JP2001074531A - Flow rate detecting device, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize detection accuracy and improve reliability by accurately positioning a temperature sensitive resistor and a drilled hole formed on both surfaces of a silicon substrate. SOLUTION: The front surface 1A side of a silicon substrate 1 is provided with a diaphragm portion 4 using a part of an insulating film 2 by forming a drilled hole 9 from the rear surface 1B side. When the diaphragm portion 4 is formed, an injection portion of high concentration ion is previously formed at a position corresponding to the diaphragm portion 4 of the front surface 1A side of the silicon substrate 1. An anisotropic etching groove portion 10 in the drilled hole 9 is formed in a crystalline anisotropic etching process, then an isotropic etching process is selectively applied to the ion injection portion from the bottom side, and thereby, an isotropic selection etching groove portion 11 is formed. Thus, a temperature sensitive resistor 6 and the diaphragm portion 4 can be accurately positioned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate / flow rate detecting device (hereinafter referred to as a flow rate detecting device) which is formed by etching a silicon substrate and is preferably used for detecting a flow rate or a flow rate of, for example, air. And its manufacturing method.

[0002]

2. Description of the Related Art In general, a flow rate detecting device for detecting a flow rate of air or the like includes a silicon substrate formed of a single crystal silicon material, an insulating film provided on the front side of the silicon substrate, and a back side formed on the silicon substrate. A drilling hole drilled to a position reaching the insulating film by performing an etching process; and a portion of the insulating film located on the bottom side of the drilling hole provided on the front surface side of the silicon substrate. A thin diaphragm portion and a temperature-sensitive resistor provided on the front surface side of the silicon substrate and located on the diaphragm portion are known (for example, Japanese Patent Application Laid-Open No. Sho 62-43522).
No.).

[0003] A flow detecting device of this kind according to the prior art is:
For example, a temperature-sensitive resistor made of a metal film such as platinum is disposed at a predetermined position on the diaphragm while being thermally insulated from a surrounding silicon substrate by a diaphragm. And a power supply circuit including a detection circuit.

When the flow rate detecting device is operated, the temperature-sensitive resistor is supplied with electric power from a power supply circuit, for example, for 2 seconds.
When a fluid to be measured such as air flows in contact with the temperature-sensitive resistor in this state while being kept in a temperature equilibrium state at a constant temperature of about 00 to 300 ° C., the flow rate (flow velocity) of the temperature-sensitive resistor is detected by a detection circuit. Is detected as a change in the resistance value.

In manufacturing the flow rate detecting device, an insulating film made of, for example, silicon oxide or silicon nitride is first formed on the surface of the silicon substrate, and a temperature-sensitive resistor is formed at a predetermined position on the insulating film. In this case, an alignment mark is provided in advance on the front surface side of the silicon substrate in preparation for etching on the back surface side.

Next, a mask pattern for a perforated hole is provided at a predetermined position on the back surface side with reference to the alignment mark on the front surface side of the silicon substrate by using, for example, a double-sided exposure device. Then, the silicon substrate is subjected to a crystal anisotropic etching process from the back side using this mask pattern, thereby forming a perforated hole, for example, along the (111) plane of the silicon crystal constituting the silicon substrate. As a result, on both sides of the silicon substrate, the temperature-sensitive resistor and the perforated hole are formed in alignment with each other, and the temperature-sensitive resistor is disposed at a predetermined position on the diaphragm.

[0007]

In the prior art described above, for example, a double-sided exposure device is used to form a temperature-sensitive resistor and a perforated hole on both sides of a silicon substrate in a state where they are aligned. The temperature sensitive resistor is arranged at a predetermined position on the diaphragm.

However, in general, the positioning accuracy when using a double-sided exposure apparatus is often limited to about 10 μm, so that there is a gap between the temperature-sensitive resistor and the perforated hole (diaphragm). A displacement of about 10 μm may occur.

The silicon substrate is cut on both sides along, for example, the (100) plane of the silicon crystal, and the perforated hole has a constant inclination angle with respect to the (100) plane (1).
11) By being formed along the surface or the like, the silicon substrate extends obliquely from the back side to the front side.

