Patent Description:
A flow rate control valve for performing flow rate control of a liquid raw material has been required to be applicable to, for example, atomic layer deposition (ALD) in recent years. In such application, a flow rate is required to be changed at a high speed in a short time by opening/closing a control valve according to a highspeed (having a very short cycle) pulse-shaped control signal. A valve opening/closing driving component applicable to such pulse flow rate control and superior in responsiveness includes a piezoelectric element that expands/contracts simultaneously upon ON/OFF of voltage.

As a flow rate control valve, for a liquid raw material, in which the piezoelectric element is used in a valve drive part thereof, "normally-opened" ones are commonly used. The normally-opened flow rate control valve is configured such that, when voltage applied to a piezoelectric element for driving a valve is zero, the valve is opened so as to allow a liquid raw material to be supplied to a vaporizing chamber provided in the succeeding vaporizer. Therefore, when no voltage is applied due to malfunction of a piezoelectric actuator, power failure, or the like, the liquid raw material is supplied to the vaporizing chamber. When operation is resumed after repair of the piezoelectric actuator or power failure recovery, the liquid raw material having flowed into the vaporizing chamber is gasified and is supplied to a reaction furnace at once, and thus a semiconductor wafer, etc. may be damaged.

Accordingly, a "normally-closed" fluid control valve using a piezoelectric element has been proposed (<CIT>). In the "normally-closed" fluid control valve disclosed in <CIT>, a hollow valve rod is provided in a circular cylindrical member fixed to an upper surface of a valve body, a pressing spring is interposed between a ceiling surface of the circular cylindrical member and an upper end stepped part of the valve rod, and the valve rod is pressed to a valve seat side via a diaphragm provided in the valve body, so that the valve is "closed"; and a piezoelectric element is provided in a space inside the valve rod, an upper surface of the element is abutted on an upper inner surface in the space of the valve rod, a lower surface of the element is fixed to the valve body and is abutted on a bridge that serves as a reference of a change in length of the piezoelectric element, and the valve rod is pressed up by applying voltage to the element, thereby separating the diaphragm from the valve seat, so that the valve is "opened".

<CIT> discloses a piezoelectric linear actuator comprising a laminated piezoelectric actuator having a cylindrical shape; a lower support member supporting the laminated piezoelectric actuator and extending laterally to the left and right of the laminated piezoelectric actuator; a pair of displacement transfer members extending along the left and right sides of the laminated piezoelectric actuator, respectively, to slidably intersect the lower support member and transferring displacement due to the piezoelectric effect of the laminated piezoelectric actuator; and an output part locked to the pair of displacement transfer members below the lower support member and coupling lower end portions of the displacement transfer members, wherein the pair of displacement transfer members are formed to have a width dimension that is the same or substantially the same as the width dimension of the laminated piezoelectric actuator.

In this valve, the diaphragm is driven by ON/OFF of the piezoelectric element, and a "normally-closed state" becomes an "opened state" upon ON and the "opened state" becomes a "closed state" upon OFF as described above. However, a change in length of the piezoelectric element is minute, and thus thermal expansions of the valve rod for transmitting the change in length of the piezoelectric element and the circular cylindrical member including the valve rod therein are extremely important. In <CIT>, the valve rod and the circular cylindrical member are each formed of a general metal member (e.g., stainless steel). Thus, when heat is transferred from the valve body or the surroundings, the length of each of the valve rod and the circular cylindrical member themselves changes, so that the change in length of the piezoelectric element cannot be precisely transmitted to the diaphragm.

In addition, force for pressing the diaphragm to the valve seat by the valve rod influences the closing performance for the valve seat (liquid leakage is caused when the pressing force is weak, and the valve seat is damaged when the pressing force is too strong). Thus, an adjustment function to optimize the pressing spring is also a function indispensable to the normally-closed flow rate control valve, but the valve described in <CIT> Alacks the adjustment function.

