JP2016001555A - Gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas analyzer capable of preventing contamination due to fluorine with respect to an ion source even in the presence of fluorine and keeping the measurement sensitivity and operable time for a long time.SOLUTION: Disclosed is a gas analyzer 100 which is equipped with an ion box 11 inside which sample gas is introduced, and analyzes the sample gas ionized in the ion box 11. The ion box 11 is formed by specific metal and fluoride of the specific metal is gas under measurement conditions of the gas analyzer.

Description

  The present invention relates to a gas analyzer that ionizes and analyzes a sample gas in the presence of fluorine.

  For example, in a semiconductor manufacturing apparatus, the amount of gas remaining in a process chamber is measured, and maintenance and quality control are performed. For this purpose, a gas analyzer (see Patent Document 1) that introduces a sample gas from the process chamber and ionizes and analyzes the sample gas in an ion source is used.

  By the way, when the gas analyzer is used in the presence of fluorine, the time until the measurement sensitivity is lowered to the extent that the measurement accuracy is affected, and the time until the ion source becomes physically inoperable There is a problem that it becomes shorter than in the environment.

  As a result of intensive studies by the inventors of the present invention on the cause of this problem, the ion box is formed of, for example, Inconel (registered trademark) made of nickel, iron, or the like, and a sample gas is introduced therein, and the ion box It has been found for the first time that the following phenomenon occurs in the ion source including a filament that injects free electrons into the sample gas and ionizes the sample gas.

  That is, in the presence of fluorine, nickel and fluorine forming the ion box react to form a fluoride film on the surface, and this film is a non-conductor, so the free electrons emitted from the filament Will be charged.

  For this reason, the potential of the ion box is lower than when the ion box is used in a normal use environment, and free electrons emitted from the filament are less likely to be introduced into the ion box.

  Then, the amount of ionized sample gas is reduced, and the amount of sample gas ions detected by a detector such as a Faraday cup is also reduced, resulting in a decrease in sensitivity.

  Furthermore, the gas analyzer increases the voltage applied to the filament and increases the amount of emitted free electrons when a decrease in potential or sensitivity in the ion box is detected. It is configured. For this reason, when a fluoride film is formed in the ion box, the potential of the ion box decreases and the sensitivity also decreases, the voltage applied to the filament increases. Therefore, the load applied to the filament is increased in a shorter time than designed, and as a result, it is considered that the time until the filament is broken and becomes inoperable is shortened.

Japanese Patent Laid-Open No. 9-320517

  The present invention has been made in view of the above-described problems. A gas analyzer that can prevent the ion box from being contaminated by fluorine even in the presence of fluorine and can achieve a long life while maintaining measurement sensitivity. The purpose is to provide.

  That is, the gas analyzer of the present invention is a gas analyzer that includes an ion box into which a sample gas is introduced and analyzes the sample gas ionized in the ion box, and the ion box includes a specific metal. The fluoride of the specific metal is a gas under the measurement conditions of the gas analyzer.

  In such a case, even when used in the presence of fluorine, the active species containing fluorine element reacts with the specific metal forming the ion box and is vaporized, so that a nonconductive film is formed in the ion box. Such contamination by fluorine can be prevented.

  Therefore, even in the presence of fluorine, the potential drops in the ion box, making it difficult for free electrons or ions to ionize the sample gas to be introduced. However, it is difficult for a decrease to occur.

  For example, when the gas analyzer measures a residual gas in a process chamber of a semiconductor manufacturing apparatus, a gas analyzer suitable for preventing a reduction in sensitivity and a shortening of the product life can be used. Any substance that vaporizes at a predetermined degree of vacuum may be used.

  In order to make it easy to form the three-dimensional shape of the ion box by a simple process such as bending, and to reduce the manufacturing cost while minimizing the amount of the specific metal used, the ion box has the specific What is necessary is just to be formed by plating a base material made of a metal other than a metal with the specific metal.

  The ion box is an ionized sample as an effective plating point for preventing the decrease in sensitivity due to the contamination of the ion box with fluorine and extending the time until the filament becomes disconnected and becomes inoperable. It is comprised from the bottom member which makes the bottom face by the side of the detection part which detects gas, and the top member which makes an upper surface and a side surface, The inside of the said top member is what is plated with the said specific metal at least.

  To prevent the gas analyzer from decreasing in sensitivity and shortening its service life even when fluorine is present, it is possible to realize ease of plating, ease of processing after plating, etc. The specific metal may be platinum.