As a result, if the silicon substrate is formed so as to be inclined with respect to the (100) plane due to a processing error or the like at the time of cutting, or if the thickness of the silicon substrate includes a dimensional error, the silicon substrate may be formed on the back side of the substrate. Drilled hole opening (mask pattern)
Even if the diaphragm is formed with high accuracy, the diaphragm portion located on the bottom side of the perforated hole is likely to be misaligned.

For this reason, in the prior art, the temperature-sensitive resistor is likely to be formed in a state of being displaced on the diaphragm portion due to the accumulation of the processing error of the substrate and the error at the time of the alignment by the double-sided exposure device. There is a problem in that the temperature equilibrium state when power is supplied to the temperature-sensitive resistor among a plurality of flow rate detection devices is likely to fluctuate, and the accuracy of flow rate detection varies, thereby lowering reliability.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to precisely position a temperature-sensitive resistor and a perforated hole for a diaphragm portion on both sides of a silicon substrate. It is an object of the present invention to provide a flow rate detection device and a method of manufacturing the flow rate detection device, which can be adjusted, stabilize detection accuracy, and improve reliability.

[0013]

According to a first aspect of the present invention, there is provided a flow rate detecting apparatus comprising: a silicon substrate formed of a silicon material; and an insulating substrate provided on a surface side of the silicon substrate. A film, a perforation hole drilled to a position reaching the insulating film by subjecting the silicon substrate to etching from the back side, and a portion of the insulating film located on the bottom side of the perforation hole. In a flow rate detection device comprising a thin-walled diaphragm provided on the front side of the silicon substrate and a temperature-sensitive resistor provided on the diaphragm, the perforated hole is formed by crystallizing the silicon substrate from the back side. Anisotropic etching to form an anisotropic etching groove formed halfway near the surface of the silicon substrate; and forming the anisotropic etching groove from the bottom side of the anisotropic etching groove. It is characterized by being configured by the isotropic etching groove portion formed over the back side of the insulating film by etching processing of isotropic surface side of the emission substrate.

[0014] With this configuration, for example, an ion-implanted portion into which impurity ions are implanted at a predetermined position corresponding to the diaphragm portion on the surface side of the silicon substrate is formed in advance. In contrast, isotropic etching can be selectively performed from within the anisotropic etching groove on the back surface side of the substrate. Therefore,
The isotropic etching groove can be formed at a predetermined position corresponding to the temperature-sensitive resistor, and the diaphragm on the front surface of the silicon substrate is disposed at a predetermined position by the isotropic etching groove formed from the back surface of the silicon substrate. be able to.

According to a second aspect of the present invention, the isotropic etching groove is formed such that an opening area opened on the back surface side of the insulating film is larger than an area on the bottom side of the anisotropic etching groove. ing.

Thus, even when the anisotropic etching groove is formed with a displacement, an isotropic etching groove can be formed from a bottom side to a predetermined portion of the silicon substrate.

According to a third aspect of the present invention, there is provided a method for manufacturing a flow rate detecting device, wherein a temperature-sensitive resistor is provided on a surface side of a silicon substrate made of a silicon material via an insulating film to correspond to the temperature-sensitive resistor. A method for manufacturing a flow rate detecting device, comprising: forming a perforated hole from the back side in the silicon substrate at a position to form a diaphragm portion using a portion of the insulating film located on the bottom side of the perforated hole. In the front surface side of the silicon substrate, impurity ions are previously implanted into a portion corresponding to the diaphragm portion, and a crystal anisotropic etching process is performed from the back surface side of the silicon substrate to a position reaching the ion implantation site. Forming an anisotropic etching groove in the perforated hole, and selectively performing isotropic etching on the ion-implanted portion from the bottom side of the anisotropic etching groove; It is characterized by the formation of the isotropic etching groove of said drilled hole.

Thus, before the perforation hole is formed, the formation position of the diaphragm can be determined in advance by using the ion implantation site on the surface side of the silicon substrate. An isotropic etching groove can be formed by selectively performing isotropic etching on the ion-implanted portion from within the anisotropic etching groove on the back surface of the substrate, and isotropically formed on the silicon substrate from the back surface. The diaphragm portion on the substrate surface side can be arranged at a predetermined position by the conductive etching groove.

