101 and the grid 102. By this switching, the traveling direction of the electrons is reversed, and electrons are introduced into the flight region on the opposite side of the grid 102 (right side in FIG. 11A). The electrons 310 emitted from the filament 101 are attracted to the shield case 603 having the ground potential, and proceed to the inside of the shield case 603 from the slit.
- the electron 310 operates in the same manner as in the case of ions such as the subsequent collision with the atmospheric gas and the arrival and measurement of the collectors 202 and 203, but the mean free path is five times longer than the ions, so the applied vacuum is It may be about 5 times worse.
- the collision energy to the collector is about 30 eV, so the influence of secondary electron emission in electron current measurement is small.
- the mean free path can be measured over a wide range of 0.4 Pa to 200 Pa by switching between ions and electrons.
- FIG. 12A is a diagram showing an apparatus for measuring the mean free path according to the seventh embodiment of the present invention.
- 12A is a top view of the device 1007 according to the present embodiment, and the lower view is a front view.
- FIG. 12B is a diagram showing a filament control circuit of the device 1007 shown in FIG. 12A.
- the apparatus 1007 according to the present embodiment has a simpler structure for exclusive use for electronics and has the function of a Pirani gauge using the same filament 101.
- the part installed in the atmosphere is the same as that of the sixth embodiment except that no grid is present, but the filament control circuit is new as shown in FIG. 12B.
- the operation / procedure for measuring the mean free path by the electron 310 is exactly the same as in the sixth embodiment, and “calibration without attenuation” and “vacuum gauge calibration” are performed as necessary.
- Pirani gauge is robust and highly versatile, and is widely used for many purposes.
- Pirani gauges have a wide range of applicable vacuum levels of about 1 Pa to 1000 Pa. However, as with ion gauges, the sensitivity (converted value) of the absolute value of the signal amount, which is a significant change, is a drawback. "Positive” is very effective. “Vacuum gauge calibration” is the same as in the first embodiment, and the Pirani gauge is compared with the measured value of the mean free path and the measured value by the Pirani gauge while maintaining the degree of vacuum at which attenuation is caused by the known gas species. Calibrate the sensitivity (converted value). This allows direct measurement of the mean free path of about 2 Pa to 150 Pa, as well as Pirani gauge measurement of about 1 Pa to 1000 Pa.
- vacuum gauge calibration enables highly accurate measurement with a versatile Pirani gauge.
- FIG. 13A is a diagram showing an apparatus for measuring a mean free path according to an eighth embodiment of the present invention.
- 13A is a top view of the device 1007 according to the present embodiment, and the lower view is a front view.
- 13B is a diagram showing the shape of each electrode of the apparatus shown in FIG. 13A
- FIG. 13C is a diagram showing an electron beam trajectory along line A in FIG. 13B
- FIG. 13D is a diagram showing line B in FIG. 13B.
- the shape of the collector is devised so as to cope with the use of an electron source having a wide width (area) and the absence of “calibration without attenuation”.
- the filament system which is as high as 1800 ° C, has problems such as reaction with the ambient gas, and an indirectly heated oxide cathode and other low-temperature electron sources that can lower the temperature are desired.
- an electron source has a significantly low luminance (electron intensity, electron emission amount per unit area and unit angle). Further, depending on the application, it is impossible to sufficiently improve the degree of vacuum of the atmosphere, and “calibration without attenuation” may not be used.
- the electron source 300 is an indirectly heated oxide cathode, which is about three times longer (about 25 mm) and wider (about 3 mm) than the filament.
- the beam angle limiting plate 400 is provided with four holes (small windows) of about 1.5 mm ⁇ 3 mm at equal intervals.
- the collector 202 is provided with two holes (small windows) of about 2 mm ⁇ 4 mm so as to partially overlap the holes of the beam angle limiting plate 400.
- the collector 203 does not have a hole (small window).
- the intervals of the surface of the electron source 300, the beam angle limiting plate 400, the collector 202, and the collector 203 are about 5 mm, 1 mm, and 5 mm, respectively, and their outer shapes are about 30 mm ⁇ 8 mm.
- a stray electron absorbing plate 412 is installed between the collector 202 and the collector 203.
- the beam angle limiting plate 400, the collector 202, the collector 203, and the stray electron absorbing plate 412 are all plates (plates) made of SUS having a thickness of about 0.5 mm.
- the potential of the electron source 300 is ⁇ 30V, and the stray electron absorbing plate 412 is + 5V, but the others are all ground potential (0V).
- the electrons 310 emitted from the electron source 300 travel toward the beam angle limiting plate 400 and pass through four holes (small windows) of the beam angle limiting plate 400.
- the electrons that have passed through the two holes are detected by the collector 202.
- electrons passing through the remaining two holes also pass through the holes (small windows) of the collector 202 and are detected by the collector 203.
- the former situation is shown in FIG. 13C and the latter situation is shown in FIG. 13D.
- the reason why the size of the hole (small window) is made larger in the collector 202 than in the beam angle limiting plate 400 is to prevent the collector 310 from detecting the electrons 310 flying to the collector 203.
- the reason why the two holes (small windows) of the collector 202 are not symmetrical with each other is to cancel the influence of the amount of electrons 310 emitted from the electron source 300 being not uniform in the longitudinal direction. As a result, the detection rates of the electrons 310 of the collector 202 and the collector 203 are both 50%.
- the beam angle limiting plate 400 having a larger number of holes (openings) than the number of holes (openings) provided in the transmission type collector 202 is provided between the electron source 300 and the collector 202. ing. Further, a part of the electrons (for example, 50%) passing through the hole provided in the beam angle limiting plate 400 is captured by the collector 202, and the other electrons (for example, 50%) are allowed to pass through.
- the hole provided in the angle limiting plate 400 and the hole provided in the collector 202 are positioned.
- the operation / procedure for measuring the mean free path by the electron 310 and the vacuum range are the same as those in the seventh embodiment.
- the collector 202 has a large area of one hole (small window) unlike the mesh shape in the previous embodiments, the transmittance can be accurately estimated, and the transmittance can change due to dirt, etc. Because there is almost no need for calibration without attenuation. That is, the mesh is most easily used to realize the transparency of the collector 202, but there is a difficulty in determining an important transmittance, which is covered by calibration without attenuation.
- the opening formed in the collector 202 is formed by punching a plate, and the area of one opening is increased to reduce the influence of deformation and dirt.
- the transmittance can be determined by calculation. As a result, measurement can be performed with a certain degree of accuracy without calibration without attenuation.
- a stray electron absorbing plate 412 to which a potential is applied is necessary. That is, the distance between the collector 202 or the collector 203 and the stray electron absorbing plate 412 is not so different for stray electrons, so if this space has a constant potential, a considerable amount of stray electrons can flow into both the collectors 202 and 203. There is sex. Therefore, a potential of plus 5 V is applied to the stray electron absorbing plate 412 so as to actively draw electrons.
- the stray electrons are absorbed by the stray electron absorbing plate 412 without reaching both the collectors 202 and 203. Since electrons that should reach the collector 203 without colliding with the atmospheric gas have kinetic energy of 30 V, they are normally measured by the collector 203 normally without being affected by the stray electron absorbing plate 412. . However, since the electron source is wide, it is somewhat impossible to prepare an electrode corresponding to the internal collector as in the fifth to seventh embodiments, so it is not included in this embodiment.