The present invention has been made in view of such problems of the above conventional example, and the object of the present invention is to provide a normally-closed flow rate control valve that, firstly, can precisely and quickly transmit a change in length of a piezoelectric element without thermal influence and, secondly, can appropriately adjust a pressing force from a diaphragm to the valve seat.

A flow rate control valve A of a liquid raw material vaporization device according to the present invention comprises the features of claim <NUM>.

According to claim <NUM>, in the flow rate control valve A of the liquid raw material vaporization device described in claim <NUM>,.

According to claim <NUM>, in the flow rate control valve A of the liquid raw material vaporization device described in claim <NUM> or <NUM>,
the valve-actuating part <NUM> includes a plunger <NUM> provided from the support post part <NUM> toward the diaphragm <NUM>, a protective plate <NUM> that is in planar contact with an upper surface of the diaphragm <NUM>, and a steel ball P3 provided between the plunger <NUM> and the protective plate <NUM>.

The present invention is directed to the "normally-closed" flow rate control valve A using the piezoelectric element <NUM> in the above configuration. The support post <NUM> is made of a low thermal expansion member. Therefore, in the normally-closed flow rate control valve A, expansion/contraction of the piezoelectric element <NUM> can be precisely transmitted to the valve-actuating part <NUM> without being affected by a change in the ambient temperature, and valve opening/closing by the diaphragm <NUM> can be precisely performed. Furthermore, at least one of the cooling space R and the cooling fin <NUM> is disposed in the base block upper part 1b, whereby heat on the base block lower part 1a side is prevented from being transferred to the support post part <NUM> side, so that thermal influence on a change Δt itself in length of the piezoelectric element <NUM> on the support post part <NUM> side and transmission of such a change can be prevented.

The elastic member <NUM> is installed between the bearing upper part <NUM> and the lower end support member <NUM>, and the bearing upper part <NUM> is screwed movably forward and backward in the bearing lower part <NUM>, whereby a pressing force F of the elastic member <NUM> during closing of the diaphragm <NUM> can be appropriately adjusted.

With the protective plate <NUM>, the steel ball P3 is prevented from making point contact with the diaphragm <NUM> and is allowed to make surface contact with the diaphragm <NUM>, thereby preventing the steel ball P3 from damaging the diaphragm <NUM>. The steel ball P3 is interposed between the protective plate <NUM> and the plunger <NUM>, whereby the pressing force F from the plunger <NUM> can be perpendicularly applied to the protective plate <NUM>, and eventually to the diaphragm <NUM>, and thus surface contact of the protective plate <NUM> with the diaphragm <NUM> can be perfected.

Hereinafter, the present invention will be described in detail according to illustrated embodiments. A flow rate control valve A of a liquid raw material vaporization device includes a base block <NUM> and a valve opening/closing mechanism <NUM>.

In the present embodiment, the base block <NUM> includes two blocks: a base block lower part 1a and a base block upper part 1b.

The base block lower part 1a includes a first lower part 1a1, and a second lower part 1a2 mounted on the first lower part 1a1.

A valve chamber <NUM> is a space part having a circular shape in a planar view and is provided between the first lower part 1a1 and the second lower part 1a2. The valve chamber <NUM> is divided in a liquid-tight manner into an upper part and a lower part by a diaphragm <NUM> described below, and the lower part on the first lower part 1a1 side is referred to as valve chamber lower part 4a and the upper part on the second lower part 1a2 side is referred to as valve chamber upper part 4b, with the diaphragm <NUM> as the boundary. Since the valve chamber <NUM> is divided in a liquid-tight manner into the upper part and the lower part, a liquid raw material L never leaks from the valve chamber lower part 4a to the valve chamber upper part 4b.

