News Column

Patent Issued for Mass Flow Controller Verifying System, Verifying Method and Verifying Program

February 26, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- Horiba STEC, Co., Ltd. (Kyoto-shi, JP) has been issued patent number 8646307, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Yasuda, Tadahiro (Kyoto, JP); Yamaguchi, Yuji (Kyoto, JP).

This patent was filed on February 27, 2013 and was published online on February 11, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "The present invention generally relates to a mass flow controller verifying system, and in particular to a method of verifying a mass flow controller in a gas piping system having a plurality of influent flow gas lines including mass flow controllers arranged in parallel, wherein the influent flow gas lines are joined together to form one post-confluent flow gas line.

"In order to supply a mixed gas to a process chamber in a process of manufacturing a semiconductor and the like, there is constituted a gas piping system that comprises a plurality of influent flow gas lines arranged in parallel, each having a mass flow controller, the influent flow gas lines being connected to a gas supply source and the influent flow gas lines being joined together to form one post-confluent flow gas line connected to the process chamber.

"In a gas piping system as mentioned above, Patent Literature 1 (reference JP2007-525726A) discloses a diagnostic system for verifying whether or not a mass flow controller provided on each of the influent flow gas lines can execute a flow rate control accurately, as defined to be in conformity with a preset flow rate.

"In this system, as shown in FIG. 1, a branch flow line BL is formed to be connected in parallel to a post-confluent flow gas line ML, a large-capacity chamber A1 having a prescribed volume is provided on the branch flow line BL, and a pressure sensor A2 is provided on a downstream side thereof. Thus, the verifying of the mass flow controller 1 is performed based on a pressure measured by the pressure sensor A2. Further, in the post-confluent flow gas line ML, there are provided open-close (opening/closing) valves between the connecting points of the branch flow line BL and in the vicinities of the inlet and outlet of the branch flow line BL, respectively.

"By this verifying system A100, a mass flow controller verifying method referred to as a rate of rise (ROR) system is used. Referring to a verifying procedure thereof specifically, when a mass flow controller is verified, only an open-close valve on the inlet side of the branch flow line is opened while the other valves are closed, and the influent gas lines SL, except for an influent flow gas line SL having a target mass flow controller 1 to be verified, are also closed. Then, a prescribed set flow rate is set to the target mass flow controller 1 to be verified so as to introduce a gas into the chamber and increase the pressure. Meanwhile, the change in pressure is measured by the pressure sensor, and a verifying volume corresponding to the volume of the chamber A1 is calculated based on the rate of pressure change. Subsequently, the calculated verifying volume is compared to a reference volume that is a sum of the prescribed known chamber volume and an approximate rough volume of a piping portion from the target mass flow controller to the chamber. In this comparison, when the calculated verifying volume is equal to the reference volume, it is judged that the mass flow controller can execute a flow rate control as defined to be in conformity with the set flow rate. When the calculated verifying volume is not equal to the reference volume, it is judged that the mass flow controller cannot execute a flow rate control as defined to be in conformity with the set flow rate due to clogging and so forth.

"However, in the mass flow controller verifying system as disclosed in Patent Literature 1, some problems are involved as described below.

"In order to introduce this verifying system into an existing gas piping system for use in a semiconductor manufacturing process and so forth, it is necessary to newly constitute piping, such as a branch flow line connected to a post-confluent piping, and to provide a chamber for obtaining a reference volume. In some cases, however, it may be difficult to newly provide an additional piping and chamber due to a layout of a factory and the like, and due to the resulting increased costs for designing the piping for the verifying system to fit to the existing piping system and installing of the new piping and chamber.

"In order to verify a mass flow controller accurately according to the methods of an ROR system and the like, it is necessary to confirm the reference volume correctly. In this verifying system, the sum of the piping volume in a region from a target mass flow controller to be verified to the chamber and the known volume of the chamber is used as the reference volume, and the piping volume is usually roughly calculated based on, e.g., a length of the corresponding piping. However, it is difficult to accurately calculate a volume of a curved portion of a piping and a volume inside an open-close valve and so forth, and therefore the calculated value of the reference volume is not very reliable. Moreover, if it is intended to be able to absorb an error related to such a piping volume, the volume of the chamber should be increased to a certain extent.

