JP3270192B2 - Flow sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow sensor which can be suitably used for a gas supply system in a semiconductor manufacturing line or general industry.

[0002]

2. Description of the Related Art Various gases are used to manufacture semiconductors. For example, in a process of forming an oxide film such as SiO _{2 on} the surface of a substrate, monosilane (Si) is used.
A flammable gas such as H ₄ ) and hydrogen (H ₂ ) and a flammable gas such as nitrous oxide (N ₂ O) and oxygen (O ₂ ) are simultaneously flowed into the process chamber to cause a predetermined reaction. In this case, a check valve (check valve) is used to prevent the combustion supporting gas (for example, N ₂ O) from flowing back to the cylinder side of the heating gas (for example, SiH ₄ ).

[0003]

However, the non-return valves which have been commercially available in the past are so-called mechanical valves which open and close the valve element according to the relationship between the strength of the spring and the pressure. It is difficult to completely eliminate it, and there are defects such as particles in the fluid clogging the check valve and a large amount of gas may flow back when a slight gap is created, and an abnormality has occurred Sometimes an electrical signal is not output to notify the occurrence of an abnormality, and therefore, the abnormal state continues, causing an extremely dangerous situation, and in the forward direction, a fixed amount of gas flows due to the pressure difference generated on both sides of the valve Due to the structure, there is a disadvantage that the flow rate exceeds a predetermined flow rate, that is, the flow rate cannot be limited when an overflow occurs.

That is, the conventional check valve may not be able to completely prevent the backflow, and it is not possible to grasp the amount of the backflow of the fluid.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object of the present invention is to provide a useful flow sensor capable of solving the problems of a currently available check valve. It is in.

[0006]

In order to achieve the above-mentioned object, a flow sensor according to the present invention comprises a bypass portion for bypassing a fluid between a fluid inlet and a fluid outlet formed in a main body block; A flow measurement unit for measuring the flow rate is provided in parallel, and a backflow detection unit is provided between the flow measurement unit and the fluid outlet to detect a minute fluid in a reverse direction from the fluid outlet toward the fluid inlet. It is characterized by.

In this case, the output of the flow measuring unit may be output as a positive flow output signal, and the output of the reverse direction may be output as a negative flow output signal. Also,
The configuration may be such that the output of the backflow detection unit is compensated when an excessive flow rate significantly larger than the set value flows in the reverse direction. Then, an alarm may be issued when a flow rate larger than the set value flows. Further, an alarm signal may be output when the alarm state continues for a certain period of time or more, a display device for displaying the alarm state may be provided in the main body block, or the alarm detection level may be variable.

[0008]

In the flow sensor having the above-described structure, it is possible to detect the flow rate in the forward direction, as well as to reliably detect the occurrence of the overflow and the reverse flow in the forward direction.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

First, FIG. 2 is a longitudinal sectional view showing an example of a flow sensor A according to the present invention. In this figure, reference numeral 1 denotes a main body block having a fluid inlet 2 formed at one end and a fluid inlet 2 at the other end. A fluid outlet is formed, and a fluid flow path 4 is formed in the inside so as to connect the fluid inlet 2 and the fluid outlet 3. A bypass element 5 having a constant flow rate characteristic is provided in the fluid flow path 4 near the fluid inlet 2 side, and a bypass portion 6 is formed. Reference numerals 7 and 8 denote connection members having a fluid flow path formed therein.

Reference numeral 9 denotes a flow rate measuring section provided in parallel with the bypass section 6, for measuring the flow rate of the fluid flowing from the fluid inlet 2 to the fluid outlet 3 (hereinafter referred to as the forward direction). That is, reference numeral 10 denotes a flow measurement block provided on the upper part of the main body block 1, and a thin tube 11 as an inverted U-shaped measurement flow passage is held in the flow measurement block 10 so as to be parallel to the bypass section 6. Two sensor coils 12, 12 are wound around a flat horizontal portion of the thin tube 11. Two sensor coils 12, 12
Are connected to a bridge circuit (not shown). The flow rate measuring unit 9 is configured to measure a relatively large flow rate flowing in the reverse direction (for example, a full scale value is 100 ml / min or more, and in some cases, 1000 ml / min). 13 is a thin tube 11 and a sensor coil 12,
12 is a cover body that covers 12. The configuration so far is
There is no difference from the conventional mass flow meter.

