JP2016075579A - Method of manufacturing physical quantity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a physical quantity sensor such that a shift in relative position between a strain detection element and an outline of a diaphram is small and sensitivity of detection of deformation of the diaphram by the strain detection element is improved.SOLUTION: A method of manufacturing a pressure sensor 1 includes: a substrate preparing process of preparing a substrate 40 having a piezoresistive element 20, strained to output a signal, arranged on the side of one surface 40a; a first etching process of etching the substrate 40 from the side of the other surface 40b in top/reverse relation with the one surface 40a including a range overlapping the piezoresistive element 20 in plan view so as to form a first recessed part 41; and a second etching process of dry-etching a bottom part of the recessed part 41 including at least a part of the range overlapping the piezoresistive element 20 in plan view so as to form a second recessed part 42 having a diaphragm 10 at its bottom, a depth H2 of the second recessed part 42 being equal to or less than a depth H1 of the first recessed part 41.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for manufacturing a physical quantity sensor.

Conventionally, as an example of a physical quantity sensor, a concave portion is formed on the back surface side, thereby forming a substantially rectangular thin bent portion (hereinafter referred to as a diaphragm) at the center portion on the front surface side, and detecting deformation of the diaphragm. A pressure sensor chip is provided with a glass pedestal formed with a through hole serving as a pressure introducing hole on the back surface of the pressure sensor chip, and the pressure sensor is joined so that the opening of the through hole is accommodated in the opening surface of the recess. There is known a semiconductor pressure sensor having a configuration in which the edge shape of a concave portion in contact with the bonding surface between a chip and a glass pedestal is substantially circular in a plan view (for example, see Patent Document 1).
In the semiconductor pressure sensor, since the edge shape of the concave portion in contact with the joint surface between the pressure sensor chip and the glass pedestal is substantially circular in plan view, the stress concentration at the time of pressure application is relaxed, and the breakdown pressure level is improved. It is said that a semiconductor pressure sensor can be provided.

JP 2002-39892 A

In the semiconductor pressure sensor, a recess is formed by etching the back side of the pressure sensor chip, and a diaphragm is formed at the bottom. Here, a step portion in the concave portion is provided, the first concave portion on the opening side is etched, and the side having the diaphragm at the bottom portion is defined as the second concave portion.
On the other hand, the pressure sensitive element for detecting the deformation of the diaphragm is formed on the surface side of the pressure sensor chip before the etching because of manufacturing restrictions.

For this reason, the semiconductor pressure sensor has an outline of the pressure-sensitive element and the diaphragm due to the displacement of the etching of the pressure sensor chip and the deviation of the traveling direction (traveling angle) of the pressure sensor chip due to the deformation of the warp of the pressure sensor chip. The relative position may be deviated from the original position.
At this time, the shift in the etching progress direction increases the shift in the relative position as the second recess becomes deeper.

According to FIG. 1B of Patent Document 1, the semiconductor pressure sensor has a depth of the second recess that is considerably deeper than the depth of the first recess.
As a result, the semiconductor pressure sensor may not be able to detect the deformation of the diaphragm by the pressure sensitive element due to the displacement of the relative position, which may cause a problem such as a decrease in pressure receiving sensitivity.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  [Application Example 1] A method of manufacturing a physical quantity sensor according to this application example includes a step of preparing a substrate on one surface side on which a strain detection element that receives a strain and outputs a signal is disposed; Etching including a range overlapping with the strain detection element in plan view from the other surface side that is in a front-back relationship with the one surface, and forming a first recess, and a bottom portion of the first recess And a second etching step of forming a second recess having a diaphragm at the bottom thereof by dry etching including at least a part of a range overlapping with the strain detection element in plan view, the depth of the second recess Is less than the depth of the first recess.

According to this, in the method of manufacturing a physical quantity sensor, a substrate having a strain detection element on one surface side is etched to include a range overlapping the strain detection element from the other surface side to form a first recess, The bottom of the first recess is dry-etched to include at least part of the range overlapping the strain detection element to form a second recess having a diaphragm at the bottom, and the depth of the second recess is less than the depth of the first recess is there.
Thereby, since the depth of the 2nd recessed part which has a diaphragm in the bottom is below the depth of a 1st recessed part, the manufacturing method of a physical quantity sensor is a distortion detection element compared with the past (for example, patent document 1). It is possible to reduce a shift in relative position between the pressure sensor and the diaphragm contour.
As a result, the physical quantity sensor manufacturing method can manufacture and provide a physical quantity sensor in which the relative position shift is small and the detection sensitivity of the deformation (distortion) of the diaphragm by the strain detection element is improved.