A liquid raw material introduction passage <NUM> through which the liquid raw material L delivered from a storage tank (not shown) passes is formed in the first lower part 1a1, and communicates with a valve seat <NUM> accommodated in a valve seat accommodating hole <NUM>, through the valve seat accommodating hole <NUM> that is formed so as to be recessed in a bottom part of the valve chamber lower part 4a, in the present embodiment. The valve seat accommodating hole <NUM> having a circular shape in a planar view is formed so as to have such a depth as to allow a seat part 3a of the valve seat <NUM> to be fitted therein. A ring-shaped projecting ridge part 4t is protrusively formed around the valve seat accommodating hole <NUM>. A bottom part of the valve seat accommodating hole <NUM> is formed lower by one stage than the ring-shaped projecting ridge part 4t.

A liquid raw material supply path <NUM> for supplying the liquid raw material L, which has flowed into the valve chamber lower part 4a of the valve chamber <NUM>, to a vaporizing chamber <NUM> of a vaporizer (not shown) connected to the flow rate control valve A is provided so as to extend from the bottom part of the valve chamber lower part 4a toward a side face of the first lower part 1a1. In the present embodiment, the liquid raw material introduction passage <NUM> communicates with the valve seat <NUM> through the valve seat accommodating hole <NUM>, and the liquid raw material supply path <NUM> opens to the bottom part of the valve chamber lower part 4a. Although not shown, conversely, a passage opened to the bottom part of the valve chamber lower part 4a may be a liquid raw material introduction passage, and a passage communicating with the valve seat <NUM> may be a liquid raw material supply path and may be connected to the vaporizing chamber.

The valve chamber upper part 4b is provided in the second lower part 1a2. A plunger guide hole <NUM> is drilled in a ceiling part of the valve chamber upper part 4b, and a plunger <NUM> of the valve opening/closing mechanism <NUM> is guided so as to slide upward/downward therein.

The diaphragm <NUM> is formed of a disk-shaped elastic thin plate having a concentrically projecting ridge formed therein, and a center portion thereof is flat-plate-shaped and serves as a valve part 5a that is brought into contact with or separated from the valve seat <NUM>, and an outer circumferential portion thereof is held in a liquid-tight manner between the first lower part 1a1 and the second lower part 1a2. In a state in which no pressing force is applied to the valve part 5a, the valve part 5a at the center of the diaphragm <NUM> is separated from an opening/closing port <NUM> of the valve seat <NUM> with tension of the diaphragm <NUM> as shown in <FIG>, and assembly is performed in this state. As described below, when the valve part 5a is pressed by a valve-actuating part <NUM> that is a part of the valve opening/closing mechanism <NUM>, the valve part 5a is brought into contact with the opening/closing port <NUM> of the valve seat <NUM> to close the opening/closing port <NUM> of the valve seat <NUM> as shown in the <FIG>. As described below, a pressing force F during closing is adjusted according to a deformation amount, based on a length over which a bearing upper part <NUM> is screwed into a bearing lower part <NUM> in the slide bearing part <NUM>, by which an elastic member <NUM> placed at this portion is deformed. The pressing force F from the plunger <NUM> is removed due to an expansion action (voltage application) of a piezoelectric element <NUM>, this separates the valve part 5a at the center of the diaphragm <NUM> from the opening/closing port <NUM> of the valve seat <NUM> due to returning tension of the diaphragm <NUM>, and the valve part 5a is opened, so that the valve seat <NUM> is released from closing.

The base block upper part 1b is mounted on the base block lower part 1a. The base block upper part 1b of the present embodiment is formed from a plurality of post members (here, three post members) installed so as to stand at intervals from each other, and a disk-shaped cooling fin <NUM> is installed at a middle part thereof. A space between the post members is a cooling space R. Cross-sectional areas of the post members are smaller than that of the second lower part 1a2, and thus conduction of heat from the second lower part 1a2 is inhibited here. In addition, heat from the base block lower part 1a side is dissipated and radiant heat from the base block lower part 1a side is inhibited, by the cooling fin <NUM>. Accordingly, in conjunction with the cooling space R, the cooling fin <NUM> inhibits thermal influence from the base block lower part 1a side on the valve opening/closing mechanism <NUM>.

