JP3535566B2 - Method and apparatus for producing mixed gas of predetermined concentration - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for mixing two or more gases to a predetermined concentration. BACKGROUND OF THE INVENTION In the semiconductor industry, SiH ₄ , PH ₃
And other special material gases are used. These SiH
₄ , PH ₃ gas is usually used after being diluted with a balance gas such as H ₂ , N ₂ , He, Ar and filled in a cylinder container. In this case, in order to keep the supply quality of the obtained semiconductor constant without changing the conditions of the manufacturing process, the fluctuation of the mixing ratio of the two gases at a predetermined concentration must be suppressed to zero or a minimum allowable range. . For example, H
When an attempt is made to obtain a mixed gas containing PH ₃ 1 parts by volume with respect to ₂ 10 parts by volume, always PH _3: H ₂ is 10: 1 is that it must be mixed with (volume basis). Conventionally, for example, a dopant such as PH ₃ and H ₂
And the like were mixed in an apparatus as shown in FIG. However, in the conventional method, a mixed gas of a dopant gas and a diluent gas having a constant concentration cannot always be obtained. For example, even if an attempt is made to obtain a mixture of 1 liter of dopant gas with respect to 10 liter of dilution gas, a mixture having a volume ratio of 10: 1 is not always obtained. Conventionally, semiconductors have been manufactured using cylinders previously filled with a gas mixture having a predetermined ratio. However, in this case, in order to obtain a mixed gas of the dopant gas and the diluent gas at various ratios, a plurality of mixed gas cylinders must be prepared. In addition, conversion of cylinders must be performed relatively frequently in order to use the mixed gas. In addition, every time the cylinder container is replaced, the mixed gas concentration fluctuates within a range of ± 5% in relative concentration. Was. SUMMARY OF THE INVENTION The present invention is directed to an apparatus and method for mixing two or more gases at a predetermined rate from a single filled cylinder. According to the present invention, in a method of mixing a second fluid with a first fluid at a predetermined ratio, a gas flow rate of the first fluid is measured, and a correlation based on the measured flow rate of the first fluid is used for correlation of concentration correction. The relational expression y = ax ^b + c (where x ｛l / min] is the measured flow rate of the first fluid, y ｛l / min] is the set flow rate of the second fluid, and a, b, and c are the second fluid versus the first fluid. The value varies based on the ratio of the fluids, but at a constant concentration ratio of the two fluids, it is an experimentally determined constant) and the value calculated based on the gas flow rate of the second fluid is controlled in real time. A first fluid and a second fluid.
The present invention relates to a method for mixing fluids at a predetermined ratio. An apparatus for implementing a method of mixing a second fluid with a first fluid at a predetermined ratio comprises a first fluid through which a first fluid flows.
A flow path, a second flow path through which the second fluid flows, a means for measuring a gas flow rate of the first fluid, a means for generating a signal based on the measured flow rate of the first fluid, and a gas for the second fluid based on a signal from the means. The control means includes means for setting a flow rate and controlling the flow rate in real time, and the control means adjusts the set flow rate of the second fluid to a concentration correction correlation expression y = ax ^b + c (where x ｛l / min) The measured flow rate of one fluid, y ｛l / min] is the set flow rate of the second fluid, and a, b, and c are the second fluid versus the first fluid
It varies depending on the ratio of the fluids, but at a constant concentration ratio of the two fluids, it is an experimentally determined constant). The present invention will be described with reference to the drawings. In FIG. 2, a diluent gas such as H ₂ , He or the like flows from the first flow path, a dopant gas such as SiH ₄ or PH ₃ flows from the second flow path, and y = ax ^b + c (expression) according to the output voltage from the MFM. Where x is the flow rate of the first fluid, y is the flow rate of the second fluid, a
And b and c vary with the ratio of the second fluid to the first fluid, but are constants determined experimentally at a constant ratio of the two fluids) to control the flow rate of the dopant gas in real time. For example, when trying to obtain a mixture in which the diluent gas is H ₂ , the dopant gas is PH ₃ , and the dope gas concentration is 10%, for example, a =
0.992 and b = 0.959. When the concentration becomes 20%, for example, a = 0.823, b = 0.854, c = 0
It becomes. Since this data changes little by little over time, it is preferable to perform a zero check every 1-2 hours. Zero check means that the supply of gas is stopped and a signal from a means for generating a signal based on the flow rate of the first fluid is used.