  In addition, since the physical quantity sensor manufacturing method forms the second concave portion by dry etching, it is less likely to enter the non-etched region during etching than the wet etching, and the shape of the second concave portion can be formed with high accuracy. .

  Application Example 2 In the method of manufacturing a physical quantity sensor according to the application example, the second etching step includes resist formation for positioning a mask with reference to a pattern provided on the one surface side of the substrate. Preferably a step is included.

  According to this, the physical quantity sensor manufacturing method includes a resist forming step of positioning the mask with reference to a pattern provided on one surface side of the same substrate as the strain detection element in the second etching step. For this reason, the displacement of the relative position between the strain detection element and the outline of the diaphragm can be further reduced as compared with the case where the pattern provided on the other surface side of the substrate is used as a reference.

  Application Example 3 In the method of manufacturing a physical quantity sensor according to the application example, it is preferable that the pattern is the strain detection element.

According to this, in the physical quantity sensor manufacturing method, since the pattern in the application example is a strain detecting element, the mask can be positioned more accurately in the resist forming step.
As a result, the physical quantity sensor manufacturing method can further reduce the displacement of the relative position between the strain detection element and the contour of the diaphragm.

  Application Example 4 In the method of manufacturing a physical quantity sensor according to the application example, it is preferable that the method further includes a step of reducing the thickness of the substrate before the first etching step.

  According to this, since the physical quantity sensor manufacturing method further includes the step of reducing the thickness of the substrate before the first etching step, the productivity can be improved as compared with the case where this step is not included.

  Application Example 5 In the method of manufacturing a physical quantity sensor according to the application example described above, a step of forming a pressure reference chamber overlapping the diaphragm in plan view on the one surface side of the substrate before the first etching step. It is preferable that it is further included.

According to this, the manufacturing method of the physical quantity sensor further includes a step of forming a pressure reference chamber that overlaps the diaphragm in plan view on one surface side of the substrate before the first etching step.
Accordingly, the physical quantity sensor manufacturing method can manufacture and provide a physical quantity sensor capable of detecting pressure based on the pressure reference chamber from the distortion of the received diaphragm.

  Application Example 6 In the physical quantity sensor manufacturing method according to the application example, the physical quantity sensor is a pressure sensor having a pressure detection function.

  According to this, since the physical quantity sensor is a pressure sensor having a pressure detection function, a pressure sensor with improved detection sensitivity of the deformation (distortion) of the diaphragm received by the strain detection element is manufactured. And can be provided.

It is a schematic diagram which shows schematic structure of the pressure sensor of 1st Embodiment, (a) is a schematic plan view, (b) is a schematic cross section in the AA of (a). The circuit diagram for a model detection of a pressure sensor. The flowchart which shows the main manufacturing processes of the manufacturing method of the pressure sensor of 1st Embodiment. (A)-(d) is a schematic cross section explaining a main manufacturing process in order. (E)-(h) is a schematic cross section explaining a main manufacturing process in order. The principal part sectional drawing of a pressure sensor. It is a schematic diagram which shows schematic structure of the pressure sensor of 2nd Embodiment, (a) is a schematic plan view, (b) is a schematic cross section in the AA of (a). The flowchart which shows the main manufacturing processes of the manufacturing method of the pressure sensor of 2nd Embodiment. (A)-(d) is a schematic cross section explaining a main manufacturing process in order. (E)-(h) is a schematic cross section explaining a main manufacturing process in order. The schematic cross section which shows schematic structure of the pressure sensor of the modification of 2nd Embodiment.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings.