A through-hole <NUM> in which the plunger <NUM>, which is a part of the valve-actuating part <NUM>, is inserted is drilled at the center of the cooling fin <NUM>. An outer diameter of the cooling fin <NUM> is formed to be at least larger than that of the second lower part 1a2 of the base block lower part 1a, so that radiant heat from the base block lower part 1a side to the valve opening/closing mechanism <NUM> is interrupted.

The valve opening/closing mechanism <NUM> includes the slide bearing part <NUM>, a support post part <NUM>, a piezoelectric actuator part <NUM> including the piezoelectric element <NUM>, the valve-actuating part <NUM>, and the elastic member <NUM>. The valve opening/closing mechanism <NUM> has a function for performing precise and quick transmission of expansion/contraction of the piezoelectric element <NUM> to precisely and quickly perform opening/closing of the diaphragm <NUM>. Therefore, the valve opening/closing mechanism <NUM> of the flow rate control valve A of the present invention is structured so as to minimize occurrence of an error due to thermal influence. Specifically, in conjunction with the above-described heat-insulating structure, a support post <NUM> having a low linear expansion coefficient is used, and expansion/contraction of the piezoelectric element <NUM> is directly transmitted to the diaphragm <NUM>, whereby precise and quick valve opening/closing can be performed in the present invention.

The slide bearing part <NUM> includes the bearing upper part <NUM> and the bearing lower part <NUM>.

The bearing lower part <NUM> is a bottomed cylindrical member having an opened upper face, and has a female thread formed on an upper part of the inner circumferential surface, and a through-hole <NUM> drilled at the center of a bottom part. The bearing lower part <NUM> is mounted on the base block upper part 1b.

The bearing upper part <NUM> is a columnar block, an element accommodating hole <NUM> having an opened upper face is drilled at the center of the bearing upper part <NUM>, and a plurality of support post holding holes <NUM> (three support post holding holes in the present embodiment) are provided at the periphery of the element accommodating hole <NUM> so as to penetrate in the up-down direction. In the present embodiment, the support post holding holes <NUM> are formed at equal angular intervals on one circumference, and bearings <NUM> are respectively set therein. The support post <NUM> is inserted in the bearing <NUM>. The bearing upper part <NUM> has a male thread formed on a lower part of an outer circumference and can thus be screwed movably forward and backward in the bearing lower part <NUM>, and an insertion allowance with which the bearing upper part <NUM> is inserted into the bearing lower part <NUM> can be adjusted.

In a bottom part of the element accommodating hole <NUM> of the bearing upper part <NUM>, a steel ball fixing hole <NUM> is drilled, and a second steel ball P2 that makes point contact with a bottom part of the piezoelectric element <NUM> described below and that serves as a measure for expansion/contraction of the piezoelectric element <NUM> is fitted in the steel ball fixing hole <NUM>. On the opposite side (lower surface) of the bottom part of the element accommodating hole <NUM>, a spring upper part holding hole <NUM> is formed so as to be recessed.

The support post part <NUM> includes a plurality of the support posts <NUM> (three support posts <NUM> in the present embodiment), an upper end support member <NUM> mounted to upper parts of the support posts <NUM>, and a lower end support member <NUM> mounted to lower parts of the support posts <NUM>.

Each support post <NUM> is a columnar member in which a metal (e.g., iron-nickel alloy: invar) having a linear expansion coefficient close to zero is used. The support post <NUM> is inserted in the bearing <NUM> of the slide bearing part <NUM> and slides smoothly in the up-down direction.