  If the ion box and a filament that emits free electrons to the ion box constitute an ion source, and the filament does not contain tungsten and is formed of rhenium, even in the presence of fluorine, It is possible to realize a longer life by preventing the filament from thinning and breaking in a short time by reacting with fluorine.

  As a specific embodiment of the gas analyzer, a mass separation unit that separates ions of the sample gas ionized by the ion source according to a ratio of charge to mass, and ions that have passed through the mass separation unit What further has a detection part to detect is mentioned.

  Thus, according to the gas analyzer of the present invention, since the ion box is formed of a specific metal that reacts with an active species derived from elemental fluorine and vaporizes under measurement conditions, A non-conductive film is not formed even underneath, and it is possible to prevent a decrease in sensitivity and a shortened life due to this non-conductive film.

The schematic diagram which shows the use application of the gas analyzer which concerns on one Embodiment of this invention. The schematic diagram which shows the gas analyzer which concerns on the same embodiment. The typical perspective view which shows the detail of the gas analyzer in the same embodiment. The schematic diagram which shows the structure of the ion box in the embodiment. The typical graph which shows the lifetime test result in the fluorine atmosphere in the conventional gas analyzer, and a sensitivity test result. The typical graph which shows the lifetime test result in the fluorine atmosphere of the gas analyzer of the same embodiment, and a sensitivity test result.

  A gas analyzer 100 according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the gas analyzer 100 of the present embodiment is a residual gas that measures the partial pressure of the residence gas in the process chamber C in which a semiconductor, a liquid crystal panel, a solar cell, etc. are formed in a semiconductor manufacturing apparatus 200 It is an analyzer (RGA). Here, the process chamber C is a room whose pressure is reduced to a predetermined degree of vacuum.

  As shown in FIG. 1, the gas analyzer 100 is a gas analyzer 100 that analyzes an ionized sample gas, and includes a sensing mechanism SN inserted into the process chamber C and an outside of the process chamber C. The operation display unit D is provided. Here, the analysis is a concept including measuring the amount and concentration of ions and detecting the presence or absence of ions.

  The sensing mechanism SN forms a quadrupole mass separator as shown in the schematic diagram of FIG. 2 and the detailed view of FIG. 3, and includes an ion source 1 in which the sample gas in the process chamber C is ionized, and an ion The mass separation unit 2 is configured to perform mass separation, and the detection unit 3 detects ions that have passed through the mass separation unit 2 as current. The operation display unit D calculates, for example, partial pressures of oxygen, nitrogen, and water related to the quality control of film formation based on the current detected by the detection unit 3, and displays the change with time. In the process chamber C, there is also fluorine introduced as a component gas or the like for film formation although it is kept in a substantially vacuum.

  The ion source 1 includes an ion box 11 into which a sample gas is introduced, and a filament 12 that emits free electrons to the ion box 11.

  The ion box 11 (ionization chamber, ionization part) is formed in a substantially flat hexagonal column shape as shown in FIG. 3, and a box body in which openings for introducing sample gas and free electrons are formed on each surface. And the sample gas is ionized therein. The ion box 11 has a surface plated with an alloy such as Inconel containing iron and nickel as a base material. As shown in FIGS. 4A and 4B, the ion box 11 includes a bottom member 11a that forms a bottom surface on the detection unit 3 side that detects ionized sample gas, and a top member 11b that forms an upper surface and side surfaces. It is composed of. As shown in FIG. 4A, the bottom member 11a is formed by bending a part of a flat base material after plating. Further, as shown in FIG. 4B, the top member 11b is formed in a flat hexagonal columnar shape by bending each side surface portion after plating a flat base material. And as shown in FIG.4 (c), the said ion box 11 is formed by attaching the said bottom member 11a to the bottom face of the said top member 11b.

  More specifically, the ion box 11 reacts with an active species containing a fluorine element (for example, F +, fluorine atom, fluorine molecule, fluorine ion, etc.) to generate gaseous fluoride under the measurement conditions of the gas analyzer 100. It is made of a specific metal that is a metal to be formed. Here, the measurement conditions of the gas analyzer 100 refer to conditions such as temperature and pressure suitable for ionizing the sample gas, for example. In addition, being formed of a specific metal is a concept including at least that the entire ion box is formed of a specific metal, formed of an alloy containing the specific metal, and plated with the specific metal. is there. In the present embodiment, the ion box 11 is plated with a specific metal.