"If the volume of the chamber is increased to be large or the reference volume is large, an amount of a pressure change required for verifying cannot be measured without a necessary long time lapse. Therefore, it takes a long time to verify each of the mass flow controllers."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "The present invention has been made to solve the above problems, and therefore an object of the present invention is to provide a verifying system that can be introduced into an existing gas piping system used in a semiconductor manufacturing process and so forth at a low cost without any change in designing a piping and the like, and that is capable of verifying a mass flow controller based on an accurate reference volume in a short time.

"Accordingly, a first aspect of the present invention provides a mass flow controller verifying system for use in a gas piping system provided with one or a plurality of influent flow gas lines each having a mass flow controller and provided with a post-confluent flow gas line into which a plurality of gas lines including the influent flow gas lines are joined wherein the post-confluent flow gas line is provided with a post-confluent valve thereon after the confluence of the plurality of gas lines. The verifying system comprises: a verifying gas line provided with a flow rate measurement unit adapted to measure a flow rate of a gas, a flow rate adjustable valve by which an opening degree thereof is adjusted so that the measurement flow rate measured by the flow rate measurement unit is coincident with a set flow rate, and a pressure measurement unit adapted to measure a gas pressure, wherein the verifying gas line is arranged in parallel to the influent flow gas lines and joined into the post-confluent flow gas line; a reference volume calculating portion adapted to calculate a reference volume based on time series data of a measurement pressure measured by the pressure measurement unit, wherein the reference volume is a volume inside a piping portion determined by the flow rate adjustable valve, a closing position of each of the influent gas lines and the post-confluent valve, in a state that each of the influent gas lines is closed and the post-confluent valve is closed; a verifying parameter calculating portion adapted to calculate a verifying parameter based on the time series data of the measurement pressure measured by the pressure measurement unit in a state that the influent gas lines, except for an influent gas line having a target mass flow controller to be verified, are closed at the same position as the closing position in the calculation of the reference volume and that the adjustable valve and the post-confluent valve are closed; and a comparing portion adapted to compare a reference parameter set based on the reference volume and the verifying parameter.

"A second aspect of the present invention provides a mass flow controller verifying method for use in a gas piping system provided with one or a plurality of influent flow gas lines each having a mass flow controller and provided with a post-confluent flow gas line into which a plurality of gas lines including the influent flow gas lines are joined wherein the post-confluent flow gas line is provided with a post-confluent valve thereon after the confluence of the gas lines. The verifying method comprises: a step of installing a verifying gas line arranged in parallel to the influent flow gas lines and joined into the post-confluent flow gas line, wherein the verifying gas line is provided with a flow rate measurement unit adapted to measure a flow rate of a gas flowing through the verifying gas line, a flow rate adjustable valve by which an opening degree thereof is adjusted so that the measurement flow rate measured by the flow rate measurement unit is coincident with a set flow rate, and a pressure measurement unit adapted to measure a gas pressure in the verifying gas line; a step of calculating a reference volume based on time series data of a measurement pressure measured by the pressure measurement unit, wherein the reference volume is a volume inside a piping portion determined by the flow rate adjustable valve, a closing position of each of the influent gas lines and the post-confluent valve, in a state that each of the influent gas lines is closed and the post-confluent valve is closed; a step of calculating a verifying parameter based on the time series data of the measurement pressure measured by the pressure measurement unit in a state that the influent gas lines, except for an influent gas line having a target mass flow controller to be verified, are closed at the same position as the closing position in the calculation of the reference volume and that the adjustable valve and the post-confluent valve are closed; and a step of comparing a reference parameter set based on the reference volume and the verifying parameter.