The upper end support member <NUM> includes a disk-shaped upper end support plate <NUM>, and supplementary posts <NUM> installed so as to be hung from a lower surface of the upper end support plate <NUM> and respectively correspond to the support posts <NUM>, and the upper ends of the support posts <NUM> are screwed to the lower ends of the supplementary posts <NUM>. A female thread hole <NUM> for a fixing screw <NUM> is formed at the center of the upper end support plate <NUM>. The length of each support post <NUM> is much longer than that of the supplementary post <NUM>, and thus thermal expansion of the supplementary post <NUM> in the length direction is negligible (although not shown, the supplementary post <NUM> may be omitted, and the support post <NUM> may be directly screwed to the upper end support plate <NUM>).

Similar to the upper end support plate <NUM>, the lower end support member <NUM> is a disk-shaped member and has mounting holes drilled so as correspond to the support posts <NUM>, and the lower ends of the support posts <NUM> are screwed to the mounting holes, respectively. A protrusion 37t for pressing the plunger <NUM> is protrusively formed at the center of a lower surface of the lower end support member <NUM>. The protrusion 37t is inserted in the through-hole <NUM> of the bearing lower part <NUM>. In addition, a spring lower part holding hole <NUM> is formed so as to be recessed at the center of an upper surface of the lower end support member <NUM> while being aligned with the spring upper part holding hole <NUM> of the bearing upper part <NUM>. The elastic member <NUM> is provided between the spring upper part holding hole <NUM> and the spring lower part holding hole <NUM>, and a screwing allowance with which the bearing upper part <NUM> is screwed into the bearing lower part <NUM> is adjusted such that a predetermined elastic force is produced. As described below, the elastic force is associated with a valve seat closing force (pressing force F) of the diaphragm <NUM> (the spring upper part holding hole <NUM> and the spring lower part holding hole <NUM> are for determining a position of the elastic member <NUM>, but are allowed to be omitted).

The piezoelectric actuator part <NUM> includes the piezoelectric element <NUM>, and a ball guide <NUM> mounted to the upper end of the piezoelectric element <NUM>.

The piezoelectric element <NUM> has a length that rapidly changes according to the magnitude of the applied voltage, an expansion length thereof is zero when the applied voltage is zero, and the higher the applied voltage is, the larger the expansion length is. The length of the piezoelectric element <NUM> is denoted by T when the voltage applied to the piezoelectric element <NUM> is zero, and elongation of the piezoelectric element <NUM> is denoted by Δt when voltage is applied. Here, a reference surface M for measurement of elongation of the piezoelectric element <NUM> is a bottom surface of the piezoelectric element <NUM>.

As described below, the position of the reference surface M of the piezoelectric element <NUM> is adjusted such that, when the expansion length Δt of the piezoelectric element <NUM> is zero (i.e., applied voltage is zero), the diaphragm <NUM> is pressed with an optimal elastic force by the elastic member <NUM>, thereby closing the opening/closing port <NUM> of the valve seat <NUM> with the reliable and appropriate pressing force F.

The piezoelectric element <NUM> has an extremely fast response speed with respect to applied voltage, and even if the voltage applied to the piezoelectric element <NUM> is set so as to have a pulse shape at very short time intervals, the expansion length Δt can be rapidly changed according to the applied voltage.

Between the lower end surface (reference surface M) of the piezoelectric element <NUM> and a bottom surface of the element accommodating hole <NUM> of the bearing upper part <NUM>, the second steel ball P2 for point contact between both the surfaces is provided so as to be fitted in the steel ball fixing hole <NUM>.

The ball guide <NUM> is a columnar member mounted to the upper end of the piezoelectric element <NUM>, and a positioning hole <NUM> in which a first steel ball P1 is to be fitted is drilled at the center of the ball guide <NUM>. The fixing screw <NUM> is screwed in the female thread hole <NUM> at the center of the upper end support plate <NUM>. The first steel ball P1 that is mounted to the lower end of the fixing screw 36to be inserted is located directly above the positioning hole <NUM>, and the fixing screw <NUM> is screwed in the female thread hole <NUM> at the center of the upper end support plate <NUM> with a clearance G larger than the screwed length of the bearing upper part <NUM> described below. The clearance G is expressed by a distance between contact points of the first steel ball P1 and the positioning hole <NUM>. The mounted elastic member <NUM> has a free length, and the length is denoted by S1 (<FIG>).