- a low temperature indirectly heated electron source can be used, and highly accurate measurement can be performed without performing “calibration without attenuation”.
- FIG. 14A is a diagram showing an apparatus for measuring the mean free path according to the ninth embodiment of the present invention.
- 14A is a top view of the device 1007 according to the present embodiment, and the lower view is a front view.
- FIG. 14B is a diagram showing the shape of each electrode shown in FIG. 14A and their circuits.
- the range of the applicable vacuum degree is expanded by using many collectors in addition to the wide electron source and the realization without “calibration without attenuation”.
- the basic structure and operation are the same as those in FIG. 13 of the eighth embodiment, but a lock-in (modulation synchronization type) amplifier 502 is used as the number of collectors increases. Therefore, in this embodiment, it is not necessary to use a stray electron absorbing plate.
- the electron source 300 is exactly the same as the electron source of the eighth embodiment.
- the beam angle limiting plate 400 is provided with 10 holes (small windows) of about 1 mm ⁇ 2.5 mm at equal intervals.
- the collector 202 is provided with eight holes (small windows) of about 1.5 mm ⁇ 3 mm so as to overlap with the holes of the beam angle limiting plate 400.
- the collector 203 is provided with six holes (small windows) of about 2 mm ⁇ 3.5 mm so as to overlap the holes of the collector 202.
- the collector 204 is provided with four holes (small windows) of about 2.5 mm ⁇ 4 mm so as to overlap the holes of the collector 203.
- the collector 205 is provided with two holes (small windows) of about 3 mm ⁇ 4.5 mm so as to overlap the holes of the collector 204.
- the collector 206 has no holes (small windows).
- the distance between the surface of the electron source 300 and the beam angle limiting plate 400 is about 5 mm, and the distance from the collector 202 to the collectors 203, 204, 205, 206 is 0.15 mm, 0.5 mm, 1.5 mm, 5 mm. Yes. These external shapes are approximately 30 mm ⁇ 8 mm.
- the beam angle limiting plate 400 and the collectors 202 to 206 are all plates made of SUS or the like having a thickness of about 0.5 mm. Except for the electron source 300 (the potential of the electron source 300 is ⁇ 30V), the potentials of all the electrodes are the ground potential (0V).
- the five collectors 202 to 206 detect only the electrons 310 that have passed through two holes (small windows), respectively, among the electrons 310 that have passed through the ten holes (small windows) of the beam angle limiting plate 400. Therefore, the detection rate of the electrons 310 of each collector is 20%. Note that the number of electrons (number of charged particles) detected by the collectors 204 to 206 is stored in the RAM 1003 in the same manner as the collectors 202 and 203.
- a lock-in (modulation synchronization type) amplifier 502 that electrically eliminates stray electrons is used.
- the configuration and operation of the lock-in (modulation synchronization type) amplifier are basically the same as those of the third embodiment (FIGS. 7 and 8).
- electrons are used instead of ions, but the polarities are different and the collector arrival time in non-collision is only shortened.
- a rectangular wave potential of ⁇ 30 V is applied to the electron source 300 instead of the blocking mesh, but the beam is similarly blanked.
- collector switching is increasing.
- the collectors are switched by the switches 1402 and 1403. That is, the switch 1402 functions as a switch for selecting a collector to be compared, and the switch 1403 functions as a switch for selecting a vacuum range (electronic flight distance).
- the flight distance of electrons increases from the collector 202 toward the collector 206.
- the flight distance of electrons between the collectors increases as the distance from the collector 202 to the collector 206 increases. Therefore, the vacuum degree range that can be measured varies depending on which collector is set as the first collector and the second collector.
- the vacuum degree range by each collector is about 60 Pa to 900 Pa.
- the vacuum range is about 20 Pa to 300 Pa.
- the degree of vacuum is about 6 Pa to 90 Pa.
- the degree of vacuum is about 2 Pa to 30 Pa. (Both are calculated according to equation (5)) Therefore, the applicable vacuum range as a whole is as wide as 2 Pa to 900 Pa.
- the mean free path can be measured over a wide range of 2 Pa to 900 Pa by switching the collector.
- FIG. 15A is a view showing an apparatus for measuring the mean free path according to the tenth embodiment of the present invention
- FIG. 15B is a cross-sectional view taken along line AA ′ of FIG. 15A.
- different flight distances can be measured with one collector without changing the mechanical structure.
- the principle of changing the distance is based on the fact that electrons move in a spiral motion when a magnetic field parallel to the traveling direction (axial direction) exists, and the number of spirals depends on the velocity (kinetic energy) in the traveling direction.
- the charged particles to be used can be ions, but electrons are used in this embodiment because there is a problem that a strong magnetic field is required and the helical motion (diameter) changes depending on the gas species.
- the filament 101, the filament case 320 surrounding the filament 101, and the orbital potential adjusting plate 703 are installed between the two magnets, and the shield case 603 surrounds the whole.
- the magnets are conductive magnets (such as alnico), each having a diameter of about 60 mm ⁇ 5 mm.
- One magnet serves as a repeller that repels electrons 310, and the other magnet serves as a collector.
- the former is a repeller magnet 701, and the latter is a collector magnet 702. The distance between them is about 80 mm, and the magnetic field between them is adjusted to 16 gauss.
- the filament 101 is a W-made wire with a diameter of about 0.2 mm and is a hairpin type (the tip is bent at an acute angle).
- the filament case 320 is a box having a thickness of about 0.3 mm and a size of about 6 mm ⁇ 3 mm ⁇ 30 mm, and has a circular hole with a diameter of about 1 mm on the upper surface, and is positioned so that the tip of the filament 101 matches the center of the circular hole. This is well known as a method of forming a thin electron 310 beam.
- the circular hole of the filament case 320 is located about 2 mm away from the repeller magnet 701 in the axial direction and about 20 mm away from the shaft, and faces the circumferential direction.
- the orbital potential adjusting plate 703 is a double cylinder (the inner diameter of the outer cylinder is about ⁇ 45 mm, the outer diameter of the inner cylinder is about ⁇ 35 mm, and electrons pass between ⁇ 35 mm and ⁇ 45 mm).
- the speed of 310 in the axial direction changes, and the number of spirals of the electron spiral motion can be adjusted.
- the distance (axial direction) between the orbital potential adjusting plate 703 and the magnet 702 is about 5 mm.
- the filament case 320 and the orbital potential adjusting plate 703 are made of SUS because they need to be electrically conductive and non-magnetic.
- the shield case 603 is made of pure iron (or magnetic stainless steel) having a thickness of about 5 mm, and serves not only to shield against disturbance magnetic fields but also to serve as a magnet yoke.
- the potential of each electrode is set as follows.
- the potential of the repeller magnet 701 is set to -30 V
- the potential of the collector magnet 702 is set to 0 V
- the potential of the filament 101 is set to -130 V
- the potential of the filament case 320 is set to -30 V
- the potential of the orbital potential adjusting plate 703 is set to 0 V.
- the electron 310 is emitted with a kinetic energy of 100 V in the circumferential direction (difference between the potential of the filament 101 of ⁇ 130 V and the potential of the filament case 320 of ⁇ 30 V), but a magnetic field of 16 Gauss is generated in the axial direction (left and right in the figure).
