JP4997039B2 - Flow sensor - Google Patents

Description

  The present invention relates to a flow sensor suitable for measuring a minute flow rate of gas or the like used in a semiconductor manufacturing apparatus, for example.

  For example, as a flow sensor (flow rate measuring device) that detects the flow rate of a fluid to be measured such as gas used in semiconductor manufacturing equipment, heat is applied to the fluid and the minute flow rate is measured by measuring the temperature difference of the fluid at a predetermined position. There is a thermal type flow sensor that performs (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3).

  FIG. 4 shows an example of a conventional thermal flow sensor. The thermal flow sensor 1 includes a sensor chip 4 having a flow rate detection unit 3 formed on a silicon substrate 2 and a flow rate detection unit (sensor unit) 3. It is formed by joining a glass chip 5 as a transparent flow path forming member in which a flow path (groove) 5a of the fluid flowing through the flow rate detection unit 3 is formed. The flow path 5a of the glass chip 5 is formed by sandblasting or the like.

In the inspection process after the manufacture of the flow sensor 1, it is possible to visually check whether there is any abnormality in the flow rate detection unit 3 and the flow path. Further, after use, minute dust or the like mixed with the fluid to be measured enters the flow path 5 a. It is possible to confirm whether or not the intrusion has occurred or the flow path detection unit 3 is not defective.
JP 2002-168669A (page 5-6, FIG. 1) JP 2004-325335 A (page 6-7, FIG. 8) JP 2007-071687 (page 2-3, FIG. 7)

  However, in the method of forming the flow path 5a of the glass chip 5 by sandblasting, the height from the upper surface 4a of the sensor chip 4 to the inner upper surface 5b of the flow path 5a of the glass chip 5 as shown in FIGS. It is difficult to uniformly process h (referred to as “sensor channel height”), and it is difficult to increase processing accuracy. For this reason, the cross-sectional area S (= h × w, w is the width of the flow path 5a) of the flow path 5a near the flow rate detection unit 3 may not be as designed. Since the sensor output is determined by the flow rate Q and the cross-sectional area S of the sensor flow path, if the cross-sectional area S of the flow path 5a changes, the flow characteristics (flow curve) change and a large span needs to be adjusted. As individual differences appear, it becomes difficult to achieve stable quality.

  Moreover, when the flow path 5a of the glass chip 5 is processed by sandblasting, the surface of the inner upper surface 5b of the flow path 5a, which is the processed surface, becomes rough and the transparency is deteriorated. Therefore, post-processing is required to increase transparency. Further, the pressure resistance of the glass chip may be reduced due to fine scratches during sandblasting.

  An object of the present invention is to provide a flow sensor that stabilizes the flow rate detection accuracy by improving the processing accuracy of the cross-sectional area of the sensor flow path and reducing individual differences.

In order to solve the above-described problems, a flow sensor according to the present invention is
A sensor chip in which a flow rate detection unit is formed on an insulating film coated so as to cover at least a part of a recess formed on the upper surface of the substrate;
In a flow sensor configured by joining a flow path forming member provided on the sensor chip and formed with a flow path of fluid flowing through the flow rate detection unit,
The flow path forming member is configured by joining a first flow path forming member, which is a transparent member, and a second flow path forming member,
The first flow path forming member has a plate shape, and the first flow path forming member is provided with an introduction hole and a discharge hole for the fluid to be measured.
The second flow path forming member is composed of a plate-like body formed of silicon in a predetermined shape , and the second flow path forming member has a flow along the flow of the fluid flowing along the flow rate detection unit. A through hole of a predetermined shape that forms a path is provided,
Both ends of the through-hole communicate with the introduction hole and the lead-out hole, respectively, and the flow rate detection unit is disposed between portions corresponding to the introduction hole and the lead-out hole of the through-hole,
A flow path having a predetermined cross-sectional area is formed by the first and second flow path forming members.