According to the fourth aspect of the present invention, the ion implantation site is formed by implanting impurity ions at a concentration of 10 ¹⁹ to 10 ²² / cm ³ on the surface side of the silicon substrate.

Thus, when the isotropic etching groove is formed, the isotropic etching can be selectively performed only on the ion-implanted portion of the silicon substrate by utilizing the large concentration difference of the impurity ions. Selectivity can be increased.

According to the fifth aspect of the present invention, the silicon substrate is formed in the other of n-type and p-type on the base material formed in one of n-type and p-type by adding impurity ions. The surface layer is provided, and the anisotropic etching groove is formed by performing anisotropic etching from the back side of the base material in a state where a voltage is applied to the surface layer of the silicon substrate.

With this, when applying a voltage to the surface layer portion of the silicon substrate and performing a crystal anisotropic etching process on the base material portion, the surface layer portion is formed on the bottom side of the anisotropic etching groove formed in the base material portion. When the (ion implantation site) is exposed, an oxide film is formed on the exposed surface by the applied voltage. As a result, the anisotropic etching groove can be stopped only in the base material by the oxide film.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a flow rate detecting device and a method of manufacturing the same according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIGS. 1 to 6 show a first embodiment of the present invention. In the drawings, reference numeral 1 denotes a silicon substrate constituting a main body of a flow rate detecting device.
For example, it is formed using a single crystal silicon material or the like, and its front surface 1A and back surface 1B
0) It is formed substantially along the plane.

Reference numeral 2 denotes an insulating film provided on the surface 1A of the silicon substrate 1. As shown in FIGS. 2 and 3, the insulating film 2 is formed using, for example, silicon oxide, silicon nitride, or the like. The insulating film 2 is also formed on the back surface 1B of the silicon substrate 1.
Another insulating film 3 formed substantially in the same manner as described above is provided, and the insulating film 3 is provided with a square opening 3A.

Reference numeral 4 denotes a thin diaphragm portion formed in a substantially square shape by using a portion of the insulating film 2 disposed on the bottom side of a perforation hole 9 described later. The diaphragm portion 4 has a shape and a size. The position and the position are determined by an isotropic selective etching groove 11 described later. The diaphragm unit 4 thermally insulates a heating unit 5A of the heater 5 described later and a detection unit 6A of each temperature sensitive resistor 6 from the surrounding silicon substrate 1.

Reference numeral 5 denotes a heater provided on the insulating film 2 using a metal film such as platinum. The heater 5 has a substantially U-shape provided substantially at the center of the diaphragm 4 as shown in FIG. And a pair of wiring portions 5B, 5B connected to both ends of the heating portion 5A. The heater 5 heats the left and right temperature-sensitive resistors 6 and 6 using the heat generating portion 5A by being supplied with power from the outside.

Reference numerals 6 and 6 denote a pair of temperature-sensitive resistors provided on the surface 1A side of the silicon substrate 1. Each of the temperature-sensitive resistors 6 is formed on the insulating film 2 using a metal film such as platinum. , Heater 5
It is located on both the left and right sides of. Each of the temperature-sensitive resistors 6 is formed integrally with a substantially U-shaped detecting portion 6A disposed on the diaphragm portion 4 and a pair of wiring portions 6B, 6B connected to both ends of the detecting portion 6A. Have been.

When a fluid to be measured such as air flows in the direction indicated by an arrow A in FIG. 1, for example, heat is transmitted from the heater 5 to the temperature-sensitive resistor 6 via the flow. As a result, the flow rate (flow velocity) of air or the like is detected as a change in resistance value, and a detection signal is output to a detection circuit (not shown) such as a bridge circuit via the electrode pad 8 described below.

Reference numeral 7 denotes an insulating protective film that covers the heater 5 and the temperature-sensitive resistor 6. The protective film 7 is, as shown in FIGS.
For example, the insulating film 2 is formed using silicon oxide, silicon nitride, or the like.
It is provided above. Further, the protective film 7 is provided with a plurality of through holes 7A, 7A,.

Reference numerals 8, 8,... Denote a plurality of electrode pads provided on the protective film 7, each of which is made of a metal material such as aluminum.
A, the respective wiring portions 5B, 6 of the heater 5 and the temperature-sensitive resistor 6
B.