  That is, the ion box 11 is plated with a specific metal that reacts with fluorine to form a fluoride having a boiling point equal to or lower than a predetermined temperature. Here, the boiling point equal to or lower than a predetermined temperature refers to, for example, a boiling point of a fluorine compound in a standard state that is equal to or lower than a predetermined threshold value. The threshold is set based on the room temperature of the room in which the process chamber C is placed, the temperature in the process chamber C, and the like. In the present embodiment, 69.1 ° C., which is the boiling point of platinum hexafluoride in the standard state, is determined as the threshold value. In addition, as the specific metal for plating the ion box 11, a metal that is vaporized by the degree of vacuum in the environment in which it is used is selected. In the present embodiment, the ion box 11 is made of platinum (Pt) plated on a base material in order to prevent a long life and a decrease in sensitivity, which will be described later, and to make the bending process easy.

  The filament 12 does not contain tungsten (W) and is formed of rhenium (Re). The voltage applied to the filament 12 is configured to be feedback-controlled based on the current value output from the detection unit 3 so that the ionization capability of the sample gas per unit time is kept substantially constant. It is. That is, when the ionization capacity in the ion box 11 is lowered, the voltage automatically applied increases, and this voltage control is continued until the filament 12 is finally cut. is there.

  The mass separation unit 2 includes four parallel rod-shaped electrodes, and forms a quadrupole electric field by applying a voltage in which a DC voltage and a high-frequency AC voltage are superimposed with the same polarity of the opposite rod-shaped electrodes. It is what you do. In this quadrupole electric field, only oxygen ions and hydrogen ions to be analyzed among the ions incident from the ion source 1 pass to the detection unit 3, and other ions having a charge / mass ratio are rod-shaped electrodes. So as not to pass through the detection unit 3 due to collision with the sensor.

  The detection unit 3 includes a Faraday cup and outputs a current corresponding to the number of incident ions and their charges. The output current value is converted by the operation display unit D by a predetermined calculation and used to calculate the presence of residual gas and its partial pressure.

  An ion box formed of inconel and not plated and an alloy of tungsten and rhenium with respect to the life extension effect and the sensitivity reduction prevention effect in the presence of fluorine by the gas analyzer 100 of the present embodiment configured as described above. The conventional gas analyzer provided with the filament formed in the above and the gas analyzer 100 of the present embodiment will be described in comparison. The graph of FIG. 5 is the result of the life test and sensitivity test in the conventional gas analyzer, and the graph of FIG. 6 is the result of the life test and sensitivity test in the gas analyzer 100 of this embodiment. In both comparative experiments, the measurement object is sulfur hexafluoride (SF6), and fluorine is present around the sensing mechanism. Further, the lifetime is determined by monitoring the current and voltage applied to the filament and determining when the measured value cannot be detected due to the filament being cut. Regarding the sensitivity reduction, when the same amount of ions are incident on the detection unit 3, it is determined that the sensitivity reduction has occurred because the order of the current value output from the detection unit 3 has decreased by one digit.

  In the conventional gas analyzer, when fluorine exists around the sensing mechanism, as shown in FIG. 5 (a), the filament breaks after 60 hours and reaches the end of its life. Further, as shown in FIG. 5B, the sensitivity is lowered after 20 hours.

  On the other hand, in the gas analyzer 100 of the present embodiment, the filament 12 is not broken until 120 hours have elapsed as shown in FIG. 6A, and the filament 12 has no breakage as shown in FIG. 6B. Until the disconnection, the sensitivity is kept substantially constant.

  That is, as can be seen from the comparison between FIG. 5 and FIG. 6, in the gas analyzer 100 of this embodiment, the ion box 11 is plated with platinum, and the filament 12 does not contain tungsten. As a result, it is possible to extend the life even in the presence of fluorine, and to prevent a substantial decrease in sensitivity until the end of the life.

  This difference in lifetime and sensitivity is considered to be due to the following phenomenon. In the ion box of a conventional gas analyzer, when fluorine is present, a non-conductive film is formed on the surface by nickel forming the ion box, free electrons are charged in the non-conductive film, and free electrons are introduced into the ion box. It becomes difficult to be done. As a result, an excessive voltage is continuously applied to the filament so that the ionization ability of the sample gas is maintained, which causes the filament to break in a short time. In addition, since the ionization ability of the sample gas is reduced, the sensitivity is also reduced.