  The flow path forming member is a transparent plate-like first flow path forming member in which a fluid introduction hole and a lead-out hole are formed, and a fluid flow that flows along a flow rate detector provided in the sensor chip. And a second flow path forming member provided with a through-hole that forms a flow path along the flow path, and the flow path having a predetermined cross-sectional area by connecting both ends of the through-hole to the introduction hole and the discharge hole, respectively. Form a flow rate detector at the through hole. Thereby, the height of the sensor flow path, that is, the cross-sectional area of the through hole can be made constant, and the individual difference of the sensor related to the cross-sectional area of the flow path is reduced. As a result, the quality of the flow sensor can be stabilized while ensuring the transparency of the first flow path forming member.

In addition, since the sensor chip and the second flow path forming member are joined, the sensor chip and the second flow path forming member are made of materials having the same or close thermal expansion coefficient as each other. Even if the temperature around the flow path forming member changes, the sensor chip and the second flow path forming member are hardly distorted, the sensor output is less likely to drift, and deterioration of the sensor measurement accuracy is avoided. Will be able to .

In addition, by using a silicon material having the same thermal expansion coefficient as the sensor chip and the second flow path forming member or using a borosilicate glass whose thermal expansion coefficient is substantially similar to the silicon material, Due to changes in the temperature around the sensor chip and the second flow path forming member, the sensor chip and the second flow path forming member are less likely to be distorted, the sensor output is less likely to drift, and the sensor measurement accuracy is degraded. Can be avoided.

  In particular, the silicon material is a material that can improve the processing accuracy, and the processing accuracy of the second flow path forming member can be improved and can be manufactured as designed. As a result, the height of the sensor flow path is made uniform. Can be as designed. Thereby, a flow-path cross-sectional area can be made as designed, and the flow volume detection accuracy of a flow sensor can be stabilized.

A flow sensor according to claim 2 of the present invention is the flow sensor according to claim 1 ,
The first flow path forming member is made of borosilicate glass .

  The borosilicate glass of the first flow path forming member and the silicon material or borosilicate glass of the second flow path forming member have substantially the same or the same thermal expansion coefficient, and the first flow path forming member and Due to a change in temperature around the second flow path forming member, the first flow path forming member and the second flow path forming member are less likely to be distorted, and the distortion is caused to pass through the second flow path forming member. Therefore, it is difficult for the sensor output to drift, and deterioration of the measurement accuracy of the sensor can be avoided.

  According to the present invention, the flow rate detection accuracy of the flow sensor can be stabilized by improving the processing accuracy of the cross-sectional area of the sensor flow path and reducing individual differences.

  More specifically, a plate-like first flow path forming member in which a fluid introduction hole and a lead-out hole are formed, and a fluid flow that flows along a flow rate detection unit provided in the sensor chip. The flow path forming member is formed by the second flow path forming member provided with the through-hole that forms the flow path, and both ends of the through-hole are communicated with the introduction hole and the outlet hole to form the flow path. As a result, the cross-sectional area of the flow path becomes constant, individual differences among the flow sensors can be reduced, and the flow rate detection accuracy can be stabilized.

  Hereinafter, a flow sensor according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an assembled perspective view showing a flow sensor according to the present invention. The flow sensor 11 is formed by a sensor chip 12, a first flow path forming member (glass chip) 14 that forms a flow path forming member 13, and a second flow path forming member 15.

  In the sensor chip 12, a silicon nitride or silicon dioxide insulating film (thin film) 22 is formed on an upper surface 21 a of a rectangular parallelepiped silicon substrate 21, and a flow rate detection unit (sensor unit) 23 is formed at the position of the insulating film 22. Further, the flow rate detector 23 is covered with an insulating film 24 of silicon nitride or silicon dioxide. In FIG. 1, the insulating films 22 and 24 are drawn transparently so that the flow rate detection unit 23 can be easily understood.