(First embodiment)
First, a configuration of a pressure sensor having a pressure detection function will be described as an example of a physical quantity sensor.
FIG. 1 is a schematic diagram illustrating a schematic configuration of the pressure sensor according to the first embodiment. FIG. 1A is a schematic plan view, and FIG. 1B is a line AA in FIG. FIG. FIG. 2 is a schematic detection circuit diagram of the pressure sensor. For convenience of explanation, the dimensional ratio of each component is different from the actual one.

As shown in FIGS. 1 and 2, the pressure sensor 1 of the first embodiment includes a substrate 40 and a cavity layer 50 that covers the one surface 40 a side of the substrate 40, and the planar shape is substantially rectangular. Thus, it has a substantially rectangular parallelepiped shape.
The pressure sensor 1 is disposed on the one surface 40a side of the substrate 40, and the piezoresistive element 20 as a strain detection element that receives a strain and outputs a signal, and the one surface 40a of the substrate 40 are front-back relations. The first recess 41 provided on the other surface 40b side including a range overlapping the piezoresistive element 20 in plan view, and a range overlapping the piezoresistive element 20 in plan view at the bottom of the first recess 41 And a second recess 42 provided to include at least a part (all in this case).
The pressure sensor 1 further includes a diaphragm 10 provided at the bottom of the second recess 42 and a detection circuit 30 to which the piezoresistive element 20 is connected. In addition, the pressure sensor 1 includes a hollow pressure reference chamber S that overlaps the diaphragm 10 in plan view on the one surface 40 a side of the substrate 40.

The pressure reference chamber S is inside the cavity layer 50 and has a substantially rectangular parallelepiped shape. The diaphragm 10 has a substantially rectangular outline that is slightly smaller at the bottom of the substantially rectangular shape in plan view. Will be provided.
The pressure reference chamber S is sealed in a vacuum state (for example, a degree of vacuum of 10 Pa or less). Thereby, the pressure reference chamber S becomes a reference of the pressure detected by the pressure sensor 1, and the pressure sensor 1 functions as an absolute pressure sensor.
Note that the pressure reference chamber S may not be in a vacuum state, and may be in an atmospheric pressure state filled with an inert gas such as nitrogen, argon, or helium, for example.

  In the pressure reference chamber S, for example, an insulating film (passivation film) 46 is formed on the one surface 40a side of the substrate 40 by using a semiconductor manufacturing process, and then a sacrificial layer 51 ′ composed of an oxide film layer 51 and the like is sequentially deposited. Then, the metal layer 52 is sequentially deposited so as to surround the sacrificial layer 51 ′ and cover the sacrificial layer 51 ′, and then a plurality of through holes 53 are provided in the metal layer 52 covering the sacrificial layer 51 ′. After the selective release etching of the sacrificial layer 51 ′, the through hole 53 is provided in the cavity layer 50 by sealing with the sealing layer 54. (Here, for convenience, the inside of the pressure reference chamber S is shown as a sacrificial layer 51 '.)

The diaphragm 10 includes an SOI substrate (a substrate in which a SiO ₂ (also referred to as silicon dioxide or silicon oxide film) layer is inserted between a silicon substrate layer and a silicon layer) or a substrate 40 using a semiconductor substrate such as a silicon substrate. The first recess 41 is provided on the other surface 40 b side, and the second recess 42 is provided at the bottom of the first recess 41, thereby forming the bottom of the second recess 42. In addition, the 1st recessed part 41 and the 2nd recessed part 42 are formed in the substantially rectangular shape by planar view.
Here, an SOI substrate is used as the substrate 40, and the first recess 41 is provided by etching the silicon substrate layer 43 halfway, and the bottom of the first recess 41 is further etched until the SiO ₂ layer 44 is reached. A second recess 42 is provided.
Here, the depth H2 of the second recess 42 is equal to or less than the depth H1 of the first recess 41 (H2 ≦ H1).

The piezoresistive element 20 is formed in a substantially rectangular shape by doping (diffusing or implanting) impurities such as phosphorus and boron into the silicon layer 45 of the substrate 40. The piezoresistive element 20 has a property that the resistance value linearly changes in accordance with applied stress (distortion due to the deflection of the diaphragm 10).
The piezoresistive element 20 is provided so as to correspond to each of the four sides of the substantially rectangular outline of the diaphragm 10. (For convenience, the reference numeral 20 is used for the description of the entire piezoresistive element, and the reference numerals 21 to 24 are used for the individual description.)