Reference numeral 9 denotes a perforated hole formed by opening the back surface 1B by etching the silicon substrate 1 from the back surface 1B side. The perforated hole 9 includes an anisotropic etching groove 10 described later, And an isotropic selective etching groove 11.

Reference numeral 10 denotes an anisotropic etching groove which forms the opening side of the perforation hole 9. As shown in FIG. 3, the anisotropic etching groove 10 is made of an insulating film using an alkaline etching solution such as KOH. By performing crystal anisotropic etching processing from the opening 3A using the mask 3 as a mask, the silicon substrate 1 is drilled to an intermediate position near the surface 1A of the silicon substrate 1.

Here, the anisotropic etching groove 10 has a rectangular opening 10 opening on the back surface 1 B of the silicon substrate 1.
A, a rectangular communication port 10B located on the bottom side of the anisotropic etching groove 10 and communicating with the isotropic selective etching groove 11, and a (111) plane of a silicon crystal constituting the silicon substrate 1, for example. Along the opening 10A and the communication port 10
B and four peripheral wall portions 10C, 10C,.
And is formed in a substantially trapezoidal pyramid shape as a whole.

The dimension a of one side of the opening 10A (the opening 3A of the insulating film 3) shown in FIG. 3 is formed larger than the dimension b of the communication port 10B. In addition, the peripheral wall portion 10C
Is, for example, about 5 seconds that the (100) plane and the (111) plane of the silicon crystal are formed with respect to the back surface 1B of the silicon substrate 1.
It is inclined by an inclination angle α of about 4.7 °.

Reference numeral 11 denotes an isotropic selective etching groove (isotropic etching groove) formed from the communication port 10B of the anisotropic etching groove 10 to a position opened on the back side of the insulating film 2. The etching groove portion 11 isotropically etches an ion implantation portion 21 formed in advance on the surface 1A side of the silicon substrate 1 as described later, and selectively removes the ion implantation portion 21 of the silicon substrate 1. It is formed by.

Here, the isotropic selective etching groove 11
Is formed in a substantially square shape having one side dimension c as shown in FIG. 3, and this dimension c is predetermined so as to be larger than the dimension b of the anisotropic etching groove 10 (c
> B). As a result, the opening area of the isotropic selective etching groove 11 opening on the back surface side of the insulating film 2 is formed to be larger than the area of the bottom side of the anisotropic etching groove 10 (the opening area of the communication port 10B).

The isotropic selective etching groove 11 4
The peripheral walls of the sides are, for example, curved surface portions 11A, 11A,... Formed in a concave curved shape different from the (111) plane of the silicon crystal.
The communication port 10B is disposed outside the communication port 10B.

The flow rate detecting device according to the present embodiment has the above-described configuration, and its operation will be described below.

First, when power is supplied to the heater 5, the detecting portion 6A of each temperature-sensitive resistor 6 is brought into a constant temperature equilibrium state by the heat transmitted from the heating portion 5A, and has a resistance value corresponding to the temperature. When air or the like flows in the direction indicated by the arrow A in FIG. 1 in this state, the air flows from the heater 5 between the left and right detectors 6A and 6A on the upstream and downstream sides of the flow. Since a difference in temperature (resistance value) occurs depending on the amount of heat transmitted through the flow, this difference in resistance value is detected as an air flow rate by a detection circuit.

Next, a method for manufacturing the flow rate detecting device according to the present embodiment will be described with reference to FIGS.

First, in the ion implantation step shown in FIG. 4, impurity ions such as boron are implanted into a predetermined portion of the surface 1A of the silicon substrate 1 prepared in advance corresponding to the position where the diaphragm portion 4 is formed. Inject at a high concentration of ¹⁹ / cm ³ or more and form a substantially square p with one side dimension c.
Forming an ion implantation region 21 in the form (p ⁺ form).

In this case, ions are implanted into the ion implantation site 21 at a high concentration of, for example, about 10 ¹⁹ to 10 ²² / cm ³ . In the ion implantation step, a positioning mark 22 composed of, for example, a concave hole, a projection, or the like is provided in advance at a predetermined position on the surface 1A of the silicon substrate 1.