  As shown in FIGS. 2 and 3, a recess 21 c is formed below the flow rate detector 23 at the center position of the upper surface 21 a of the silicon substrate 21, and the recess of the insulating film 22 in which the flow rate detector 23 is formed. The part covering 21c is a diaphragm, and the flow rate detector 23 and the silicon substrate 21 are thermally blocked. The flow rate detection unit 23 is a thermal detection unit and is disposed on the insulating film 22 as a heating element (not shown) made of, for example, a platinum (Pt) thin film, and arranged at equal intervals on the upstream side and the downstream side of the heater. For example, it is constituted by a temperature measuring element (not shown) as a resistance element made of a platinum thin film.

  The lead patterns 23 a, 23 b, and 23 c as signal extraction wirings of the heater and the temperature measuring element of the flow rate detection unit 23 are extended to both side surface positions of the silicon substrate 21. The tip portions of these lead patterns 23a to 23c can be connected to an external measurement circuit (not shown).

  The first flow path forming member 14 has the same size as the upper surface 21a of the silicon substrate 21 and a predetermined plate thickness, and introduces a fluid to be measured 14c at both side positions on the center line along the longitudinal direction of the upper surface 14a. The lead-out hole 14d is formed to penetrate to the lower surface 14b. These introduction holes 14c and lead-out holes 14d have the same size. Further, notches 14f are provided on both side surfaces at positions corresponding to the lead patterns 23a to 23c of the flow rate detector 23, and the external measurement circuit is exposed by exposing the connecting portions at the tips of these lead patterns 23a to 23c. It is possible to connect to. The first flow path forming member 14 is formed of transparent borosilicate glass, and the introduction hole 14c and the lead-out hole 14d are formed by mechanical processing such as sandblasting and end milling, and are finished by wet etching or dry etching. It has come to be.

  Further, since the first flow path forming member 14 only forms the fluid introduction hole 14c and the lead-out hole 14d, even when the first flow path forming member 14 is processed by sandblasting, the portion between the lead-in hole 14c and the lead-out hole 14d is formed. Transparency is ensured. Thereby, the visibility from the exterior of the flow volume detection part 23 is ensured.

  Examples of borosilicate glass include glass called Pyrex (registered trademark) glass or Tempax glass. In this embodiment, transparent Pyrex (registered trademark) glass is used. Thereby, the transparency of the first flow path forming member 14 can be ensured. In addition, transparency can be secured in the same way even with Tempax glass.

  The second flow path forming member 15 is a rectangular plate having the same size as that of the first flow path forming member 14, and has a long oval shape along the longitudinal direction on the center line along the longitudinal direction of the upper surface 15a. A long hole (track-shaped circle) 15c is formed to penetrate to the lower surface 15b (hereinafter referred to as “through-hole 15c”). The through-hole 15c has the same width as the diameter of the introduction hole 14c and the lead-out hole 14d, and the semicircular portions 15d and 15e at both ends coincide with the semicircular portions at both ends of the lead-in hole 14c and the lead-out hole 14d. It is formed to do. Further, notches 15f having the same shape are formed on both side surfaces corresponding to the notches 14f of the first flow path forming member 14, and the connecting portions at the tips of the lead patterns 23a to 23c of the flow rate detecting portion 23 are exposed. Can be connected to the external measurement circuit.

  The width of the through-hole 15 c is wider than the width of the flow rate detector 23 formed on the upper surface 12 a of the sensor chip 12. The through-hole 15c is formed by mechanical processing such as sand blasting or end milling, and may be finished by wet etching or dry etching.

  The second flow path forming member 15 is formed of a silicon plate, and the through-hole 15 c is a flow path for fluid flowing on the flow rate detection unit 23 formed on the sensor chip 12. By forming the second flow path forming member 15 with a silicon plate, the thickness can be accurately processed to a constant thickness. As a result, the depth of the through-hole 15c, that is, the height h of the sensor channel can be accurately formed, and the channel cross-sectional area can be accurately formed.