The piezoresistive elements 21 to 24 are disposed inside the diaphragm 10 and in the immediate vicinity of the sides 11 to 14 of the contour.
More specifically, for the side 11 of the diaphragm 10, a piezoresistive element 21 is arranged in the vicinity of the center of the side 11 with the longitudinal direction extending along the side 11, and for the side 12 facing the side 11, the piezoresistive element 21. The resistance element 22 is arranged in the vicinity of the center of the side 12 along the side 12 in the longitudinal direction.
For the side 13 adjacent to the side 11 of the diaphragm 10, a piezoresistive element 23 is arranged near the center of the side 13 along the direction perpendicular to the side 13, and the side facing the side 13. 14, a piezoresistive element 24 is arranged in the vicinity of the center of the side 14 with its longitudinal direction being along the direction orthogonal to the side 14.
That is, the piezoresistive elements 21 to 24 are arranged so that their longitudinal directions are all the same. Note that wirings for connecting the piezoresistive elements 21 to 24 are omitted. Note that a plurality of piezoresistive elements 21 to 24 may be grouped in series.

As shown in FIG. 2, the piezoresistive elements 21 to 24 are connected to the detection circuit 30 and constitute a bridge circuit (Wheatstone bridge circuit).
The piezoresistive elements 21 to 24 are configured to have the same resistance value.
In the pressure sensor 1, a drive voltage (AVDC) is supplied from a drive circuit (not shown) to a connection portion between the piezoresistive element 23 and the piezoresistive element 22, and the piezoresistive element 21 and the piezoresistive element 24 are connected to each other. The connection is grounded.
Thus, the pressure sensor 1 outputs the midpoint potential in the detection circuit 30 to the connection part 31 between the piezoresistive element 21 and the piezoresistive element 23 and the connection part 32 between the piezoresistive element 22 and the piezoresistive element 24. Is done.

Here, the operation of the pressure sensor 1 will be described.
As shown in FIG. 2, the pressure sensor 1 is based on a potential difference between the connection portions 31-32 caused by a change in the resistance value of the piezoresistive elements 21 to 24 due to the deflection (deformation) of the diaphragm 10 when pressure is applied. The pressure value is derived.
The piezoresistive elements 21 and 22 are set so that the longitudinal direction is compressed and the resistance value is reduced by the diaphragm 10 being bent, and the piezoresistive elements 23 and 24 are set by the diaphragm 10 being bent. The longitudinal direction is extended so that the resistance value is increased.

In the pressure sensor 1, the diaphragm 10 does not bend in a state where no pressure is applied, so that the resistance values of the piezoresistive elements 21 to 24 are not changed and remain equal to each other.
As a result, in the pressure sensor 1, the potential difference between the connecting portions 31-32 becomes 0, and the derived pressure value becomes 0.

When pressure is applied from the outside to the pressure sensor 1, the diaphragm 10 bends, for example, toward the pressure reference chamber S, so that the resistance values of the piezoresistive elements 21 and 22 become small, and the piezoresistive elements 23 and 24. The resistance value increases.
As a result, in the pressure sensor 1, the midpoint potential of the connecting portions 31 and 32 changes, and a potential difference is generated between the connecting portions 31 and 32. Therefore, a pressure value corresponding to the potential difference is derived based on a lookup table or the like. Is done.
In addition, it is known that the stress produced when the diaphragm 10 bends is so large that it is close to the outline. From this, it is preferable that the piezoresistive element 20 is disposed immediately inside the contour of the diaphragm 10 in order to improve the pressure detection sensitivity (in other words, increase the change in the resistance value).

Next, an example of the manufacturing method of the pressure sensor 1 will be described.
FIG. 3 is a flowchart showing main manufacturing steps of the pressure sensor manufacturing method according to the first embodiment, and FIGS. 4A to 4D and FIGS. 5E to 5H show the main manufacturing steps. It is a schematic cross section explaining these in order. In addition, the cross-sectional position of each figure is the same as that of FIG.1 (b).