- the electron 310 When traveling in the axial direction with a kinetic energy of 30 eV, the electron 310 performs a helical motion of approximately one revolution before reaching the collector-cum-use magnet 702. Next, if other conditions remain the same and only the orbital potential adjusting plate 703 is changed to a potential of ⁇ 29 V (ie, 1 eV kinetic energy), a helical motion of 5.5 rotations is performed. Thus, by changing the potential of the orbital potential adjusting plate 703, the substantial flight distance can be changed even with the same collector.
- the mean free path can be calculated in the same manner as in the embodiment in which two collectors exist so far.
- symbols 310a and 310b schematically represent this state. That is, when a potential of 0 V is applied to the orbital electron adjusting plate 703, the electrons emitted from the filament case 320 follow the trajectory of reference numeral 310a, perform a spiral motion for one rotation, and are detected by the collector and magnet 702.
- the stray electrons that have lost the kinetic energy by colliding with the atmospheric gas have a small helix diameter and are less likely to pass between the inner and outer diameters of the orbital potential adjusting plate 703, so the stray electrons are less affected.
- the collision energy of the electron 310 to the collector is about 130 eV (approximately equivalent to the difference between the potential of the filament 101 of ⁇ 130 V and the potential of the collector 702 of 0 V)
- the secondary electron emission rate is high, but the kinetic energy is small. Since the secondary electrons have a small helical diameter, they are returned to the collector by the potential gradient without being scattered. Therefore, the influence of secondary electron emission is small.
- the potential of the filament 101 (the kinetic energy in the circumferential direction of the electrons 310) is adjusted so that the electron current received by the collector electrode 702 is maximized before the measurement. This is because, at the maximum current, the helical diameter of the electron 310 should be between the outer cylinder inner diameter and the inner cylinder outer diameter of the orbital potential adjusting plate 703, so that the flight distance can be estimated correctly.
- the actual flight distance is the square root of the sum of the square (square) of “distance between collectors” and the square (square) of “spiral diameter ⁇ number of spirals ⁇ ⁇ ”.
- the distance between the collectors is 80 mm
- the spiral diameter is 40 mm. Therefore, the flight distance is 149 mm for one spiral and 820 mm for 5.5 revolutions. Therefore, the flight distance 149mm in helix 1 rotation L1, the electron current and I L1, whereas, the flight distance 533mm in 5.5 rotation L2, the mean free path is calculated from equation (5) the electron current as I L2.
- the applicable vacuum range is about 0.02 Pa to 0.3 Pa at 1 & 5.5 revolutions.
- the potential applied to the orbital potential adjusting plate 703 and the flight distance corresponding to the potential are stored in association with each other in a table. Since the number of spirals is determined by the potential applied to the orbital potential adjusting plate 703, the control unit 1000 detects the first detected by the collector-cum-use magnet 702 when the first potential is applied to the orbital potential adjusting plate 703. The number of electrons (electron current) and the second number of electrons (electron current) detected by the collector and magnet 702 when the second potential is applied to the orbital potential adjusting plate 703 are stored in the RAM 1003, respectively.
- the control unit 1000 refers to the table, and the first flight distance corresponding to the first potential to the orbital potential adjustment plate 703 and the second potential corresponding to the second potential to the orbital potential adjustment plate 703.
- the flight distance (second flight distance> first flight distance; therefore, the first flight distance is L1 and the second flight distance is L2) is acquired, and the first electron number I L1 and the RAM 1003 are obtained.
- a second number of electrons IL2 is acquired.
- the control unit 1000 calculates the mean free path using Equation (5), as in the first embodiment.
- the number of electrons detected by an ammeter connected to the collector-cum-use magnet 702 may be displayed.
- the user inputs the value displayed on the ammeter and the flight distance corresponding to the value to the control unit 1000 via the input operation unit 1005, and further inputs an instruction for calculating the mean free path.
- the control unit 1000 obtains the flight distance and the number of electrons by these user inputs, and calculates the mean free path by any one of the equations (3) to (5) in accordance with the above calculation instructions.
- the user may input the value displayed on the ammeter into the scientific calculator. In this case, according to the user input, the scientific calculator obtains the flight distance of the electrons and the number of attenuated electrons, and the scientific calculator can perform any of the equations (3) to (5). .
- the arithmetic device for calculating the mean free path (the control unit 1000, a computer separate from the control unit 1000, a scientific calculator, etc.) is transmitted from the device 1007 or input such as a keyboard or a touch panel. According to a user input via the operation unit, the flight distance of electrons and the number of electrons after attenuation can be acquired.
- the ion source is not limited to the above-described embodiment, and any ion / current type, magnetic field (magnetron) type, alkali metal type, liquid metal type, etc. can be used as long as ions with a current of about mA to nA are emitted.
- Alkaline metal type that heats sintered alumina silicate containing Li oxide and releases Li + ions, etc. or liquid that discharges Au + ions and so on by applying high voltage to Au heated to liquid form
- the metal type is not an atmospheric gas ion, but is applicable because specific ions such as Li and Au are supplied. Further, negative ions may be used.
- the electron source can be arbitrarily selected from a discharge / plasma type, a field emission type, a photoelectron emission type, and the like as long as electrons having a current comparable to that in the above-described embodiment are emitted.
- the detector is not limited to the plate-shaped or mesh-shaped collector in the above embodiment, but may be a Faraday cup-shaped collector, a multi-channel plate or an electron multiplier.
- one ion source and a plurality of collectors are used, but conversely, one collector and a plurality of ion sources can be used, or a set of one ion source and one collector (the same configuration as the conventional one). ) Can be prepared.
- both the first charged particle number and the second charged particle number can be measured simultaneously, or both can be measured by switching in a short time. I can do it.
- each current is not measured by each detection circuit, but a detection circuit capable of measuring the current ratio from the beginning is used. You can also
- the method for assembling the electrodes such as the collector is not limited to the charged particle generation configuration in which the conventional vacuum gauge (ion gauge or Schulz gauge) in the above embodiment is manufactured by a similar mechanical method, and has been developed from semiconductor technology.
- Microfabrication technology can also be used. According to MEMS, it is easy to shorten the flight distance, so it is suitable for measurement at a worse vacuum.
- the “vacuum gauge calibration” for calibrating the conventional vacuum gauge is not limited to the one incorporated in the apparatus of the present invention as in the above embodiment, and exchanges signals with other independent gauges by cable connection or the like. You can also do it. That is, for example, the device 1007 can transmit the calculated mean free path value itself or the pressure value obtained by converting from the mean free path value to the other independent vacuum gauge. . According to this, measurement accuracy can be increased while using the existing vacuum gauge.
- the calculation of the mean free path is not limited to the calculation formula in the above-described embodiment, but an expression obtained by adding an empirical correction term (empirical formula) based on this calculation formula can also be used. .
- the calculation formula of the mean free path in these programs is not limited to the above formula (3), formula (4), or formula (5), and formulas obtained by partially correcting these formulas can be used.
- Item 15 As described above in “Factors of deterioration in accuracy”, “deviation” from an ideal state always occurs, but the related conditions (ion current, ion energy, ion species, etc.) are the same. In many cases, the “deviation” is almost the same. Therefore, it is possible to obtain a calculation formula that experimentally (empirically) measures this “deviation” and corrects it, that is, a calculation formula including an empirical formula (correction term).
- a program using a calculation formula (L2 ⁇ L1) / In (I L1 / I L2 ) ⁇ F + G) including this empirical formula (for example, empirical formula F for multiplication and empirical formula G for addition) is used. By doing so, measurement with higher accuracy can be performed. Further, since the correction term depends on the related condition, a function of the correction term (for example, empirical formulas F and G) with the related condition as a variable is obtained by conducting an experiment under some conditions. Is possible. If this is used, more accurate measurement can be performed.