  There are two reasons for using a silicon member as the second flow path forming member. The first reason is that the processing accuracy is good, so the cross-sectional area of the sensor flow path near the flow rate detection unit 23 is as designed as compared with the prior art. It can be formed. The second reason is that since the sensor chip 12 is made of silicon and the first flow path forming member 14 is made of borosilicate glass, the thermal expansion coefficient of silicon that is the material of the sensor chip 12 is increased. This is because it is preferably a close substance and a substance close to the thermal expansion coefficient of borosilicate glass.

Since the sensor chip and the second flow path forming member are joined, it is preferable that the sensor chip 12 and the second flow path forming member 15 are made of materials having a thermal expansion coefficient close to each other. If the coefficients are close, the sensor chip 12 and the insulating material are less likely to be distorted due to temperature changes around the sensor chip 12 and the insulating material, etc., so that the output of the flow sensor is less likely to drift and the measurement accuracy of the sensor is degraded. This is because it can be avoided. Incidentally, the thermal expansion coefficient of Pyrex (registered trademark) glass is 3.2 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of silicon is 2.3 × 10 ⁻⁶ / ° C.

  Next, a procedure for manufacturing the flow sensor 11 will be briefly described. As shown in FIGS. 1 and 2, the first flow path forming member (glass chip) 14 and the second flow path forming member (silicon) 15 are overlapped, and the lower surface 14 b of the first flow path forming member 14 and the first The flow path forming member 13 is configured by joining the upper surface 15a of the second flow path forming member 15 by a method such as anodic bonding. When the first flow path forming member (glass chip) 14 and the second flow path forming member (silicon) 15 are aligned, the introduction formed in the first flow path forming member (glass chip) 14 is performed. The hole 14c and the lead-out hole 14d are in communication with both ends of the through-hole 15c formed in the second flow path forming member (silicon) 15, and the mutual members so that the notches 14f and 15f on both sides match. Place.

  In the anodic bonding, which is a bonding method in the above process, the first flow path forming member (glass chip) 14 and the second flow path forming member (silicon) 15 are used as wafers, respectively. It may be performed in the previous step, or may be performed after the wafer is divided into chips.

  Incidentally, in the present embodiment, the plate thickness of the first flow path forming member (glass chip) 14 is about 0.5 to 1.0 mm, and the second flow that becomes the height (h) of the sensor flow path. The thickness of the path forming member (silicon plate) is about 0.2 to 1.0 mm, and the size of the sensor chip 12 is about 1.5 mm × 3.5 mm to 6.0 mm × 12.0 mm. .

  Next, the flow path forming member 13 formed as described above is placed on the upper surface 12 a of the sensor chip 12, and the flow rate detection unit 23 is disposed at a substantially central position in the through-hole 15 c of the second flow path forming member (silicon) 15. Is positioned so that the top surface of the lead pattern 23a to 23c of the flow rate detection unit 23 is exposed from the notches 15f and 14f. Then, the lower surface 15b of the second flow path forming member (silicon) 15 and the upper surface 12a of the sensor chip 12 (the upper surface 21a of the silicon substrate 21) are bonded by a method such as anodic bonding.

  Thereby, since the flow volume detection part 23 is arrange | positioned in the through-hole 15c which comprises a part of sensor flow path, the to-be-measured fluid can be measured and the 1st flow path formation member which is a transparent member The flow rate detection unit 23 can be visually recognized from the outside of the flow sensor 11 through the (glass chip) 14.

  A flow path of the flow sensor 11 is formed by an introduction hole 14c and a lead-out hole 14d of the first flow path forming member (glass chip) 14 and a through-hole 15c of the second flow path forming member (silicon) 15 in communication therewith. Composed. The sensor flow path refers to the flow path of the flow sensor 11 that is configured by the through-hole 15 c of the second flow path forming member 15. In this way, the flow sensor 11 is configured.