  As shown in FIG. 3, the manufacturing method of the pressure sensor 1 includes a substrate preparation step, a substrate thickness adjustment step, a pressure reference chamber formation step, a first etching step, and a second etching step. The pressure sensor 1 is manufactured using, for example, a semiconductor manufacturing process.

[Board preparation process]
First, as shown in FIG. 4A, by doping impurities such as phosphorus and boron into a predetermined position of the silicon layer 45 on the one surface 40a side of the wafer-like substrate 40, the planar shape is substantially rectangular. A piezoresistive element 20 (21 to 24) is formed.
Thus, the substrate 40 on which the piezoresistive element 20 as a strain detecting element that receives a strain and outputs a signal is arranged on one surface 40a side is prepared.

[Substrate thickness adjustment process]
Next, as shown in FIG. 4B, the other surface 40b side of the substrate 40 is shaved by using a back grinding method or the like, and is formed in a wafer shape and relatively thick so as to ensure sufficient strength. The thickness of the substrate 40 (for example, about 700 μm) is reduced to a desired thickness (for example, about 150 μm to 400 μm).

[Pressure reference chamber formation process]
Next, as shown in FIG. 4C, an insulating film 46 made of Si ₃ N ₄ (also referred to as silicon nitride or silicon nitride) or the like is formed on one surface 40a side of the substrate 40, followed by CVD or the like. A sacrificial layer 51 ′ composed of an oxide film (for example, SiO ₂ film) layer 51 or the like is sequentially deposited by using a metal layer (wiring layer) using a sputtering method or the like so as to surround the sacrificial layer 51 ′ and further cover from above. ) 52 are sequentially deposited (usually, the deposition of the sacrificial layer 51 ′ and the deposition of the metal layer 52 are alternately performed in a plurality of layers).
Next, a plurality of through holes 53 are provided in the metal layer 52 covering the sacrificial layer 51 ′, and the sacrificial layer 51 ′ is selectively release etched from the through holes 53 by dry etching or wet etching, and then in vacuum (for example, The pressure reference chamber S is formed inside the cavity layer 50 by sealing the through-hole 53 with the sealing layer 54 using a sputtering method or the like at a degree of vacuum of 10 Pa or less.
The pressure reference chamber S may not be in a vacuum state, and may be in an atmospheric pressure state filled with an inert gas such as nitrogen, argon, or helium.

[First etching step]
Next, as shown in FIG. 4D, a resist 401 is applied to the other surface 40b of the substrate 40 using a spin coating method or the like, and the resist 401 is applied to the first recess 41 (see FIG. 4) using a photolithography method or the like. 1), patterning is performed according to the planar shape.
Next, as shown in FIG. 5 (e), a step of forming a protective film with a Bosch process (c-C ₄ F ₈ (cyclobutane octafluoride) gas) and a step of etching with SF ₆ (sulfur hexafluoride) gas The silicon substrate layer 43 is etched partway from the other surface 40b side of the substrate 40 by dry etching using a process in which the first recess 41 is formed. At this time, the etching is performed including a range overlapping with the piezoresistive element 20 in plan view.
The depth H1 of the first recess 41 is at least half the thickness t of the silicon substrate layer 43 (H1 ≧ (t / 2)).

  The etching here may be wet etching using an alkaline etching solution such as a KOH (potassium hydroxide) aqueous solution, a TMAH (tetramethylammonium hydroxide) aqueous solution, or an EDP (ethylenediamine pyrocatechol) aqueous solution.

[Second etching step]
Next, as shown in FIG. 5F, after the resist 401 is peeled off, a resist 402 is formed on the other surface 40b of the substrate 40 and the first recess 41 using a CVD method or the like, and a photolithography method or the like is performed. Then, the resist 402 is patterned in accordance with the planar shape of the second recess 42 (see FIG. 1).
Next, as shown in FIG. 5G, the bottom of the first recess 41 is etched until it reaches the SiO ₂ layer 44 by dry etching using the Bosch process, thereby forming the second recess 42. At this time, the etching is performed so as to include at least part (here, all) of the range overlapping with the piezoresistive element 20 in plan view.
As a result, the diaphragm 10 is formed at the bottom of the second recess 42. In other words, the second recess 42 having the diaphragm 10 at the bottom is formed.
At this time, the depth H2 of the second recess 42 is equal to or less than the depth H1 of the first recess 41 (H2 ≦ H1).
Next, as shown in FIG. 5H, the resist 402 is stripped using a stripping agent or the like.
Through the above steps, the pressure sensor 1 shown in FIG. 1 is obtained.