The above a and / or b and / or c are corrected. FIG. 2 will be described in more detail. 1
Is a first flow path for a dilution gas, and 2 is a second flow path for a dopant gas.
Flow path, 3 is valve, 4 is filter, 5 is valve, 6 is MFM
(Mass flow meter), 7 is a valve, 8 is a valve, 9 is a filter, 10 is a valve, 11 is a mass flow controller, 12 is a valve, 13 is a valve for purge gas, 14 is a pressure gauge for measuring internal pressure, and 15 is a buffer tank. , 16 are electronic pressure regulators for adjusting the pressure of the mixed gas. The dilution gas passes through the valve 3, the filter 4, and the valve 5, and the flow rate is measured by the MFM 7. On the other hand, the flow rate of the dopant gas is controlled by the MFC 11 through the valve 8, the filter 9, and the valve 10. The diluent gas and the dopant gas pass through the valves 11 and 12, respectively, and are mixed and agitated at a junction in the valves, and are introduced into the buffer tank.
In this case, the flow rate of the dilution gas line in the MFM 12 is input to the arithmetic circuit as an output voltage, and in the MFC of the dopant gas line, a voltage corresponding to the flow rate to be added is calculated and input to the MFC. According to this control method, it becomes possible to constantly generate a mixed gas having a constant concentration following the demand flow rate at the use point (semiconductor manufacturing apparatus side). The pressure of the mixed gas from the buffer tank 15 is adjusted by an electronic pressure regulator 16 and is sent to a use point through a valve 17. When the apparatus is stopped, a purge gas is introduced to drive out the dopant gas remaining in the system. The present invention also includes an embodiment in which one gas is mixed with two or more gases. This is the mode shown in FIG. The device shown in FIG.
, Gas B and gas C are uniformly mixed. In this case, the relationship between the gas A and the gas B is expressed by the formula y = ax ^b + c (where x is the flow rate of the gas A, y is the flow rate of the gas B, and a, b, and c vary depending on the ratio of the gas B and the gas A). Yes, but 2
For a given ratio of two fluids, this is an experimentally determined constant). The gas A and the relationship between the gas C is the formula ^{y '= a'x b' + c'───} (x in the formula, the flow rate of the gas A, y 'is the flow rate of the gas C, a'
And b 'and c' vary with the ratio of gas C to gas A, but for a constant ratio of the two fluids, are empirically determined constants). Regardless of the type of gas to be mixed with the first fluid (gas A), the same system as the gas C shown in FIG. In FIG. 3, 2
Reference numeral 8 denotes a valve, 29 denotes a filter, 30 denotes a valve, 31 denotes an MFC for gas C, 27 denotes a valve, and 33 denotes a purge gas valve for gas C. The apparatus shown in FIG. 2 uses a dopant gas (S
Although examples of iH ₄ ) and the diluent gas (He) are shown, the type of gas is not limited in the present invention. When the use at the use point is stopped, the internal pressure of the pipe reaches the upper limit, or the flow rate of the first flow path reaches the lower limit, at which time the supply of both gases is stopped. When the use point starts to be used, the internal pressure of the pipe reaches the lower limit, at which time the supply of both gases is started. By connecting a reference concentration analyzer every certain period (for example, once a year), the output values of the two flow controllers are read, and the above a, b and c are corrected. An embodiment of the present invention will be described below. However, this is only an example of the content of the invention, and the present invention is not limited to this content. Embodiment 1 This embodiment is based on a flow rate proportional control method (a method of controlling the flow rate of the component gas MFC so that the concentration thereof is constant with respect to the dilution gas MFM flow rate) in a mixing apparatus. This is an example of clarifying the correlation between the flow rate and the set value of the MFC, and confirming that the generated concentration becomes constant when the proportional control is performed using the relational expression. He as a diluent gas and Si as a component gas
Using H ₄ , adjust the supply pressure of He gas to the regulator RV
-2 to 3.5 kg / cm ² G, and the supply pressure of the SiH ₄ gas to 4 kg / cm ² G by RV-1. FIG. 4 shows the system flow. An ultrasonic transmission type mixed gas concentration meter was used as the analyzer. In addition, the analyzer always has 500c by MFC-2.