Next, in the resistor forming step shown in FIG. 5, first, the silicon substrate 1 is formed using, for example, a thermal oxidation method, a CVD method, or the like.
After the insulating films 2 and 3 are formed, the heater 5 and each temperature-sensitive resistor 6 are simultaneously formed on the insulating film 2 by using a sputtering method, a CVD method, or the like, and a protective film 7 covering these is formed. Then, after forming each through hole 7A in the protective film 7, each electrode pad 8 is formed on the protective film 7.

Next, in the anisotropic etching step shown in FIG. 6, for example, a double-sided exposure device (not shown) or the like is used to refer to the traces of the alignment marks 22 and the like, and the insulating film 3 on the back side is used.
Is etched to form an opening 3A at a predetermined position. In this case, the position and the dimension a of the opening 3A are determined in advance so that the communication port 10B of the anisotropic etching groove 10 is arranged substantially at the center of the ion implantation part 21.

Then, the silicon substrate 1 is subjected to crystal anisotropic etching from the opening 3 A of the insulating film 3 using an alkaline etching solution such as KOH or the like, so that the anisotropic etching groove 10 reaches the position where the ion implantation site 21 is reached. Form up to. As a result, the ion implantation site 21 is exposed in the communication port 10B of the anisotropic etching groove 10.

Next, in the isotropic etching step, an etching solution formed by mixing, for example, hydrofluoric acid, nitric acid, acetic acid and the like at a fixed ratio is brought into contact with the back surface 1B side of the silicon substrate 1. Thereby, as shown in FIG. 2, in the silicon substrate 1, only the ion-implanted portion 21 is selectively removed by isotropic etching using a large concentration difference of impurity ions, and the isotropic selective etching groove portion 11 is formed. Is formed.

Thus, in the present embodiment, the perforated hole 9 formed on the back surface 1B side of the silicon substrate 1 is formed with the anisotropic etching groove 10 formed by performing the crystal anisotropic etching. Since it is composed of the isotropic etching groove portion 11 formed by selectively performing isotropic etching processing on the formed ion implantation portion 21, the diaphragm portion 4 on the surface 1 </ b> A side of the silicon substrate 1 is formed. By forming ion implantation sites 21 at corresponding predetermined positions in advance, isotropic etching is selectively performed on the ion implantation sites 21 from within the anisotropic etching groove 10 on the back surface 1B side. Therefore, the isotropic selective etching groove 11 can be formed at a predetermined position.

Even if the anisotropic etching groove 10 is displaced due to, for example, an error in alignment by the double-sided exposure apparatus or a processing error of the silicon substrate 1, this displacement is corrected by the isotropic selective etching groove 11. Compensation can be surely made, and the diaphragm portion 4 can be accurately arranged at a predetermined position.

That is, for example, when both surfaces of the silicon substrate 1 are formed so as to be inclined with respect to the (100) plane of the silicon crystal due to a processing error or the like, the (111) plane or the like is also shifted from a predetermined position. Therefore, when a crystal anisotropic etching process is performed from the back surface 1B side of the silicon substrate 1, the original etching groove portion 10 becomes, for example, an etching groove portion 10 'as shown by a virtual line in FIG. It is formed in a state where it is formed.

However, in the present embodiment, since the formation position of the isotropic selective etching groove 11 is predetermined by the ion implantation part 21 formed in the ion implantation step, the position is shifted as the etching groove 10 ′. Even in this case, in the isotropic etching step, the isotropic selective etching groove 11 can be formed at an accurate position.

Therefore, the diaphragm section 4 can be positioned with high accuracy with respect to the heater 5 and the temperature-sensitive resistor 6, and when the heater 5 is supplied with power between the plurality of flow rate detecting devices, the temperature-sensitive resistor 6 can be positioned. The temperature equilibrium state can be kept constant, and the detection accuracy of the flow rate can be stabilized to improve the reliability.

In this case, in the ion implantation step, for example, impurity ions such as boron are implanted into the surface 1A side of the silicon substrate 1 so that the diaphragm portion 4 is formed by using the ion implantation portion 21 before the perforation hole 9 is formed. Can be determined in advance.

Then, the ion implantation site 21 is
Since it is formed with a high impurity ion concentration of about 0 ¹⁹ to 10 ²² / cm ³ , in the isotropic etching step, a large difference in the concentration of the impurity ions is used to make only the ion-implanted portion 21 of the silicon substrate 1 isotropic. The selective etching process can be performed selectively, and the selectivity can be increased to improve the precision of forming the isotropic selective etching groove 11.