As described above, the manufacturing method of the pressure sensor 1 of the first embodiment includes the range in which the substrate 40 having the piezoresistive element 20 on the one surface 40a side overlaps the piezoresistive element 20 from the other surface 40b side. The first recess 41 is formed by etching, and the bottom of the first recess 41 is dry-etched to include at least a part (here, all) of the range overlapping with the piezoresistive element 20. The recess 42 is formed, and the depth H2 of the second recess 42 is equal to or less than the depth H1 of the first recess 41 (H2 ≦ H1).
Thereby, the manufacturing method of the pressure sensor 1 is compared with the conventional method (for example, Patent Document 1) because the depth H2 of the second recess 42 having the diaphragm 10 at the bottom is equal to or less than the depth H1 of the first recess 41. Thus, the displacement of the relative position between the piezoresistive element 20 and the outline of the diaphragm 10 can be reduced.

More specifically, for example, when the substrate 40 is warped downward (when it is warped like an open umbrella), as shown in the schematic cross-sectional view of the main part of the pressure sensor in FIG. The side wall of the formed second recess 42 is inclined with respect to the SiO ₂ layer 44 rather than at a right angle.
Here, since the depth H2 of the second recess 42 is equal to or less than the depth H1 of the first recess 41 (H2 ≦ H1), the actual contour position P0 of the diaphragm 10 at the bottom of the second recess 42 is actually measured. The displacement of the contour position P1 is the original contour position of the diaphragm 10 when the depth H2 ′ of the second recess 42 exceeds the depth H1 ′ of the first recess 41 (H2 ′> H1 ′). This is smaller than the deviation of the position P2 of the virtual contour with respect to P0.
As a result, the manufacturing method of the pressure sensor 1 is a physical quantity sensor in which the displacement of the relative position between the contour of the diaphragm 10 and the piezoresistive element 20 is small and the detection sensitivity of deformation (distortion) of the diaphragm 10 by the piezoresistive element 20 is improved. Can be manufactured and provided.

  Moreover, since the manufacturing method of the pressure sensor 1 forms the 2nd recessed part 42 by dry etching, there is less wraparound to the non-etching area | region at the time of etching than wet etching, and forms the shape of the 2nd recessed part 42 accurately. be able to.

Moreover, since the manufacturing method of the pressure sensor 1 includes the substrate thickness adjusting step of reducing the thickness of the substrate 40 before the first etching step, the first etching step and the second etching are performed as compared with the case where this step is not included. The working time of the process can be shortened.
Thereby, the manufacturing method of the pressure sensor 1 can improve productivity.

In addition, the manufacturing method of the pressure sensor 1 includes a pressure reference chamber forming step of forming a hollow pressure reference chamber S that overlaps the diaphragm 10 in plan view on the one surface 40a side of the substrate 40 before the first etching step. In addition.
Thereby, the manufacturing method of the pressure sensor 1 can manufacture and provide a physical quantity sensor capable of detecting pressure based on the pressure reference chamber S from the strain of the diaphragm 10 that has received pressure.

  In addition, since the physical quantity sensor is a pressure sensor having a pressure detection function, the pressure sensor 1 is manufactured as a physical quantity sensor with improved detection sensitivity of deformation (distortion) of the diaphragm 10 received by the piezoresistive element 20. The pressure sensor 1 can be manufactured and provided.

Note that the substrate thickness adjustment step may be omitted if there is no problem with productivity. Further, when detecting the differential pressure between the one surface 40a side and the other surface 40b side of the substrate 40, the pressure reference chamber forming step is not necessary.
In addition, as for the planar shape of the 1st recessed part 41 and the 2nd recessed part 42 of the pressure sensor 1, either one or both may be substantially circular shape.

(Second Embodiment)
Next, the configuration of another pressure sensor having a pressure detection function will be described as another example of the physical quantity sensor.
FIG. 7 is a schematic diagram showing a schematic configuration of the pressure sensor according to the second embodiment. FIG. 7A is a schematic plan view, and FIG. 7B is a line AA in FIG. FIG. Note that a detailed description of portions common to the first embodiment will be omitted, and portions different from the first embodiment will be mainly described.