- the mass spectrometer required for measuring the degree of vacuum of each component is not limited to the quadrupole type, but a magnetic sector type, time-of-flight type, electric field / magnetic field superposition type that can arbitrarily set the distance between the ion source / collector. Etc. can also be used.
- the distance between the ion source and the collector is the same, the time from generation at the ion source to detection at the collector, that is, an ion trap type (three-dimensional type) in which an effective flight distance can be arbitrarily set. And a two-dimensional type) or an ion cyclotron type can also be used.
- the present invention can be applied to a system constituted by a plurality of devices (for example, a computer, an interface device, a reader, a printer, an apparatus 1007, etc.), or can be applied to an apparatus constituted by a single device.
- a plurality of devices for example, a computer, an interface device, a reader, a printer, an apparatus 1007, etc.
- an apparatus constituted by a single device for example, a computer, an interface device, a reader, a printer, an apparatus 1007, etc.
- Processing for storing a program for operating the configuration of the above-described embodiment so as to realize the function of the control unit 1000 of the above-described embodiment in a storage medium, reading the program stored in the storage medium as a code, and executing the program on a computer The method is also included in the category of the above-described embodiment. That is, a computer-readable storage medium is also included in the scope of the embodiments. In addition to the storage medium storing the computer program, the computer program itself is included in the above-described embodiment.
- a storage medium for example, a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, and a ROM can be used.
- processing is not limited to the single program stored in the above-described storage medium, but operates on the OS in cooperation with other software and expansion board functions to execute the operations of the above-described embodiments. This is also included in the category of the embodiment described above.
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Abstract
Description
従って、基板に垂直にイオンを入射させる為には、加速される領域で他の粒子と衝突させずに基板まで到達させることが肝要である。
ここで、イオンが加速される領域は、陰極の近傍に存在するカソードフォール又はシースと呼ばれている領域である。放電中で生じている電位の変化の多くはこの部分で生じている。この厚さは、放電空間の圧力及び基板ホルダへの印加パワー等に依存するが、典型的には10~30mm程度である。
従って、このカソードフォール又はシースの領域を衝突せずにイオンを通過させることが出来れば、基板に小さな拡がり角のイオンビームを入射させることが可能となる。
もし、実際のプロセスガス中での平均自由行程が分れば、プロセス条件を調整することにより、カソードフォール又はシース長より平均自由行程を長くすることにより、拡がり角の小さな入射イオンを得ることが出来る。
従来では、所定のガス雰囲気中で、所定のイオンの平均自由行程を求める場合、温度、ならびに所定のガスの粒子径および所定のイオンの径を求め、該値を用いてガス数密度や圧力から変換して平均自由行程を求めている(非特許文献1、2参照)。すなわち、従来では、平均自由行程を直接求めてはおらず、温度やガスの粒子径およびイオン径から間接的に計算により求めている。従って、イオンが移動する系の温度、および該イオンの径、雰囲気ガスの粒子径が分からなければ、平均自由行程を求めることはできなかった。
ここで、「ガス数密度」とは、ガスが分子の場合は単位体積当たりの分子の数、ガスが単原子分子の場合は単位体積当たりの原子数のことである。
このように、イオンのイオン径、雰囲気ガスの粒子径や温度が知られていない場合には、平均自由行程を圧力やガス数密度から変換することは困難となり、またこれらが知られても混合ガスの場合には変換計算が煩雑となる。
例えば、平均自由行程は、真空度を示すことができる。真空度(真空のレベル)を示す方法は、「ガス数密度」、「圧力」および「平均自由行程」の三つがあり、従来では、ガス数密度、または圧力が用いられている。この三つは雰囲気ガスの分子径や温度をパラメータとして互いに変換することが可能なので原理的には同じ量を示してはいるが、利用する現象としては全く別と言ってよいほど異なっている。
このように様々な分野で威力を発揮する平均自由行程を、煩雑な計算や測定を行うことなく、簡便かつ正確な方法で直接求めることは非常に有用であるが、現在は、平均自由行程を直接求める方法は確立されていない。
この減衰は、放射線元素の減衰と同じ指数関数的な現象であって、常にある時間(飛行距離)が進むと存在量が以前のある比率になるものである。習慣的に、放射線元素では存在量が半分になるまでの時間を半減期としているが、平均自由行程では1/e(0.37倍)となる飛行距離を平均自由行程としている。このように指数関数の減衰であるため、二つの異なる飛行距離での減衰量が分かると、数学的に減衰の強さ(すなわち、平均自由行程)を算出することが可能となるのである。