  The flow sensor 11 is attached to, for example, a semiconductor manufacturing apparatus (not shown), and the introduction hole 14c and the discharge hole 14d of the first flow path forming member (glass chip) 14 are hermetically communicated with the fluid passage to be measured of the apparatus. The fluid to be measured flows as shown by the arrows in FIG. Moreover, each lead pattern 23a-23c of the flow sensor 11 shown in FIG. 1 is connected to the measurement circuit which is not shown in figure.

  The fluid to be measured is introduced into the through-hole 15c as a flow path from the introduction hole 14c, flows through the through-hole 15c, and is led out from the lead-out hole 14d. Then, the heater of the flow rate detector 23 is energized. The heater is heated to a certain temperature higher than the temperature of the gas measured by the ambient temperature sensor provided on the silicon substrate 21 by the control circuit, and heats the gas flowing through the through-hole (flow path) 15c.

  When the gas does not flow, a uniform temperature distribution is formed on the upstream / downstream side of the heater, and the upstream temperature measuring element and the downstream temperature measuring element show resistance values corresponding to substantially equal temperatures. . On the other hand, when there is a gas flow, the balance of the uniform temperature distribution on the upstream / downstream side of the heater is lost, the temperature on the upstream side decreases, and the temperature on the downstream side increases. Then, a resistance value difference of the temperature measuring element, that is, a temperature difference equivalent to this is detected by, for example, a Wheatstone bridge circuit composed of the temperature measuring element on the upstream side and the temperature measuring element on the downstream side, and a through-hole ( (Flow path) The flow rate of the gas flowing in 15c is measured.

  In the above embodiment, the case where the indirectly heated flow rate detection unit is configured by one heater (heating element) and two temperature measuring elements arranged on both sides of the heater has been described. However, the present invention is not limited to this. Rather, one heat generating element, that is, one heater may constitute a self-heating type flow rate detecting unit, or two heat generating elements, that is, two heaters, constitute a self-heating type flow rate detecting unit. May be.

  In addition, in the range which does not deviate from the meaning of this invention, you may use the 2nd flow path formation member near a sensor chip and a thermal expansion coefficient according to the material of a sensor chip. For example, the material of the first flow path detection member and the second flow path detection member can also be formed of borosilicate glass. Borosilicate glass is a material with good flatness and easy to process, and can be easily used.

  As described above, according to the present invention, the flow path forming member is provided with the transparent plate-like first flow path forming member in which the fluid introduction hole and the lead-out hole are formed, and is provided on the sensor chip. It is formed by joining a second flow path forming member provided with a through hole that forms a flow path along the flow of the fluid flowing along the flow rate detection unit, and introduces both ends of the through hole (flow path) A flow passage having a predetermined flow passage cross-sectional area is formed by communicating with each of the hole and the lead-out hole, and a flow rate detection unit is disposed in the through-hole, thereby making the height of the sensor flow passage, that is, the cross-sectional area of the through-hole constant. Can be. As a result, it is possible to reduce individual differences between the sensors regarding the cross-sectional area of the flow path, and it is possible to stabilize the quality of the flow sensor.

  In addition, since the flow path is not formed in the first flow path forming member 14 by sandblasting or the like, the flow path is not damaged, and cracks and the like caused by the fine damage are prevented. It is possible to improve pressure resistance and durability, and it is possible to ensure visibility from the outside, and it is easy to inspect the presence or absence of dust in the flow path in the flow sensor manufacturing process. Become.

  In addition, since the sensor chip and the second flow path forming member are joined, the sensor chip and the second flow path forming member are made of materials having the same or close thermal expansion coefficient as each other. Since the sensor chip and the second flow path forming member are less likely to be distorted due to a change in temperature around the flow path forming member, the sensor output is less likely to drift and deterioration of the sensor measurement accuracy is avoided. Can do.