Since the dimension c of the ion implantation site 21 is set to be larger than the dimension b of the communication port 10B of the anisotropic etching groove 10, the size of the silicon substrate 1 at the end of the anisotropic etching step is reduced. Even when the anisotropic etching groove 10 is formed with a misalignment due to a processing error or the like, the ion implantation site 21 can be stably exposed in the communication port 10B, and the isotropic etching process is performed smoothly. be able to.

FIGS. 7 and 8 show a second embodiment according to the present invention.
In this embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

Reference numeral 31 denotes a silicon substrate of the flow rate detecting device according to the present embodiment. The silicon substrate 31 is formed of a base material portion 31A formed as a p-type single crystal silicon plate by adding impurity ions such as boron. And a surface layer portion 31 integrally formed on the base material portion 31A as an n-type single crystal silicon layer by adding impurity ions such as phosphorus.
B.

Although the perforated hole 32 is formed substantially in the same manner as the perforated hole 9 according to the first embodiment, the anisotropic etching groove 33 is formed in the base material portion 31 of the silicon substrate 31.
A, and an isotropic selective etching groove 34 is formed in the surface layer 31B.

In the manufacturing method of the flow rate detecting device thus configured, first, the ion implantation step, the resistor formation step, the anisotropic etching step and the isotropic etching step are performed in substantially the same procedure as in the first embodiment. I do.

In this case, in the ion implantation step, impurity ions such as phosphorus are implanted into the surface layer portion 31B of the silicon substrate 31 at a higher concentration, and the n-type shown in FIG. An (n ^{+ type} ) ion implantation site 35 is formed.

Then, in the anisotropic etching step, FIG.
As shown in the figure, with respect to the surface layer portion 31B of the silicon substrate 31,
DC power supply 36 and electrode 3 made of platinum or the like immersed in an etching solution
7 and the DC power supply 36 is used to connect the
For example, a voltage higher than the electrode 37 by about 0.4 to 0.6 V is applied.

In this state, the base material portion 31A of the silicon substrate 31 is formed using an alkaline etching solution such as KOH.
When the crystal layer is anisotropically etched, when the surface layer portion 31B (ion implanted portion 35) is exposed in the etching solution on the bottom side of the anisotropic etching groove portion 33, the exposed surface is exposed by the applied voltage of the DC power supply 36. A thin film of silicon oxide is formed, which covers the ion-implanted portion 35 from being etched by a crystal anisotropic process.

Thus, in the present embodiment configured as described above, substantially the same operation and effect as those of the first embodiment can be obtained. And especially in this embodiment,
In the anisotropic etching step, a p-type base material portion 31A is subjected to crystal anisotropic etching while applying a DC positive voltage to the n-type surface layer portion 31B.

By using the difference in reactivity between the base material portion 31A and the surface layer portion 31B with respect to the etching solution, for example, the exposed surface of the ion-implanted portion 35 is exposed to the oxide film when the ion-implanted portion 35 is exposed in the etching solution. And the crystal anisotropic etching can be selectively performed with high accuracy only on the base material portion 31A.

Next, FIG. 9 shows a third embodiment according to the present invention. In this embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be given. It shall be omitted.

Reference numeral 41 denotes a silicon substrate of the flow rate detecting device according to the present embodiment. The silicon substrate 41 is formed of a base material portion 41A formed as an n-type single crystal silicon plate by adding impurity ions such as phosphorus. And a surface layer portion 41 integrally formed on the base material portion 41A as a p-type single crystal silicon layer by adding impurity ions such as boron.
B.

The perforated hole 42 has an anisotropic etching groove 43 formed in the base material 41A of the silicon substrate 41, and an isotropic selective etching groove 44 formed in the surface layer 41B.

In the manufacturing method of the flow rate detecting device thus configured, first, in the ion implantation step, impurity ions such as boron are implanted at a higher concentration into the surface layer portion 41B of the silicon substrate 41, and the diaphragm portion 4 is formed. A p-type (p ^{+ -type} ) ion implantation part 45 is formed at a position corresponding to

In the anisotropic etching step, the AC power supply 46 is applied to the surface layer 41B of the silicon substrate 41.
And an electrode 47 made of platinum or the like immersed in an etching solution, and an AC voltage that changes to a higher voltage side than the electrode 47 is applied to the surface layer portion 41B using the AC power supply 46.