なお、「イオンに対応する中性分子」とは、該イオンがイオン化する前の中性分子である。
また、例えば、真空度を測定する分野にも適用することができる。
上述のように、真空度は、「ガス数密度」、「圧力」および「平均自由行程」の3つの量によって示すことができる。従来では、イオンゲージ(電離真空計)等によるガス数密度の計測、または隔膜真空計等による圧力(単位面積の壁を押す力)の計測により真空度を求めている。
ここで、イオン量とガス数密度との換算値のことは、一般には感度と言われる。
このように両者は、測定原理が異なるので適用できる真空度の領域が異なるものの、いずれも真空度(ガス数密度/圧力)に依存する量(イオン量/変形量)から換算値または換算式によって真空度を算出している点は同じである。
なお、以降説明では、荷電粒子としてイオンを用いる場合について説明するが、荷電粒子は電子であっても良いことは言うまでも無い。
まず、計算を簡単にするため、イオン源で発生するイオン数は真空度によらず一定として考える。
減衰前のイオン数をI0、飛行距離:L1の減衰後のイオン数をIL1、飛行距離:L2の減衰後のイオン数をIL2、平均自由行程をλとする。これらが図1Aに模式的に示されている。
IL1=I0・exp(-L1/λ) (1)
IL2=I0・exp(-L2/λ) (2)
式(1)または式(2)より、
λ=-L1/In(IL1/I0) (3)
λ=-L2/In(IL2/I0) (4)
が得られる。なお、“In”は自然対数である。式(3)、(4)からは、1つのコレクタにおける減衰後のイオン数から平均自由行程λを求めることができる。
また、式(1)および(2)より、
λ=(L2-L1)/In(IL1/IL2) (5)
が得られる。式(5)からは、2つのコレクタにおける減衰後のイオン数の比較から平均自由行程を求めることができる。なお、式(5)はI0と無関係となるので、高精度な測定が期待される。すなわち、式(5)を用いると、イオン源に望ましくない変動(I0が不意に変動しても)があっても、平均自由行程を求めるパラメータに含まれないので、上記変動があっても正確な平均自由行程を求めることができる。
図1Aにおける、飛行によりイオン数が減衰する状況が図1Bのグラフに示されている。横軸は雰囲気の真空度であり、縦軸は飛行後のイオン数を示す。なお、横軸は右に行くほど真空度が悪くなる、つまりガス数密度は大きくなるように示しているが、平均自由行程はガス数密度に反比例するので、横軸は右に行くほど平均自由行程は短くなる(すなわち、平均自由行程の逆数とみなせる)。図1Bにおいて、符号13は、飛行距離が短い場合であるイオン数IL1と真空度(平均自由行程)との関係を示すグラフであり、符号14は、飛行距離が長い場合であるイオン数IL2と真空度(平均自由行程)との関係を示すグラフである。
上記式(1)~(5)は、イオン源にて発生するイオン数は真空度に依存しないものとしていたが、イオンゲージや最も一般的なイオンゲージをベースとしたイオン源では真空度に依存してイオン数が変化する。すなわち、具体的に説明すると、図2Bの左側の部分のように、イオン電流の変化は図1Bの曲線に真空度の比例分が掛け合わされた形となる。図2Aが、イオン電流が真空度に依存するイオン源の場合の、本発明の平均自由行程を求める原理を説明するための模式図であり、図2Bが、図2Aにおける、飛行によりイオン数が減衰する状況を説明するための図である。
図2Aに示した、真空度依存のあるイオン源21a、21bが一般的なので、これについて説明する。イオン源21aは円筒型でかつ格子状など電子が透過できる形態のグリッド22aと加熱されて熱電子を放出するフィラメント23aとを備えている。グリッド22aは+100V、フィラメント23aは+30V程度に電圧が印加される。フィラメント23aより放出された電子はグリッド22aに向かって進むがほとんどの電子はグリッド22a内部にまで侵入し、そこで雰囲気ガスと衝突して正電荷のイオンを発生する。イオンはほぼグリッド22aの電位(+100V)で発生するのでアース電位のコレクタ24aに向かって進むことになり、コレクタ24aに流れる電流が発生したイオン数(イオン電流)となる。なお、イオン源21bも同様である。
真空度依存のあるイオン源を使って平均自由行程を求める方法を示す。ただし、簡単のため以下の3点が満足していることを前提とする。
α:測定に利用するイオン源が同じ真空度の、かつ同じ温度の領域に位置している。
β:測定に利用するイオン源が同じ数のイオンを発生する。
γ:各コレクタ(検出器)のイオンの検出効率は等しい。
λ = -60/ln(0.4/1.1)=60
となり、平均自由行程が60mmであると算出される(この場合は、平均自由行程と飛行距離がちょうど同じなので、イオン電流は1/e:0.37倍に減衰している)。
λ = -60/ln(0.33/2.4)=30
となり、平均自由行程が30mmであると算出される。
λ = -8/ln(3.3/12)=6
となり、平均自由行程が6mmであると算出される。
λ =-8/ln(1.8/25)=3
となり、平均自由行程が3mmであると算出される。
以上の計算はすべて飛行距離ゼロを減衰前の値としたが、コレクタ24aとコレクタ24bとの間での飛行による減衰に注目し、コレクタ24aでの値を減衰前、コレクタ24bの値を減衰後とすることも出来る。この場合にはイオン源からの引出し効率などの影響が入らないのでより高精度となる。これが式(5)に対応する。
λ =(60-8)/ ln(0.33/1.8)=30
となり、平均自由行程が30mmであると算出される。
なお、図4の点線44は飛行距離52mmでの減衰曲線であるが、これと式(3)を使っても同じ値が出る(数学的に等価)。
真空度を示す平均自由行程、ガス数密度、圧力の3つは以下の式によって変換することが出来る。
ガス数密度:n=K1・1/(d2・λ) (6)
圧力:P=K2・n・T=K3・T/(d2・λ) (7)
ただし、λは平均自由行程(m)、dは主成分の分子直径(m)、Tは温度(絶対温度:K)であり、P(圧力)の単位はPa(1N/m2)である。定数はK1=1/(√2・π)=0.225、K2=1.38×10-23J/K(ボルツマン定数)、K3=K1・K2となる。
飛行距離ゼロのイオンを測定するイオン源(B-Aゲージ)と外部コレクタにて検出させるためのイオンの出力とを、一つのイオン源で兼用することが出来れば、上記前提の「α:測定に利用するイオン源が同じ真空度・温度領域に位置する要件」を確実に満足するだけでなく、「β:測定に利用するイオン源が同じ数のイオンを発生する要件」をほぼ満足する。経済性や操作性・サイズ的なメリットも大きい。
そして、内部コレクタで計測されるイオンとほぼ同量のイオンがビームとして外部に放出されているので、内部コレクタによって減衰前のイオン電流I0が計測できることになる。しかし、厳密には同量ではないので、後述する「減衰なし較正」によってこの差を補正することが望ましい。
なお、第1~第3の実施形態(図5~7)では、複合型のイオン源を採用している。
本測定方法では必ず二つ以上のコレクタ(検出器)が必要となるが、それぞれにイオン源(イオンビーム)を用意するのは実用的ではない。この解決には、一つのイオン源(イオンビーム)に二つのコレクタを直列に設置(同一のイオンの飛行軸上に二つのコレクタを配置)して、イオン源に近い第1のコレクタでは一部のイオンは検出するが、残りのイオンはそのまま透過して、第1のコレクタよりも遠くに位置する第2のコレクタに進むようにすればよい。たとえば第1のコレクタをメッシュ状、スリット状あるいは少なくとも1つの小窓を設けた構造とする。あるいは、第1のコレクタは、導電性の部材を薄膜化したもの(例えば、シリコン薄膜)であっても良い。所定条件においては、導電性薄膜に荷電粒子が入射すると、その一部は該導電性薄膜に捕捉され、他の一部はそのまま透過する。このように、本発明では、透過型の第1のコレクタとしては、入射された荷電粒子の一部を検出し、他の一部を透過させることができる部材であればいずれの部材を用いても良い。そして平均自由行程の算出には第1のコレクタによるイオンの検出率によって本来の電流を較正する。
第1~第8の実施形態(図5~7、9~11、13~15)では、透過型の第1のコレクタを採用している。