An initial state of the flow rate control valve A configured as above is a state in which the length of the elastic member <NUM> is the free length S1 as shown in <FIG>, and the elastic member <NUM> is placed, in this state, between the spring upper part holding hole <NUM> of the bearing upper part <NUM> and the spring lower part holding hole <NUM> of the lower end support member <NUM>. At this time point, the bearing upper part <NUM> is screwed in the bearing lower part <NUM> as described above. On the other hand, the diaphragm <NUM> is not deformed and is separated from a seat surface of the valve seat <NUM> with tension thereof, and the opening/closing port <NUM> is in an "opened state".

The valve-actuating part <NUM> is abutted on the diaphragm <NUM> to cause an opening/closing action of the diaphragm <NUM>, and corresponds to the plunger <NUM>, a third steel ball P3, and a protective plate <NUM> in the present embodiment.

The third steel ball P3 is fixed to the lower end of the plunger <NUM> and is abutted on the protective plate <NUM>.

The protective plate <NUM> is a circular metal plate and has a hemispherical recess in which the lower portion of the third steel ball P3 is fitted at the center of an upper surface, and the lower surface of the protective plate <NUM> is flat and located so as to make surface contact with the valve part 5a at the center of the diaphragm <NUM>. The depth of the recess is smaller than a radius of the third steel ball P3, there is a gap between a lower surface of the plunger <NUM> and an upper surface of the protective plate <NUM>, and the pressing force F applied to the plunger <NUM> is perpendicularly applied to the protective plate <NUM> via the third steel ball P3. Since the lower surface of the protective plate <NUM> is flat and makes surface contact with the valve part 5a at the center of the diaphragm <NUM>, the surface pressure is low, and the valve part 5a is protected by the protective plate <NUM> and is not deformed.

The upper end of the plunger <NUM> is abutted on the protrusion 37t of the lower end support member <NUM>, and moves in the up-down direction along up-and-down movement of the protrusion 37t. The plunger <NUM> is inserted in the through-hole <NUM> of the cooling fin <NUM> and the plunger guide hole <NUM> of the second lower part 1a2.

As the elastic member <NUM>, a compression coil spring is used in the present embodiment. Spring members other than the compression coil spring may also be used.

The elastic member <NUM> is deformed from the initial state to obtain an appropriate valve closing force (pressing force F) of the diaphragm <NUM>. Specifically, in the initial state (<FIG>), when the bearing upper part <NUM> is screwed to advance downward in the bearing lower part <NUM>, the lower end support member <NUM> is pressed down via the elastic member <NUM>, so that the protrusion 37t of the lower end support member <NUM> presses the plunger <NUM> down. Since the plunger <NUM> is in contact with the diaphragm <NUM> in an "opened state" via the third steel ball P3 and the protective plate <NUM>, the diaphragm <NUM> is pressed and is deformed toward the valve seat <NUM>.

When screwing of the bearing upper part <NUM> is continued, the diaphragm <NUM> is deformed so as to be eventually brought into contact with the valve seat <NUM>, and the deformation of the diaphragm <NUM> stops in this state. At this time point, since the diaphragm <NUM> is simply in contact with the valve seat <NUM>, liquid leakage is caused when pressure is received from the liquid raw material introduction passage <NUM>. Therefore, in this state, the bearing upper part <NUM> is further continuously screwed. When screwing of the bearing upper part <NUM> is further continued, only the elastic member <NUM> is deformed, to gradually increase the pressing force F for pressing the valve seat 3from the diaphragm <NUM>. Then, when the diaphragm <NUM> is in a closed state with such the pressing force F as to prevent liquid leakage from the valve seat <NUM>, screwing of the bearing upper part <NUM> is stopped, and then fixing is performed with a double nut or the screw part is fixed with an adhesive, for example. Accordingly, the bearing upper part <NUM> and the bearing lower part <NUM> are integrated, and setting of the deformation amount of the elastic member <NUM> ends. The length of the elastic member <NUM> at this time is denoted by S2 (<FIG>).