In this state, the base material portion 4 of the silicon substrate 41
When a crystal anisotropic etching process is performed on 1A, when the surface layer portion 41B (the ion-implanted portion 45) is exposed in the etching solution, a thin film of silicon oxide covering the exposed surface is slightly formed. The entry portion 45 is prevented from being subjected to crystal anisotropic etching.

Thus, in the present embodiment configured as described above, substantially the same operation and effect as in the first embodiment can be obtained. And especially in this embodiment,
In the anisotropic etching step, an n-type base material 41A is subjected to crystal anisotropic etching while applying a positive AC voltage to the p-type surface layer 41B.

As a result, when the ion-implanted portion 45 is exposed in the etching solution, the exposed surface can be covered with the oxide film, and the crystal anisotropic etching process can be performed with high precision only on the base material portion 41A. It can be selectively applied.

In each of the above embodiments, the diaphragm portion 4 is formed using the single insulating film 2 made of, for example, silicon oxide, silicon nitride, or the like. However, the present invention is not limited to this. Alternatively, an insulating film such as silicon oxide and an insulating film such as silicon nitride may be provided in layers, and a diaphragm portion may be formed by these insulating films.

[0074]

As described in detail above, according to the first aspect of the present invention, the perforated hole for the diaphragm is formed by the anisotropic etching groove formed by crystal anisotropic etching. Since it is constituted by an isotropic etching groove formed by performing an isotropic etching process from the inside of the groove, for example, by forming an ion implantation site in advance on the surface side of the silicon substrate, Thus, isotropic etching can be selectively performed from within the anisotropic etching groove on the back surface side. This allows
Even when the anisotropic etching groove is formed with a displacement, the isotropic etching groove can be accurately formed at a predetermined position. Therefore, the diaphragm can be positioned with high accuracy with respect to the temperature-sensitive resistor, and the temperature-balanced state of the temperature-sensitive resistor can be kept constant among a plurality of flow rate detectors, and the flow rate detection accuracy can be stabilized. And the reliability can be improved.

According to the second aspect of the present invention, the opening area of the isotropic etching groove opening on the back surface side of the insulating film is formed to be larger than the area of the bottom of the anisotropic etching groove. Even when the anisotropic etching groove is misaligned, the isotropic etching groove can be formed smoothly from a bottom side to a predetermined portion of the silicon substrate, and the anisotropic etching groove is misaligned. Compensation can be ensured by the conductive etching groove.

On the other hand, according to the third aspect of the present invention, impurity ions are implanted in advance into a portion corresponding to the diaphragm portion on the front surface side of the silicon substrate, and ion implantation portions are formed from inside the anisotropic etching groove formed on the back surface side of the substrate. In order to form an isotropic etching groove by selectively performing an isotropic etching process on the silicon substrate, an ion implantation site is used on the surface side of the silicon substrate before forming a perforation hole. The formation position can be determined in advance, and even when the anisotropic etching groove is misaligned, the isotropic etching groove can be accurately formed at a predetermined position using the ion-implanted portion. Therefore, the diaphragm can be positioned with high accuracy with respect to the temperature-sensitive resistor, and the accuracy of detecting the flow rate among the plurality of flow rate detection devices can be stabilized to improve the reliability.

According to the fourth aspect of the present invention, an ion implantation site is formed by implanting impurity ions at a concentration of 10 ¹⁹ to 10 ²² / cm ³ on the surface side of the silicon substrate. By utilizing the large concentration difference of impurity ions, it is possible to selectively perform isotropic etching only on the ion-implanted portion of the silicon substrate, and to enhance the selectivity to improve the accuracy of forming the isotropic etching groove. Can be improved.

Further, according to the fifth aspect of the present invention, the anisotropic etching groove is formed by subjecting the base material to crystal anisotropic etching from the back side while applying a voltage to the surface layer of the silicon substrate. Therefore, when applying a voltage to the surface layer portion of the silicon substrate and performing crystal anisotropic etching on the base material portion, the surface layer portion (ion-implanted portion) is exposed at the bottom side of the anisotropic etching groove. Then, an oxide film can be formed on the exposed surface by the applied voltage, and the oxide film allows the crystal anisotropic etching to be selectively performed only on the base material portion with high accuracy.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a flow detection device according to a first embodiment.