  On the other hand, in the gas analyzer 100 of the present embodiment, the platinum plating the ion box 11 reacts with fluorine to form a fluoride and vaporizes immediately. A nonconductive film is not formed on the surface of the box 11. This makes it possible to extend the life and maintain sensitivity even in the presence of fluorine.

  In addition, since the filament 12 of this embodiment does not contain tungsten that reacts with fluorine and vaporizes, the filament 12 can be prevented from rapidly thinning even in the presence of fluorine. This also contributes to extending the life of the gas analyzer 100 of the present embodiment.

  Other embodiments will be described.

  In the embodiment, platinum is plated on the surface of the ion box, but the ion box may be plated with a specific metal that forms a fluoride that reacts with other fluorine to vaporize at a predetermined temperature or lower. I do not care.

  As the specific metal for plating the ion box, any of transition metals such as molybdenum (Mo), tungsten (W), iridium (Ir), rhenium (Re), and technetium (Tc) can be used. Since these specific metal fluorides have a boiling point lower than that of platinum hexafluoride, which is a compound of platinum and fluorine, and are vaporized, the same effects as in the above embodiment can be obtained. Moreover, you may plate with these specific metals and multiple types of specific metals instead of platinum simple substance. In addition, a typical metal may be used as long as it is a metal that forms a gaseous fluoride under the measurement conditions of the gas analyzer.

  In addition, the metal forming the ion box may be selected so as to prevent elements other than fluorine from forming a non-conductive film on the ion box. In this case, the ion box may be formed of a metal that reacts with an element other than fluorine to form a gaseous compound under the measurement conditions of the gas analyzer.

  The entire surface of the ion box may not be plated with a specific metal, and only needs to be at least partially plated. For example, if the inner surface side of the ion box is plated with a specific metal, the effect of prolonging the life and preventing the sensitivity from being lowered can be obtained. More specifically, it is sufficient that at least the inside of the top member is plated with a specific metal. Further, a part of the ion source may be plated with a specific metal. The base material of the ion box is not limited to Inconel, but may be other alloys. The effect of the present invention becomes remarkable when the composition of the base material of the ion box includes one that forms a fluoride that does not vaporize by reacting with fluorine.

  Further, the ion box itself may be formed of a specific metal or an alloy containing the specific metal. In this case, it is sufficient that the specific metal is on the surface of the ion box and can contact and react with elemental fluorine or ions derived from elemental fluorine.

  For the filament, an alloy of tungsten and rhenium may be used, and the gas analyzer may be configured by plating the ion box with a specific metal that forms a fluoride that easily vaporizes by reacting with fluorine.

  In the above embodiment, the sample gas is ionized by free electrons, but the sample gas may be ionized by, for example, ions or radiation. Moreover, as a gas analyzer, you may use structures other than the mass separation part shown in embodiment, and a detection part. Further, the gas analyzer may be used not only for the residual gas analyzer but also for other purposes. In short, any gas analyzer that analyzes the sample gas ionized by the ion source can enjoy the effects of the present invention.

  In addition, various modifications and combinations of the embodiments may be made without departing from the spirit of the present invention.

200 ... Semiconductor manufacturing apparatus 100 ... Gas analyzer (RGA)
DESCRIPTION OF SYMBOLS 1 ... Ion source 11 ... Ion box 12 ... Filament 2 ... Mass separation part 3 ... Detection part

Claims (7)

A gas analyzer comprising an ion box into which a sample gas is introduced, and analyzing the sample gas ionized in the ion box,
The ion box is made of a specific metal;
The gas analyzer is characterized in that the fluoride of the specific metal is a gas under the measurement conditions of the gas analyzer.   The gas analyzer according to claim 1, wherein the fluoride of the specific metal is vaporized at a predetermined degree of vacuum.   The gas analyzer according to claim 1 or 2, wherein the ion box is formed by plating a base material formed of a metal other than the specific metal with the specific metal. The ion box includes a bottom member that forms a bottom surface on the detection unit side that detects ionized sample gas, and a top member that forms an upper surface and a side surface.
The gas analyzer according to claim 3, wherein an inner side of the top member is plated with at least the specific metal.   The gas analyzer according to claim 1, wherein the specific metal is platinum. The ion box and a filament that emits free electrons to the ion box constitute an ion source,
The gas analyzer according to claim 1, wherein the filament does not contain tungsten and is formed of rhenium. A mass separation unit that separates ions of the sample gas ionized by the ion source according to a ratio of charge to mass;
The gas analyzer according to claim 1, further comprising: a detection unit that detects ions that have passed through the mass separation unit.