The first steel ball P1 of the fixing screw <NUM> is spaced apart from the positioning hole <NUM> of the ball guide 41while sufficiently maintaining the clearance G during screwing of the bearing upper part <NUM> in the bearing lower part <NUM>, and thus is not in contact with the positioning hole <NUM> even after the setting of the deformation amount of the elastic member <NUM> ends.

After the setting of the deformation amount ends, fastening is performed until the first steel ball P1 of the fixing screw <NUM> is bought into contact with the ball guide <NUM>. At this time, excessive fastening changes the deformation amount of the elastic member <NUM> and causes liquid leakage, and thus the fastening amount is such an amount as to simply bring the first steel ball P1 into contact with the ball guide <NUM>.

Accordingly, the flow rate control valve A functions as a "normally-closed" flow rate control valve. Specifically, the diaphragm <NUM> is deformed with the elastic force (pressing force F) of the elastic member <NUM>, so that the valve seat <NUM> is normally closed.

Next, an action of the flow rate control valve A of the present invention will be described. The flow rate control valve A is incorporated into a publicly known semiconductor manufacturing system and used, for example. The flow rate control valve A is connected to a storage tank (not shown) and receives supply of the liquid raw material L from the storage tank. The supplied liquid raw material L is delivered to the valve seat <NUM> through the liquid raw material introduction passage <NUM>.

In a "normally-closed state" in <FIG>, the valve seat <NUM> is closed by the diaphragm <NUM> and stopped at the opening/closing port <NUM>. When an operation of vaporizing the liquid raw material L starts, voltage is applied to the piezoelectric element <NUM>. The piezoelectric element <NUM> rapidly elongates upward with respect to the reference surface M according to the applied voltage, and the upper end support plate <NUM> is pressed up via the fixing screw <NUM> by the elongation amount. Such elongation is denoted by Δt. Accordingly, the support posts <NUM>, and the lower end support member <NUM> provided to the lower end of the support posts <NUM> are rapidly moved upward by the amount (elongation Δt), and the elastic member <NUM> is compressed (by elongation Δt) by being pressed by the bearing upper part <NUM> fixed to the bearing lower part <NUM> as above. The length of the compressed elastic member <NUM> is denoted by S3 (<FIG>).

When the protrusion 37t of the lower end support member <NUM> pressing the plunger <NUM> is moved upward according to the expansion of the piezoelectric element <NUM>, the diaphragm <NUM> is deformed in a returning direction according to the upward movement, and the plunger <NUM> is pressed up and the opening/closing port <NUM> of the valve seat <NUM> is opened. At this time, a lower end of the elastic member <NUM> is held by the lower end support member <NUM>, and thus the elastic force thereof is applied to the elongated piezoelectric element <NUM> via the support posts <NUM> but not applied to the diaphragm <NUM>. Therefore, the diaphragm <NUM> is returned with its own tension in the returning direction and is separated from the valve seat <NUM>. Thus, the separation width is equivalent to the above Δt. Subsequently, the liquid raw material L flows into the valve chamber lower part 4a through the opened opening/closing port <NUM>, and flows into the vaporizing chamber <NUM> of the vaporizer through the liquid raw material supply path <NUM> that is open to a bottom part of the valve chamber lower part 4a.