より高い精度を実現するには上記項目9)の透過型の第1のコレクタでの物理的なイオン検出の比率だけでなく、電気的な検出比率(二つの計測回路の増幅率の差)を較正する必要がある。さらにI0(内部コレクタの値)を使用する場合には内外コレクタの比率較正も必須である。特に、汚れが顕著となる環境では、透過型の第1のコレクタの開口部(例えば、メッシュ)の透過率が変化することも懸念される。
読み取り誤差の観点からは、測定したい真空度範囲において二つの飛行距離でのイオン電流の比が概ね1.2倍以上、100倍以内となること、つまり、二つの飛行距離の差が平均自由行程の0.2倍から4倍程度とすることが望ましい(この0.2倍、4倍程度の値は、ln(IL1/IL2)=(L2-L1)/λより、ln1.2=0.18<0.2、およびln100=4.6>4 から算出される)。例えば、飛行距離が第1、第2のコレクタによる第1の飛行距離8mmと第2の飛行距離60mmとでは二つの飛行距離の差は52mmとなる。そこで、この52mm(飛行距離の差)が平均自由行程の0.2倍から4倍程度とするのが望ましいことから、この52mmの5倍(0.2倍の逆数)から0.25倍(4倍の逆数)までの平均自由行程、すなわち260mmから13mmまでの平均自由行程の真空度が適用できる範囲となる。圧力表示では、これは0.03Paから0.5Paとなる。
上記項目11)の真空度範囲で示された範囲は平均自由行程を直接計測する場合であるが、複合型のイオン源でのイオンゲージ機能と併用すれば、さらに真空度の範囲を広くすることが出来る。すなわち、通常のイオンゲージの測定範囲、すなわち1Pa~10-8Pa程度までの広い範囲において極めて正確な真空度の測定が可能となる。上記項目8)で示したように複合型のイオン源は感度(換算値)が半分であることを除けば従来真空計であるイオンゲージ(B-Aゲージ)と同じ機能・性能を持っている。しかし、もともとイオンゲージ(B-Aゲージ)は数桁以上の広大な範囲に渡ってリニアリティ(線形性)を保有するという優れた性能を持つ一方、感度(換算値)、すなわち信号量の絶対値は変化しやすいという欠点を持つ。図4での「減衰前(イオン源)のイオン電流」を示すグラフ41の右45度のラインがイオンゲージの真空度表示に対応するが、リニアリティ(線形性)が良好とはラインが直線となっていること、感度(換算値)が変化しやすいとはライン全体の上下位置がずれやすいことを意味している(図4は両対数グラフなので上下位置がずれるが、通常グラフにおいてはリニアティが変化するとは、傾きが変化することを言う)。
減衰をおこさせる荷電粒子としてはイオンだけでなく電子も利用することが出来る。電子は直径が小さいので平均自由行程はイオンのおよそ5.6倍になるので、同じ飛行距離であればイオンよりも5倍ほど良い真空度の測定に適用できる。電子の発生方法として最も一般的なものは熱フィラメント方式であるが、その他の電子源として傍熱型酸化物やフィールドエミッション型など、電子を発生できる方法であればいずれも使用することが出来る。第6~第10の実施形態(図11、13~16)では、電子を利用している。
雰囲気ガス(中性分子)と衝突したイオンや電子は消滅する訳ではなく、単に運動エネルギーを失うだけなので飛行空間に迷イオンや迷電子として残存・浮遊することになる。
そこで、これら迷イオン、迷電子といった迷荷電粒子を速やかに除去しないと、コレクタに到達してしまって荷電粒子量測定の誤差となり得る。この対策の一つは機械的なもので、計測に無関係な荷電粒子を飛行領域に入れないこと、エネルギーを失った荷電粒子をコレクタの前で阻止すること、アース電位(あるいはわずかにマイナス電位)の板を飛行領域近傍に設置して迷荷電粒子を吸収すること、などが行なわれる。機械的方法は、第2、4~8の実施形態(図5、9、10、11、13)で採用している。
精度を劣化させる要因は「飛行距離以外の真空度依存性」の存在であるが、その可能性と対策は以下にように考えられている。
[1]イオン引出し効率が変動する場合があり得るが、式(5)を使用することなどが対策となる。
[2]イオン開き角度が変動する場合があり得るが、アパーチャの設置やイオンビームよりも小さいコレクタの使用などによって検出角を制限しておくことが対策となる。これは第2、3、4~9の実施形態(図6、7、9~11、13~15)で採用している。
[3]分子との衝突以外にイオンのクーロン力発散(空間電荷効果)、中性分子の引き込みなどに要因があり得るが、これにはイオン電流を少なくする、イオンのエネルギーを高くする(イオン化が発生しない程度に)ことが対策となる。
後述する各実施形態にて説明する、平均自由行程を測定する装置1007は、図16に示す制御部1000を内蔵することができる。また、該制御部を、インターフェースを介して接続するようにしても良い。
図16において、符号1000は装置1007全体を制御する制御手段としての制御部である。この制御部1000は、種々の演算、制御、判別などの処理動作を実行するCPU1001、およびこのCPU1001によって実行される様々な制御プログラムなどを格納するROM1002を有する。また、制御部1000は、CPU1001の処理動作中のデータや入力データなどを一時的に格納するRAM1003、およびフラッシュメモリやSRAM等の不揮発性メモリ1004などを有する。
図5は本発明の第1の実施形態に係る平均自由行程を測定する装置1007を示す図であり、複合型のイオン源と透過型のコレクタが使用されている。図5で示されている装置1007全体が測定すべき雰囲気ガスの中に設置されている。ただし、図に示した電流計は模式的であって、実際には雰囲気ガスの外に配置されている。また、図には示されていないが、各電極は真空計としてよく知られている方法によって取付け・固定がなされ、接続された配線が大気側に導通している。たとえば、それぞれの電極は絶縁石(セラミックなど)にネジ止めされ、電気溶接された配線(ニッケル線など)がガラス封止の導入端子を経て大気側の制御装置まで伸びている。
すなわち、コレクタ203は、飛行距離L2飛行し減衰したイオン数Ibを検出する。
従って、不揮発性メモリ1004には、距離Lcの値(=0mm)も記憶されている。
まず、フィラメント101を加熱し、グリッドに到達する電子が適当な値となるように設定する(必ずしも、この値を正確に知る必要はなく、厳密に一定な値とする必要もない)。すなわち、制御部1000は、イオン源100からイオン110が発生するように、装置1007を制御する。
つぎに、内部コレクタ201、コレクタ202、コレクタ203に流れ込むそれぞれのイオンの量(イオン数Ic、イオン数Ia、イオン数Ib)を計測する。すなわち、制御部1000は、内部コレクタ201、コレクタ202、およびコレクタ203にてイオンを検出するように装置1007を制御し、検出されたイオン数Ic、イオン数Ia、イオン数Ibを装置1007から取得し、RAM1003に格納する。
最後に、取得されたイオン数Ic、イオン数Ia、イオン数Ibを適宜用い、式(3)~(5)を使って平均自由行程を算出するが、そのうちイオン量の比率が1.2倍から100倍の範囲内であれば確定値とする。すなわち、制御部1000は、平均自由行程の算出に用いる式に応じた情報を読み出して計算を行う。
イオン数IL1がイオン数Iaとなり、イオン数IL2がイオン数Ibとなり、飛行距離L1が距離Laとなり、飛行距離L2が距離Lbとなる。従って、制御部1000は、不揮発性メモリ1004から距離La、Lbを読み出し、RAM1003からイオン数Ia、Ibを読み出し、該読み出された値から式(5)に従って平均自由行程を算出する。
イオン数IL1がイオン数Icとなり、イオン数IL2がイオン数Iaとなり、飛行距離L1が距離Lcとなり、飛行距離L2が距離Laとなる。従って、制御部1000は、不揮発性メモリ1004から距離Lc、Laを読み出し、RAM1003からイオン数Ic、Iaを読み出し、該読み出された値から式(5)に従って平均自由行程を算出する。