It was adjusted so that a mixed gas having a flow rate of c / min was sampled. The mixed gas generation flow rate is set to 0 by MFC-3.
Adjustment was performed at a pitch of 500 cc / min in the range of 7 l / min. The flow rate of addition of SiH ₄ gas was adjusted by MFC-1 so that a predetermined generation concentration (20%) was obtained for each mixed gas generation flow rate. The He gas flow reading (X) and the SiH ₄ gas flow setting (Y) when the generated concentration matched the predetermined generated concentration were regressed by the least square method. The regression method was a regression using a power number (Y = ax ^b + c). As a result of the regression, a correlation of Y = 0.982x ^-0.968 was obtained. The generated concentration was compared between the method of performing proportional control using the correlation equation obtained by the above method and the conventional method of proportional control according to the set value of the flow rate. The flow rate is set to 0 to 7 by the MFC-3 on the subsequent stage.
Generated concentration when changed to 1 / min (see Fig. 5)
It was confirmed that in the proportional control using the correlation equation, it was always constant with the change in the flow rate. When the concentrations were 10%, 30%, and 40%, the generated concentration was confirmed using the same method. FIG. 6 shows the relationship between the flow rate and the generated concentration at each concentration. Embodiment 2 FIG. 7 shows a flow of a mixing apparatus for automatic operation. The automatic operation means that when the use of the mixed gas is stopped at the use point, the flow rate indicated by the MFM is 3
When the pressure falls below 00 cc / min, the pneumatic valve AV-3,
4, 5, and 6 are closed, and the supply of the mixed gas is stopped. When the mixed gas is started to be used at the point of use, the pressure sensor (P) detects that the pressure in the pipe has decreased, and when the indicated value becomes an indicated value of 3.3 kg / cm ² G or less. The pneumatic valves AV-3, 4, 5, 6 are opened to start supply. The supply pressure of the mixed gas was set to 3 kg / cm ² G by an auto pressure regulator (UR), and the generated concentration set value was set to 20%. [0027] He is used as the diluent gas and the supply pressure is set to 3.
It was adjusted to 5kg / cm ² G, to adjust the supply pressure using SiH ₄ as a component gas to 4.0kg / cm ² G. An MFC is installed at the outlet of the device to simulate the flow rate fluctuation at the use point, and the mixed gas generation flow rate of the mixing device is 7 → 5 → 3 → 1 → 0.5 → 0 → 0.5
→ 1 → 3 → 5 → 7 l / min. It was confirmed that the generated concentration was constant regardless of the change in the flow rate. (See FIG. 8). Embodiment 3 The zero point output (output voltage in the absence of gas flow) of the MFM and the MFC when the correlation is obtained in the embodiment 1 is set to 0 mV. The output at the zero point at this time is set as a reference voltage,
This voltage value changes over time, the arithmetic expression of the correlation equation Y = ax ^b of Tokimoto the output voltage of MFM In the absence of flow of the gas output voltage of emV and MFC became DMV Y −d = a (x−e) Rewrite to ^b and use a new arithmetic expression to calibrate the zero point. Y = ax ^b + c → Y = ax ^b + c ′ A change with time in the generated concentration was confirmed using the conventional method and the control by the above-described method. As a method of confirmation, He was used as a diluent gas and SiH ₄ was used as a component gas, the generation concentration was set to 20%, and the generation flow rate was adjusted to 3 l / min. When the generated concentration was checked every two months for 12 months, if the calibration of the zero point was not performed, a deviation of 1.2% was generated even if the generated concentration was set to 20%. did. However, in the control method by rewriting the arithmetic expression in which the zero point was calibrated with the change of the zero point, no change was observed in the generated concentration during this period. (See Fig. 9)
Embodiments of the present invention are as follows. 1. An apparatus that mixes a second fluid with a first fluid at a predetermined ratio, and detects a first flow path through which the first fluid flows, a second flow path through which the second fluid flows, and a gas flow rate of the first fluid. Means for generating a signal based on the flow rate of the first fluid, and control means for controlling the gas flow rate of the second fluid in real time by a signal from the means, wherein the flow rate of the second fluid is y = ax
^b + c (where x is the flow rate of the first fluid, y is the flow rate of the second fluid, a and b and c vary with the ratio of the second fluid to the first fluid, but at a constant ratio of the two fluids Is