To cause the valve seat <NUM> in this state to be in a "closed state", the applied voltage to the piezoelectric element <NUM> is caused to be zero. When the applied voltage becomes zero, the length of the piezoelectric element <NUM> rapidly returns to an original length T. The lower end support member <NUM> of the support post part <NUM> is lowered according to the contraction, and presses the diaphragm <NUM> down via the plunger <NUM>. The diaphragm <NUM> is pressed down with the pressing force F of the elastic member <NUM>, to close the valve seat <NUM> as above. Accordingly, the liquid raw material L is delivered precisely at an indicated flow rate to the vaporizing chamber <NUM> without any time lag.

In the above-described valve opening/closing operation, in the flow rate control valve A of the present invention, the base block lower part 1a and the valve opening/closing mechanism <NUM> are divided by the base block upper part 1b, and the cooling space R and the cooling fin <NUM> are provided in the base block upper part 1b. Thus, heat transferred from the base block lower part 1a side is dissipated by the cooling fin <NUM>, and, at the same time, the base block upper part 1b is cooled with air in the cooling space R, and thus the valve opening/closing mechanism <NUM> receives no thermal influence from the base block lower part 1a provided with the valve chamber <NUM>. In addition, the base block upper part 1b is formed from the plurality of post members each having a narrow cross section, whereby heat conduction from the base block lower part 1a is inhibited.

The linear expansion coefficient of the piezoelectric element <NUM> is close to zero on the valve opening/closing mechanism <NUM> side, and is nearly equal to the linear expansion coefficient of an alloy used in the support posts <NUM>, whereby the dimensional change Δt of the piezoelectric element <NUM> is precisely and rapidly transmitted to the diaphragm <NUM>.

Claim 1:
A normally-closed flow rate control valve (A), comprising:
a base block (<NUM>) provided with a valve chamber (<NUM>) in which a valve seat (<NUM>) through which a liquid raw material (L) flows, and a diaphragm (<NUM>) that is brought into contact with or separated from the valve seat (<NUM>) so as to close/open the valve seat (<NUM>) are installed; and
a valve opening/closing mechanism (<NUM>) that performs opening/closing drive of the diaphragm (<NUM>), wherein
the valve opening/closing mechanism (<NUM>) includes:
a slide bearing part (<NUM>) installed on the base block (<NUM>) and provided with a bearing (<NUM>);
a support post part (<NUM>) including a support post (<NUM>) that is inserted slidably in the bearing (<NUM>) and that moves upward and downward in a diaphragm direction;
a piezoelectric actuator part (<NUM>) provided between the slide bearing part (<NUM>) and the support post part (<NUM>), the piezoelectric actuator part (<NUM>) including a piezoelectric element (<NUM>) that expands by application of voltage, and presses up the support post part (<NUM>) in such a direction as to separate the support post part (<NUM>) from the diaphragm (<NUM>) with respect to the slide bearing part (<NUM>) as a reference; and
a valve-actuating part (<NUM>) that is provided from the support post part (<NUM>) toward the diaphragm (<NUM>) and that performs opening/closing drive of the diaphragm (<NUM>) along up-and-down movement of the support post part (<NUM>),
the support post (<NUM>) of the support post part (<NUM>) is made of a low thermal expansion member,
the slide bearing part (<NUM>) includes a bearing lower part (<NUM>) that is bottomed and that has an opened upper face,
the support post part (<NUM>) includes the support post (<NUM>), an upper end support member (<NUM>) that is provided on an upper end of the support post (<NUM>) and on which an upper end of the piezoelectric actuator part (<NUM>) is abutted, and a lower end support member (<NUM>) provided between the bearing upper part (<NUM>) and the bearing lower part (<NUM>), and
an elastic member (<NUM>) is installed between the bearing upper part (<NUM>) and the lower end support member (<NUM>),
characterized in that
the slide bearing part (<NUM>) further includes a bearing upper part (<NUM>) that is screwed movably forward and backward in the bearing lower part (<NUM>) and that is provided with the bearing (<NUM>) in which the support post (<NUM>) is inserted.