減衰なし較正を行う場合は、制御部1000は、用いる式に応じて、不揮発性メモリ1004から初期値としてのイオン数Ia′、イオン数Ib′、イオン数Ic′を適宜読み出し、該読み出された値を用いて減衰なし較正を行うことができる。例えば、式(5)を用いる場合は、不揮発性メモリ1004からイオン数Ia′、イオン数Ib′を読み出し、イオン数Ia/イオン数Ia′およびイオン数Ib/イオン数Ib′に規格化して減衰なし補正を行う。
なお、制御部1000は、計算により得られた平均自由行程を表示部1006に表示させることができる。このように、表示することで、ユーザは現在の真空度を知ることができる。
図6は本発明の第2の実施形態に係る平均自由行程を測定する装置を示す図であり、複合型のイオン源と透過型コレクタとが使用されるとともに、迷イオンに対する対策とイオン開き角度による精度劣化の対策とが行なわれている。イオン源100とコレクタ-202とコレクタ203とは第1の実施形態と全く同じであり測定手順・計算方法・真空度範囲なども同じである。ただし、本実施形態では、機械的な迷イオン対策としてビーム角制限板400、迷イオン阻止板401a、401b(2枚)、迷イオン吸収板402の三種の電極が新たに設置されている。
以上、本実施形態では、迷イオン対策を厳重に行なって、測定精度の大幅な向上を可能にしている。
図7は本発明の第3の実施形態に係る平均自由行程を測定する装置を示す図であり、複合型のイオン源と透過型コレクタとが使用されるとともに、イオンの開き角度による精度劣化要因の対策、および電気的な迷イオンの対策が行なわれている。イオン源100とコレクタ202とコレクタ203とは第1の実施形態とほぼ同じであり測定手順・計算方法・真空度範囲なども同じであるが、コレクタ202、コレクタ203の大きさ(検出実効面)が特有なものとなっている。さらに、電気的な迷イオン対策としてイオンブランキングが新たに設置され、電流計としてロックイン(変調同期型)アンプが使用されている。
図8において、符号506は、雰囲気ガスと衝突しなかった時のコレクタにて検出されるイオン電流であり、符号507は、雰囲気ガスと衝突した時のコレクタにて検出されるイオン電流である。また、符号508は、信号となるイオン(無衝突でコレクタに到達したイオン)であり、符号509は、ノイズとなる迷イオンである。
図9は本発明の第4の実施形態に係る平均自由行程を測定する装置を示す図であり、装置としては測定のためのイオン源は保有せずに、プラズマなど測定すべき雰囲気から飛来するイオンを利用している。各電極に関しては第2の実施形態(図6)とほぼ同じで、装置1007は、迷イオン阻止板401a、401b、迷イオン吸収板402、およびシールドケース603を備えている。
図10は本発明の第5の実施形態に係る平均自由行程を測定する装置を示す図であり、本実施形態に係る装置1007は上記各実施形態に比べて真空度の悪い領域に適している。図10において、下側の図は正面図であり、上側の図は上面図である。透過型のコレクタ202は上記各実施形態と同じであるがイオン源100にはシンプルなものが使われ、全体に細長い形状としている。イオン源100は、SUS製などの板状(8mm×2mm程度。電子透過不可)のグリッド102、W製ワイヤ(φ0.2mm、長さ8mm程度)のフィラメント101のみを有している。なお、本実施形態のグリッドは、円筒型で電子を透過させ内部でイオンを生成させる第3の実施形態までのグリッドとは異なり、板状であってグリッド近傍でイオン化させるので電子を透過させる必要はなく、メッシュ//格子状ではなく目の詰った単なる板が使われる。グリッド102は+100V、フィラメント101は+30V程度に電圧が印加され、両者の間隔は1mm程度である。
図11Aは本発明の第6の実施形態に係る平均自由行程を測定する装置を示す図である。なお、図11Aの上側の図は、本実施形態に係る装置1007の上面図であり、下側の図は、正面図である。図11Bは、図11Aに示す装置1007のフィラメント・グリッドの制御回路を示す図である。本実施形態に係る装置1007は、より広範囲な測定が行なえるように測定に用いる荷電粒子をイオンと電子とで切り替え可能になっている。雰囲気内に設置する部分は印加電圧を除き第5の実施形態と同じであるが、フィラメント・グリッドの制御回路は新たなものとなっている。
図12Aは本発明の第7の実施形態に係る平均自由行程を測定する装置を示す図である。なお、図12Aの上側の図は、本実施形態に係る装置1007の上面図であり、下側の図は、正面図である。図12Bは、図12Aに示す装置1007のフィラメントの制御回路を示す図である。本実施形態に係る装置1007は、電子専用として構造をよりシンプルにするとともに同じフィラメント101を使ってピラニゲージの機能を持たせている。雰囲気内に設置する部分はグリッドが存在しないことを除き第6の実施形態と同じであるが、図12Bに示すように、フィラメントの制御回路は新たなものとなっている。電子310による平均自由行程の測定の動作・手順は第6の実施形態と全く同じであり、必要に応じ「減衰なし較正」「真空計較正」を行なうことも同様である。
図13Aは本発明の第8の実施形態に係る平均自由行程を測定する装置を示す図である。なお、図13Aの上側の図は、本実施形態に係る装置1007の上面図であり、下側の図は、正面図である。図13Bは、図13Aに示した装置の各電極の形状を示す図であり、図13Cは、図13BにおけるラインAでの電子ビーム軌道を示す図であり、図13Dは、図13BにおけるラインBでの電子ビーム軌道を示す図である。本実施形態に係る装置1007では、幅(面積)が広い電子源の使用および「減衰なし較正」無しに対応できるようにコレクタの形状を工夫している。これはつぎのような要求によるものである。1800℃もの高温になるフィラメント方式では雰囲気ガスと反応してしまうなどの問題があり、より低温にできる傍熱型の酸化物陰極やその他低温の電子源が望まれている。しかしながら、このような電子源は輝度(電子の強度。単位面積、単位角度あたりの電子放出量)が大幅に低くなってしまう。また、用途によっては雰囲気の真空度を十分に良くすることは不可能で「減衰なし較正」を使用できない場合がある。
ビーム角制限板400、コレクタ202、コレクタ203、迷電子吸収板412はいずれも厚み0.5mm程度のSUS製などの板(プレート)である。電子源300の電位は-30Vであり、迷電子吸収板412は+5Vとしているが、その他はすべてアース電位(0V)となっている。
図14Aは本発明の第9の実施形態に係る平均自由行程を測定する装置を示す図である。なお、図14Aの上側の図は、本実施形態に係る装置1007の上面図であり、下側の図は、正面図である。図14Bは、図14Aに示す各電極の形状、およびそれらの回路を示す図である。本実施形態に係る装置1007では、幅広の電子源と「減衰なし較正」無しの実現とに加え、多くのコレクタを使用することにより適用真空度の範囲を拡大している。基本的な構造・動作は第8の実施形態の図13と同じであるが、コレクタの数が増加するとともにロックイン(変調同期型)アンプ502が使われている。よって、本実施形態では、迷電子吸収板を用いる必要が無い。
図15Aは本発明の第10の実施形態に係る平均自由行程を測定する装置を示す図であり、図15Bは、図15AのA-A′線断面図である。本実施形態では、1つのコレクタにてしかも機械的な構造も変えずに、異なる飛行距離の測定が行なえるようにしている。
距離を変更する原理は、進行方向(軸方向)に平行な磁場が存在すると電子はらせん運動を行なうこと、らせん回数は進行方向の速度(運動エネルギー)に依存することに拠っている。利用する荷電粒子はイオンでも可能であるが、強力な磁場が必要でガス種によりらせん運動(径)が変わることなどの問題があるので、本実施形態では電子を使用している。
前者をリペラ兼用磁石701とし、後者をコレクタ兼用磁石702とする。両者の間隔は80mm程度であり、その間の磁場が16ガウスとなるように調整されている。
シールドケース603は厚みが5mm程度の純鉄(あるいは磁性ステンレス)製で、外乱磁場のシールド(遮蔽)だけでなく磁石のヨークの役目を果たす。