Numeral 14 denotes a backflow detecting unit interposed in the fluid flow path 4 between the flow rate measuring unit 9 and the fluid outlet 3, and a minute flow heading from the fluid outlet 3 toward the fluid inlet 2 (hereinafter referred to as a reverse direction). (For example, 5 cc / min or less) is provided for detecting a fluid. That is, in this embodiment, a backflow detection block 15 is provided above the main body block 1, and the backflow detection block 15 holds an inverted U-shaped thin tube 16 having an inner diameter larger than that of the thin tube 11. Two sensor coils 17, 1 on a flat horizontal part
7 is wound. The two sensor coils 17, 17 are connected to a bridge circuit (not shown) (not shown). Reference numeral 18 denotes a cover body that covers the thin tube 16 and the sensor coils 17.

When gas flows in the forward or reverse direction through the flow sensor A having the above-described configuration, the flow rate is detected by the flow rate measuring section 9 and the reverse flow detecting section 14, and a signal is output. A processing circuit as shown in FIG. 1 is configured to perform flow rate display and processing of an output when an overflow occurs in the forward direction or a flow in the reverse direction, that is, when a reverse flow occurs.

That is, in FIG. 1, reference numerals 21 and 22 denote mass flow meter sections (hereinafter referred to as forward MFM 21 and mass flow meter sections) which perform calculations based on the detection outputs of the flow rate measuring section 9 and the backflow detecting section 14.
In the reverse direction MFM22), the AC flow signals a and b as shown in FIG. 23 is forward MF
This is an inverted output circuit configured to invert only the hatched positive signal of the flow signal a output from M21 and not output the negative signal. Reference numeral 24 denotes an inverted output circuit configured to invert only the hatched positive signal of the flow signal b output from the reverse MFM 22 and not output the negative signal. An output circuit 25 calculates the difference between the amplified output signals a and b, and outputs a subtraction output c (= ab).

The output 23a of the forward MFM 21 or the output b of the backward MFM 22 is performed by the circuits 23 to 25.

In the flow rate measuring section 9 and the backflow detecting section 14, when a fluid exceeding the flow rate measuring range flows, its output signal becomes saturated in proportion to the flow rate. When the flow rate is further increased, the output signal becomes smaller on the contrary. In particular, since the backflow detecting section 14 is not provided with a via pass section, the above-mentioned properties may cause a problem.

Reference numeral 26 denotes a compensation circuit provided to solve the above-mentioned problem. When the absolute value of the output a of the backward MFM 21 becomes larger than a certain level, the backward MFM 22
The correction signal d is applied to the inverted output circuit 24 instead of the output b.

[0018] 27 in the vortex determination warning unit for outputting a predetermined alarm signal ALK when the flow rate of the fluid flowing through the flow sensor A in the opposite direction becomes excessive (e.g. on a certain set Ne以), reverse MFM21 It compares the comparison voltage RefV ₂ as a setting value and the output a, and is configured to allow an alarm display by alarm or LED, such as a buzzer.

Reference numeral 28 denotes a reverse flow discriminating / warning unit which outputs a predetermined alarm signal ALG when the fluid flows in the flow sensor A in the reverse direction and the reverse flow continues for a predetermined time or more. The output b of the reverse MFM 22 and the set value are output. Comparison voltage RefV as
_3. A variable time setting means 31 provided with a delay circuit 30 and a comparison circuit 29 for comparing
Thus, when a backflow of, for example, about 1 cc / min continues for 5 seconds, an alarm such as a buzzer or an alarm display by an LED can be performed.

A device for displaying an alarm state such as a buzzer or an LED is provided at an appropriate position of the main body block 1. Further, the comparison voltages RefV ₂ , Re
Since fV ₃ is variable, the alarm detection level can be set as appropriate.

32 and 33 are, for example, 2% of the full scale value.
In comparison circuit for omitting Show (2% FS) following flow, the output a reverse MFM21, output b and the comparison voltage RefV ₄ as 2% FS reverse MFM22 is in each of the circuits 32 and 33 So that they can be compared. With this configuration, it is possible to eliminate the influence of errors due to aging or noise.

FIG. 3 shows a flow rate-output voltage characteristic in the flow rate sensor A described above.