FIG. 2 is a longitudinal sectional view of the flow rate detection device viewed from the direction of arrows II-II in FIG.

FIG. 3 is an enlarged sectional view showing a perforated hole in FIG. 2 in an enlarged manner.

FIG. 4 is a longitudinal sectional view showing a state in which impurity ions are implanted into the surface side of the silicon substrate in an ion implantation step.

FIG. 5 is a longitudinal sectional view showing a state in which a temperature-sensitive resistor or the like is formed on the surface side of a silicon substrate in a resistor forming step.

FIG. 6 is a longitudinal sectional view showing a state in which a silicon substrate is subjected to crystal anisotropic etching from the back surface side in an anisotropic etching step.

FIG. 7 is a longitudinal sectional view showing a flow rate detection device according to a second embodiment.

FIG. 8 is a longitudinal sectional view showing a state in which a crystal anisotropic etching process is performed while applying a voltage to a silicon substrate in an anisotropic etching step.

FIG. 9 is a longitudinal sectional view showing an anisotropic etching process of a flow rate detecting device according to a third embodiment.

[Explanation of symbols]

1, 31, 41 Silicon substrate 2 Insulating film 4 Diaphragm 6 Temperature sensitive resistor 9, 32, 42 Perforated hole 10 Anisotropic etching groove 11 Isotropic selective etching groove (isotropic etching groove) 21, 35, 45 Ion implantation site 31A, 41A Base material 31B, 41B Surface layer

Claims (5)

[Claims] 1. A silicon substrate formed of a silicon material, an insulating film provided on a front surface side of the silicon substrate, and an etching process performed on the silicon substrate from a back surface to a position reaching the insulating film. A thin-walled diaphragm provided on the front side of the silicon substrate using a portion of the insulating film located on the bottom side of the hole, and a thin-walled diaphragm provided on the diaphragm. In the flow rate detecting device including a temperature-sensitive resistor, the perforated hole is formed to an intermediate position near the front surface of the silicon substrate by subjecting the silicon substrate to a crystal anisotropic etching process from a back surface side. An isotropic etching groove and an isotropic etching process from the bottom side of the anisotropic etching groove to the front side of the silicon substrate are performed to cover the back side of the insulating film. Flow rate detecting apparatus characterized by being configured by the by isotropic etching groove forming Te. 2. The method according to claim 1, wherein the isotropic etching groove is formed such that an opening area opening on a back surface side of the insulating film is larger than a bottom area of the anisotropic etching groove. Flow rate detection device. 3. A temperature-sensitive resistor is provided on a front side of a silicon substrate made of a silicon material via an insulating film, and a hole is formed in the silicon substrate from a back side at a position corresponding to the temperature-sensitive resistor. A method of manufacturing a flow rate detection device, wherein a diaphragm portion is formed using a portion of the insulating film located on the bottom side of the perforated hole, wherein the portion corresponding to the diaphragm portion on the front surface side of the silicon substrate is formed. Impurity ions are implanted in advance into a portion to be formed, and anisotropic etching is performed from the back surface side of the silicon substrate to a position reaching the ion implantation portion to form an anisotropic etching groove portion of the perforated hole. Then, an isotropic etching process was selectively performed on the ion-implanted portion from the bottom side of the anisotropic etching groove to form an isotropic etching groove of the perforated hole. Method of manufacturing a flow sensing device comprising and. 4. The method according to claim 1, wherein the surface of the silicon substrate has 10 ¹⁹
4. The method according to claim 3, wherein the ion implantation site is formed by implanting impurity ions at a concentration of 10 to ²² ions / cm ³ . 5. The silicon substrate is provided with a surface layer formed on the other of n-type or p-type on a base material formed on one of n-type or p-type by adding impurity ions, and The flow rate according to claim 3, wherein the anisotropic etching groove is formed by performing anisotropic etching from the back side of the base material in a state where a voltage is applied to a surface layer of the silicon substrate. Manufacturing method of the detection device.