An apparatus that mixes two fluids controlled in accordance with a predetermined ratio according to an experimentally determined constant. 2. When the pipe internal pressure reaches the upper limit, or when the flow rate of the first flow path reaches the lower limit, supply of both gases is stopped, and when the pipe internal pressure reaches the lower limit, supply of both gases is started. 1 above
The described device. 3. When the gas supply is stopped, the signal from the means for generating a signal based on the flow rate of the first fluid,
The apparatus according to the above item 1, wherein the correction of a and / or b and / or c is performed. 4. The apparatus according to the above item 1, wherein the output values of the two flow control devices are read by connecting a reference concentration analyzer every certain period, and the values a and / or b and / or c are corrected. 5. In a method of mixing a second fluid with a first fluid at a predetermined ratio,
The gas flow rate of the fluid is detected, and a signal based on the flow rate of the first fluid is used to calculate the equation y = ax ^b + c (where x is the flow rate of the first fluid, y is the flow rate of the second fluid, and a and b and c are It varies with the ratio of the two fluids to the first fluid, but at a constant ratio of the two fluids, it is an experimentally determined constant. Mixing the first fluid and the second fluid at a predetermined ratio. 6. In a method of mixing two or more types of second fluids at a predetermined ratio with respect to a first fluid, a gas flow rate of the first fluid is detected, a signal based on the flow rate of the first fluid, and a flow rate of the second fluid are controlled. And for each of the second fluids, the equation y = ax ^b +
c, y '= a'xb' + ^c '{where x is the flow rate of the first fluid, y, y'} is the flow rate of each of the second fluids, a, a 'and b, b And {circumflex over (c)} vary depending on the ratio of each of the second fluid to the first fluid, but for a constant ratio of the two fluids, is an empirically determined constant). A method of mixing a first fluid and a second fluid at a predetermined ratio, wherein a gas flow rate of each of the two fluids is controlled in real time.
7. An apparatus for mixing two or more second fluids at a predetermined ratio with respect to a first fluid, a first flow path through which the first fluid flows, a second flow path through which each of the plurality of second fluids flows, A second fluid including a means for detecting a gas flow rate of one fluid, a means for generating a signal based on the flow rate of the first fluid, and a control means for controlling a gas flow rate of each of the plurality of second fluids in real time by a signal from the means each flow rate ^{y = ax b + c, y} '= a'x b' + c'─
{(Where x is the flow rate of the first fluid, y, y ′} is the flow rate of each of the second fluids, a, a ′} and b, b ′} and c, c ′} are the second. The ratio varies depending on the ratio of each fluid to the first fluid, but at a fixed ratio of the two fluids, it is a constant determined experimentally). Mixing equipment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a conventional two-gas mixing apparatus. FIG. 2 is a schematic diagram of a mixing device of the present invention. FIG. 3 is a schematic view of a mixing apparatus according to another embodiment of the present invention. FIG. 4 is a schematic diagram of a system flow for implementing the first embodiment. FIG. 5 is a graph showing a relationship between a flow rate and a generated concentration. FIG. 6 is a graph showing the relationship between the flow rate and the generated concentration at various concentrations. FIG. 7 is a schematic view of an apparatus for automatic driving according to the present invention. FIG. 8 is a graph showing the relationship between time, flow rate, and generated concentration. FIG. 9 is a graph showing the relationship between time and generated concentration.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigeki Hayashi 75-1 Shingo, Higashimatsuyama-shi, Saitama Osaka Oxygen Industry Co., Ltd. Development Center (56) References JP-A-64-82208 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) G05D 11/13 B01F 3/02 B01F 15/04

Claims (1)

(57) [Claim 1] In a method of mixing a second fluid with a first fluid at a predetermined ratio, a gas flow rate of the first fluid is measured , and the gas flow rate is measured based on the measured flow rate of the first fluid. Depending on the signal, the phase of density correction
The relational expression y = ax ^b + c (where x ｛ l / min] is the measured flow rate of the first fluid, y ｛ l / min] is the set flow rate of the second fluid, and a, b and c are the second fluid versus the second fluid. It changes depending on the ratio of one fluid, but at a constant concentration ratio of two fluids, it is an experimentally determined constant) and the value calculated based on the gas flow rate of the second fluid is set in real time and controlled. Mixing the first fluid and the second fluid at a predetermined ratio.