  In addition, since the sensor chip and the second flow path forming member are joined, the sensor chip and the second flow path forming member heat the silicon material having the same thermal expansion coefficient or the second flow path forming member. By using borosilicate glass whose expansion coefficient is substantially similar to that of a silicon material, the sensor chip and the second flow path forming member are distorted due to a change in temperature around the sensor chip and the second flow path forming member. It is difficult to occur, the output of the sensor is difficult to drift, and deterioration of the measurement accuracy of the sensor can be avoided.

  In particular, the silicon material is a material that can improve the processing accuracy, and the second flow path forming member also has a high processing accuracy and can be manufactured as designed. As a result, the height of the sensor flow path can be made uniform as designed, and thereby the flow path cross-sectional area can be made as designed, and the flow rate detection accuracy of the flow sensor can be stabilized.

  Further, since the borosilicate glass of the first flow path forming member and the silicon material or borosilicate glass of the second flow path forming member are joined, the borosilicate glass of the first flow path forming member and the second The silicon material or the borosilicate glass of the flow path forming member has substantially the same or the same thermal expansion coefficient, and due to temperature changes around the first flow path forming member and the second flow path forming member, The first flow path forming member and the second flow path forming member are less likely to be distorted, and the strain is not transmitted to the sensor chip via the second flow path forming member, and the sensor output drifts. It is difficult to avoid deterioration of the measurement accuracy of the sensor.

It is an assembly perspective view of the flow sensor concerning the present invention. It is sectional drawing of the state which assembled the flow sensor shown in FIG. It is sectional drawing which follows the arrow line III-III of the flow sensor shown in FIG. It is sectional drawing which shows an example of the conventional flow sensor. It is sectional drawing which follows the arrow line VV of the flow sensor shown in FIG.

Explanation of symbols

1 Flow sensor 2 Silicon substrate 3 Flow rate detection unit (sensor unit)
4 Sensor chip 4a Upper surface 5 Glass chip (channel forming member)
5a Channel (groove)
5b Inner upper surface of channel 11 Flow sensor 12 Sensor chip 12a Upper surface 12b Lower surface 13 Channel forming member 14 First channel forming member (glass chip)
14a Upper surface 14b Lower surface 14c Introducing hole 14d Deriving hole 14f Notch 15 Second flow path forming member (silicon)
15a Upper surface 15b Lower surface 15c Through-hole (flow path)
15d, 15e Semicircular part 15f Notch 21 Silicon substrate 21a Upper surface 21b Lower surface 21c Recessed part 22, 24 Insulating film 23 Flow rate detection part (sensor part)
23a, 23b, 23c Lead pattern h Sensor channel height w Channel width S Channel cross-sectional area Q Flow rate

Claims (2)

A sensor chip in which a flow rate detection unit is formed on an insulating film coated so as to cover at least a part of a recess formed on the upper surface of the substrate;
In a flow sensor configured by joining a flow path forming member provided on the sensor chip and formed with a flow path of fluid flowing through the flow rate detection unit,
The flow path forming member is configured by joining a first flow path forming member, which is a transparent member, and a second flow path forming member,
The first flow path forming member has a plate shape, and the first flow path forming member is provided with an introduction hole and a discharge hole for the fluid to be measured.
The second flow path forming member is composed of a plate-like body formed of silicon in a predetermined shape , and the second flow path forming member has a flow along the flow of the fluid flowing along the flow rate detection unit. A through hole of a predetermined shape that forms a path is provided,
Both ends of the through-hole communicate with the introduction hole and the lead-out hole, respectively, and the flow rate detection unit is disposed between portions corresponding to the introduction hole and the lead-out hole of the through-hole,
A flow sensor having a predetermined cross-sectional area formed by the first and second flow path forming members. The flow sensor according to claim 1, wherein the first flow path forming member is made of borosilicate glass .

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