In the flow sensor A having the above configuration, when the fluid is flowing in the reverse direction, the flow rate is displayed based on the detection output of the flow rate measuring section 9. When the flow rate in the reverse direction exceeds the set value, an alarm is immediately issued or a warning is displayed. Further, in the case where the fluid flows in the reverse direction, a predetermined warning is issued or a warning is displayed when the backflow continues for a predetermined time.

Depending on the type of the fluid to be measured or its flow rate, a bypass similar to the bypass section 6 may be provided in parallel with the thin tube 16, and in this case, the thin tube 16 has a small inner diameter. Can be used.

Next, an example of use of the flow sensor A having the above configuration will be described. First, FIG. 4A shows that a backflow detection sensor G composed of only the backflow detection section of the flow sensor A is incorporated in a special gas line. This shows an example.
Reference numeral 1 denotes a cylinder containing, for example, SiH ₄ , reference numeral 42 denotes a regulator, reference numeral 43 denotes a semiconductor manufacturing apparatus, and a backflow detection sensor G is interposed in a special gas line 44 connecting the cylinder 41 and the semiconductor manufacturing apparatus 43. According to this configuration, it is possible to detect whether or not backflow has occurred.

FIG. 3B shows the backflow detecting sensor G.
In this figure, a special gas line N ₂ purge line is shown. In this figure, reference numerals 51 and 52 denote flammable gases (for example, S
iH ₄ ), a special gas line for supplying a combustible gas (for example, N ₂ O), and a mass flow controller 54 for controlling the flow rate, an open / close valve 55, and the like are interposed in each of them. Reference numerals 56 and 57 denote N ₂ purge lines, each line 5
The backflow detection sensor G is interposed with the open / close valve 58 at 6, 57. According to this configuration, for example, the SiH ₄ flowing in the flammable gas line 51 flows in the reverse direction through the on-off valve 58, and the SiH ₄ flows in the direction of arrow X and flows in the direction of the flammable gas line 57. Even if there is, the backflow is detected by the backflow detection sensor G, and a disaster such as an explosion can be prevented.

[0027]

As described above, according to the present invention,
It allows the flow rate detection in the forward direction, of course, possible to reliably detect that it and backflow vortex is generated occurs in the forward direction. Therefore, for example, it is possible to detect whether a necessary gas is excessively supplied in a semiconductor manufacturing line. Further, it is possible to prevent the flammable gas flowing in the flammable gas line from flowing into the flammable gas line side by flowing back through the check valve.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an example of a signal processing circuit of the flow sensor.

FIG. 2 is a longitudinal sectional view showing an example of the structure of the flow sensor according to the present invention.

FIG. 3 is a diagram showing the flow rate-output voltage characteristics.

FIGS. 4A and 4B are diagrams showing examples of use of the flow sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Body block, 2 ... Fluid inlet, 3 ... Fluid outlet, 6 ...
Bypass section, 9: flow rate measuring section, 14: backflow detecting section.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kozo Shimomura 2 Higashi-cho, Kichijoin-gu, Minami-ku, Kyoto, Kyoto Examiner, ESTEC Co., Ltd. Masayuki Mori (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 1 /-15 /

Claims (7)

(57) [Claims] A bypass unit configured to bypass a fluid between a fluid inlet and a fluid outlet formed in the main body block;
A flow measurement unit that measures the flow rate of the fluid is provided in parallel, and a backflow detection unit that detects a minute fluid in the opposite direction from the fluid outlet to the fluid inlet direction is provided between the flow measurement unit and the fluid outlet. A flow sensor characterized by the following. 2. The flow sensor according to claim 1, wherein an output of the flow measurement unit is output as a positive flow output signal, and an output in the reverse direction is output as a negative flow output signal. 3. The flow sensor according to claim 1, wherein an output of the backflow detection unit is compensated when an excessively large flow in the reverse direction is larger than the set value. 4. The flow sensor according to claim 1, wherein an alarm is issued when a flow rate larger than a set value flows. 5. The flow sensor according to claim 4, wherein an alarm signal is output when the alarm state continues for a predetermined time or more. 6. The flow sensor according to claim 4, wherein a display device for displaying an alarm state is provided in the main body block. 7. The flow sensor according to claim 4, wherein the alarm detection level is variable.