"A third aspect of the present invention provides a computer readable program for use in verifying a mass flow controller in a gas piping system provided with one or a plurality of influent flow gas lines each having a mass flow controller and provided with a verifying gas line in parallel to the influent flow gas lines, wherein the verifying gas line is provided with a flow rate measurement unit adapted to measure a flow rate of a gas, a flow rate adjustable valve by which an opening degree thereof is adjusted so that the measurement flow rate measured by the flow rate measurement unit is coincident with a set flow rate, and a pressure measurement unit adapted to measure a gas pressure, wherein a post-confluent flow gas line located after the confluence of each of the influent gas lines and the verifying gas line is provided with a post-confluent valve thereon. The computer readable program executes the processes of; calculating a reference volume based on time series data of a measurement pressure measured by the pressure measurement unit, wherein the reference volume is a volume inside a piping portion determined by the flow rate adjustable valve, a closing position of each of the influent gas lines and the post-confluent valve, in a state that each of the influent gas lines is closed and the post-confluent valve is closed; setting a set flow rate to a target mass flow controller to be verified and to calculate a verifying parameter based on the time series data of the measurement pressure measured by the pressure measurement unit during the flow rate control executed by the target mass flow controller to be verified in a state that the influent gas lines, except for an influent gas line having a target mass flow controller to be verified, are closed at the same position as the closing position in the calculation of the reference volume and that the adjustable valve and the post-confluent valve are closed; and comparing a reference parameter set based on the reference volume and the verifying parameter.

"According to these aspects of the present invention, in an existing gas piping system for use in a semiconductor manufacturing process and so forth, for example, one of the influent flow gas lines can be replaced by a verifying gas line by providing the flow rate measurement unit, the flow rate adjustable valve and the pressure measurement unit thereon. Therefore, the cost of introducing the verifying system can be remarkably reduced since it is not necessary to newly design or install an additional piping. Further, since the volume inside the piping determined by the flow rate adjustable valve, the closing position of each influent flow gas line and the post-confluent valve can be calculated by the reference volume calculation means and the calculated volume can be used as the reference volume, it is not necessary to newly provide a chamber and the like in the gas piping system for obtaining the reference volume as is used in the conventional system. In addition, the accuracy of the flow rate control and the accuracy of the pressure measurement in the verifying gas line can be made reliable, whereby the value of the reference volume can be correctly calculated to be used for verifying a mass flow controller. In other words, since a mass flow controller can be verified while self-verifying the reference volume, the comparing portion can compare the reference parameter determined based on the reliable reference volume to the verifying parameter, so that highly reliable verifying of a mass flow controller can be always performed.

"Furthermore, since the volume inside the piping determined based on the flow rate adjustable valve, the closing position of each influent flow gas line and the post-confluent valve is used as the reference volume, a distance between the target mass flow controller to be verified and the reference volume can be minimized, and therefore a temperature of the gas can be prevented from changing and an influence on the verifying of the mass flow controller can be suppressed. Moreover, since the reference volume is constituted by a gas piping, a surface area to a volume can be increased compared to the case of using a chamber and so forth. Therefore, the temperature exchangeability of a gas can be improved and the measurement environment of a gas temperature and the like can be easily stabilized to be constant in every measurement.

"In addition, since the reference volume is constituted by the gas piping, the reference volume can be made variable by using, e.g., an optional opening/closing valve provided on the post-confluent flow gas line as the post-confluent valve. In more specific, a volume including not only a piping but also a process chamber can be used as the reference volume to be used for verifying a mass flow controller, whereby the reference volume can be freely determined according to an object of verifying.

"Conversely, since the reference volume can be measured based on the time series data of the pressure measurement value, a minimum requirement of the reference volume can be used and the pressure changing amount required for verifying can be produced within a limited time. That is, the verifying can be executed in a short time and such a change in pressure can be easily detected even in the case of verifying a mass flow controller of a small flow rate or even in the case of the flow rate being minutely varied.