以上各実施形態を説明してきたが、本発明の実施形態はこれらに限定されることはなく、それぞれの実施形態の各要素を組み合わせること、入れ替えることが可能なのは当然である。また、全体の構造、およびそれぞれの電極の形状、寸法、材料、および印加電圧は上記実施形態に限定されることなく任意に選ぶことができる。
項目15)「精度劣化の要因」にて上述したように、理想的な状態からの“ずれ”は必ず発生するものであるが、関連する条件(イオン電流、イオンエネルギー、イオン種など)が同じであれば“ずれ”もほぼ同じであることが多い。そこで、実験的(経験的)にこの“ずれ”を測定し、これを補正するような計算式、すなわち実験式(補正項)を入れた計算式を求めておくことが出来る。この実験式(例えば、乗算に関する実験式F、および加算に関する実験式G)を入れた計算式(例えば、λ=(L2-L1)/In(IL1/IL2)×F+G)によるプログラムを使用することによって、より精度の高い測定を行なうことが出来る。また、さらに、補正項は関連する条件に依存するので、いくつかの条件での実験を行なうことにより、関連する条件を変数とした補正項の関数(例えば、実験式F、G)を求めることが可能となる。これを使用すると、さらに精度のよい測定を行うことができる。
本発明は、複数の機器(例えばコンピュータ、インターフェース機器、リーダ、プリンタ、装置1007など)から構成されるシステムに適用することも、1つの機器からなる装置に適用することも可能である。
Claims (19)
- 雰囲気ガス中における荷電粒子の平均自由行程を測定する装置であって、
前記荷電粒子を発生する発生源と、
前記発生源からの飛行距離が0以上の第1の飛行距離である荷電粒子の第1の荷電粒子数を検出し、前記第1の飛行距離よりも長い第2の飛行距離の荷電粒子の第2の荷電粒子数を検出する検出手段と、
前記第1および第2の荷電粒子数の比率から前記平均自由行程を算出する算出手段と
を備えることを特徴とする装置。 - 前記検出手段は、
前記第1の荷電粒子数を検出する第1の検出器と、
前記第1の検出器よりも前記発生源から遠い距離に位置する、前記第2の荷電粒子数を検出する第2の検出器と
を有することを特徴とする請求項1に記載の装置。 - 前記検出手段は、
前記荷電粒子を検出する検出器と、
前記発生源から前記検出器までの前記荷電粒子の軌道を調整する調整手段とを有し、
前記調整手段により前記荷電粒子の飛行距離を変化させることにより、前記検出器は前記第1及び第2の荷電粒子数を検出することを特徴とする請求項1に記載の装置。 - 前記発生源は、
電子を放出させるフィラメントと、
前記電子を引き寄せて前面近傍でイオンを生成させるグリッドと、
前記生成されたイオンを引き出す平板状の引出し電極であって、到達したイオンのうちその一部のイオンをそのまま通過させるように構成された引出し電極と
を有することを特徴とする請求項1に記載の装置。 - 前記発生源は、
電子を放出させる電子源と、
前記放出された電子を引き出す引出し電極であって、到達した電子のうちその一部の電子をそのまま通過させるように構成された引出し電極と
を有することを特徴とする請求項1に記載の装置。 - 前記荷電粒子は、イオンであり、
前記発生源は、
熱電子を放出させるフィラメントと、
前記熱電子を引き込み内部でイオンを生成させる略円筒状のグリッドと、
前記グリッドの内部に設置されたワイヤ状のコレクタとを有し、
前記コレクタの長さを前記グリッドの軸方向長さより短くしたことを特徴とする請求項1に記載の装置。 - 前記コレクタの長さは、前期グリッドの軸方向長さの半分程度であることを特徴とする請求項6に記載の装置。
- 第1の真空度において検出された第1の荷電粒子数を第1の初期値とし、該第1の真空度において検出された第2の荷電粒子数を第2の初期値とした時、前記算出手段は、前記第1の真空度よりも悪い第2の真空度において検出された第1の荷電粒子数を、該第1の荷電粒子数を前記第1の初期値で割った値に規格化し、かつ前記第2の真空度において検出された第2の荷電粒子数を、該第2の荷電粒子数を前記第2の初期値で割った値に規格化して、前記第1および第2の荷電粒子数の比率を求めることを特徴とする請求項1に記載の装置。
- 前記検出手段は、到達した荷電粒子のうちその一部を検出するとともに、他の一部の荷電粒子をそのまま通過させるように構成された検出器であることを特徴とする請求項1に記載の装置。
- 前記構成された検出器は、少なくとも1つの開口部を有し、
前記少なくとも1つの開口部を有する検出器は、メッシュ状、スリット状、または少なくとも1つの窓を有する検出器であることを特徴とする請求項9に記載の装置。 - 雰囲気ガスと衝突して運動エネルギーを失った荷電粒子を吸収する電極をさらに備えることを特徴とする請求項1に記載の装置。
- 検出器に到達する荷電粒子を断続的とする手段と、
前記手段と同期したロックイン(変調同期型)アンプとをさらに備え、
前記ロックインアンプは、前記検出された第1および第2の荷電粒子数からノイズを除去することを特徴とする請求項1に記載の装置。 - 前記荷電粒子を発生する発生源として雰囲気ガス中に存在するプラズマを利用することを特徴とする請求項1に記載の装置。
- 前記発生源は、発生される荷電粒子としてイオンと電子を切り替え可能であることを特徴とする請求項1に記載の装置。
- 前記算出された平均自由行程から該平均自由行程に対応する圧力に変換する手段と、
前記変換された圧力を表示する手段と
をさらに備えることを特徴とする請求項1に記載の装置。 - 雰囲気ガス中における荷電粒子の平均自由行程を測定する方法であって、
前記荷電粒子を発生源から発生させる工程と、
前記発生源からの飛行距離が0以上の第1の飛行距離である荷電粒子の第1の荷電粒子数を検出し、前記第1の飛行距離よりも長い第2の飛行距離の荷電粒子の第2の荷電粒子数を検出する工程と、
前記第1および第2の荷電粒子数の比率から前記平均自由行程を算出する工程と
を有することを特徴とする方法。 - 前記荷電粒子はイオンであり、
前記荷電粒子を発生源から発生させる工程は、
前記発生源が有するフィラメントに第1の電位を印加し、前記発生源が有するグリッドに前記第1の電位よりも高い第2の電位を印加して、前記フィラメントから放出された電子を前記グリッドに引き寄せて、該グリッド近傍でイオンを生成し、前記発生源が有する平板状の引出し電極であって、到達したイオンのうちその一部のイオンをそのまま通過させるように構成された引出し電極に前記第2の電位よりも低い第3の電位を印加して、前記生成されたイオンを前記引出し電極に引き寄せ、該引き寄せられたイオンの一部を前記引出し電極から透過させることを特徴とする請求項16に記載の方法。 - 前記荷電粒子は電子であり、
前記荷電粒子を発生源から発生させる工程は、
前記発生源が有するフィラメントに第1の電位を印加して該フィラメントから電子を発生させ、前記発生源が有する平板状の引出し電極であって、到達した電子のうちその一部の電子をそのまま通過させるように構成された引出し電極に前記第1の電位よりも高い第2の電位を印加して、前記生成された電子を前記引出し電極に引き寄せ、該引き寄せられた電子の一部を前記引出し電極から透過させることを特徴とする請求項16に記載の方法。 - 請求項1に記載の装置を備える真空容器であって、
前記真空容器内にプラズマを生成する手段をさらに備え、
前記発生源として、前記生成されたプラズマを用いることを特徴とする真空容器。
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KR101296275B1 (ko) | 2013-08-14 |
CN102630298B (zh) | 2014-08-13 |
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US20120235034A1 (en) | 2012-09-20 |
CN102630298A (zh) | 2012-08-08 |
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JPWO2011033933A1 (ja) | 2013-02-14 |
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