"Furthermore, there may be a possible case that one gas line is added to the existing gas piping system to be arranged in parallel to the influent flow gas lines so that the gas flowing therethrough is finally joined to the post-confluent flow gas line and the added gas line is used as the verifying gas line. Even in such a case, the reference volume can be calculated and the mass flow controller can be verified accurately, similarly to the case of providing a verifying gas line by replacement in an existing gas piping system.

"In order to facilitate providing a verifying gas line in an existing gas piping system, it may be possible that the verifying gas line is provided with a differential mass flow controller including the flow rate measurement unit, the flow rate adjustable valve and the pressure measurement unit, and that the pressure measurement unit is used as the flow rate measurement unit.

"For example, when a rate of fall (ROF) type mass flow controller including verifying system is verified, it may be realized by a mass flow controller verifying system for use in a gas piping system provided with one or a plurality of influent flow gas lines each having a mass flow controller and provided with a pre-diverting flow gas line into which gas lines including the influent flow gas lines are joined, wherein the pre-diverting flow gas line is provided with a pre-diverting valve thereon before the diversion of the gas lines. The verifying system comprises: a verifying gas line provided with a flow rate measurement unit adapted to measure a flow rate of a gas, a flow rate adjustable valve by which an opening degree thereof is adjusted so that the measurement flow rate measured by the flow rate measurement unit is coincident with a set flow rate, and a pressure measurement unit adapted to measure a gas pressure, wherein the verifying gas line is arranged in parallel to the influent flow gas lines and connected to the pre-diverting flow gas line; a reference volume calculating portion adapted to calculate a reference volume based on time series data of a measurement pressure measured by the pressure measurement unit, wherein the reference volume is a volume inside a piping portion determined by the flow rate adjustable valve, a closing position of each of the influent gas lines and the pre-diverting valve, in a state that each of the influent gas lines is closed and the pre-diverting valve is closed; a verifying parameter calculating portion adapted to calculate a verifying parameter based on the time series data of the measurement pressure measured by the pressure measurement unit in a state that the influent gas lines, except for an influent gas line having a target mass flow controller to be verified, are closed at the same position as the closing position in the calculation of the reference volume and the flow rate adjustable valve and the pre-diverting valve are closed; and a comparing portion adapted to compare a reference parameter set based on the reference volume and the verifying parameter. Such a verifying system can obtain an effect similar to that in the verifying system as described before.

"As described above, according to the mass flow controller verifying system, verifying method and the program for use therein of the present invention, the verifying gas line can be constituted by providing the flow rate measurement unit, the flow rate adjustable valve and the pressure measurement unit onto one of the plurality of existing influent flow gas lines, whereby it becomes possible to verify a mass flow controller on each of the influent flow gas lines by a simple replacement or an addition of the verifying gas line as mentioned above. In addition, since the reference volume for use in verifying can be calculated from equipment on the influent flow gas lines, there is no need of additionally providing a reference volume. That is, since there is no need of designing or installing a new piping, a chamber, or the like in an existing gas piping system, an introduction cost can be suppressed. Moreover, since the reference volume is formed of the piping, the distance from a target mass flow controller to be verified is close thereto, and therefore a thermal influence on the verifying can be suppressed as small as possible. Furthermore, since the reference volume can be freely set by, for example, closing an optional opening/closing valve prepared in the existing gas piping system, it is also possible to set the reference volume every occasion according to an object, to minimize the volume as necessitated to thereby shorten the verifying time, and to facilitate detection of an abnormality by giving a large readout of a pressure change with a minute flow rate."

For the URL and additional information on this patent, see: Yasuda, Tadahiro; Yamaguchi, Yuji. Mass Flow Controller Verifying System, Verifying Method and Verifying Program. U.S. Patent Number 8646307, filed February 27, 2013, and published online on February 11, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=96&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=4766&f=G&l=50&co1=AND&d=PTXT&s1=20140211.PD.&OS=ISD/20140211&RS=ISD/20140211

Keywords for this news article include: Electronics, Semiconductor, Horiba STEC Co. Ltd..

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Source: Electronics Newsweekly


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