As shown in FIG. 7, in the pressure sensor 2 of the second embodiment, the pressure reference chamber S is provided on the other surface 40 b side of the substrate 40.
In the pressure reference chamber S of the pressure sensor 2, the first recess 41 and the second recess 42 are formed on the other surface 40 b side of the substrate 40, and then the base substrate 60 made of a glass plate, a silicon substrate or the like is used as the other substrate 40. It is provided by bonding to the surface 40b side.
The pressure reference chamber S is sealed in a vacuum state (for example, a degree of vacuum of 10 Pa or less). Thereby, the pressure reference chamber S becomes a reference of the pressure detected by the pressure sensor 2, and the pressure sensor 2 functions as an absolute pressure sensor.

Note that the pressure reference chamber S may not be in a vacuum state, and may be in an atmospheric pressure state filled with an inert gas such as nitrogen, argon, or helium, for example.
In the pressure sensor 2, an insulating film 46 (see FIG. 1) that protects the piezoresistive element 20 may be provided on one surface 40 a of the substrate 40.
Since the operation of the pressure sensor 2 is the same as that of the first embodiment, the description thereof is omitted.

Next, an example of a manufacturing method of the pressure sensor 2 will be described.
FIG. 8 is a flowchart showing main manufacturing steps of the pressure sensor manufacturing method according to the second embodiment. FIGS. 9A to 9D and FIGS. 10E to 10H are the main manufacturing steps. It is a schematic cross section explaining a process in order. In addition, the cross-sectional position of each figure is the same as that of FIG.7 (b).

  As shown in FIG. 8, the manufacturing method of the pressure sensor 2 includes a substrate preparation step, a substrate thickness adjustment step, a first etching step, a second etching step, and a pressure reference chamber forming step. The pressure sensor 2 is manufactured using, for example, a semiconductor manufacturing process.

[Board preparation process]
First, as shown in FIG. 9A, by doping impurities such as phosphorus and boron into a predetermined position of the silicon layer 45 on the one surface 40a side of the wafer-like substrate 40, the planar shape is substantially rectangular. A piezoresistive element 20 (21 to 24) is formed.
Thus, the substrate 40 on which the piezoresistive element 20 as a strain detecting element that receives a strain and outputs a signal is arranged on one surface 40a side is prepared.
Note that an insulating film 46 (see FIG. 1) may be formed on one surface 40 a of the substrate 40 after the piezoresistive element 20 is formed.

[Substrate thickness adjustment process]
Next, as shown in FIG. 9B, the other surface 40b side of the substrate 40 is shaved using a back grind method or the like, and is formed in a wafer shape and relatively thick to ensure sufficient strength. The thickness of the substrate 40 is reduced to a desired thickness.

[First etching step]
Next, as shown in FIG. 9C, a resist 401 is applied to the other surface 40b of the substrate 40 using a spin coating method or the like, and the resist 401 is applied to the first recess 41 (see FIG. 9) using a photolithography method or the like. 7), patterning is performed according to the planar shape.
Next, as shown in FIG. 9D, the silicon substrate layer 43 is etched partway from the other surface 40b side of the substrate 40 by dry etching using the Bosch process, and the first recess 41 is formed. At this time, the etching is performed including a range overlapping with the piezoresistive element 20 in plan view.
The depth H1 of the first recess 41 is at least half the thickness t of the silicon substrate layer 43 (H1 ≧ (t / 2)).
Note that the etching here may be wet etching using an alkaline etching solution such as a KOH aqueous solution, a TMAH aqueous solution, or an EDP aqueous solution.

[Second etching step]
Next, as shown in FIG. 10E, after the resist 401 is removed, a resist 402 is formed on the other surface 40b of the substrate 40 and the first recess 41 using a CVD method or the like, and a photolithography method or the like is performed. Then, the resist 402 is patterned in accordance with the planar shape of the second recess 42 (see FIG. 7).
At this time, as a resist formation step, the mask (exposure mask) 403 is positioned with reference to the pattern provided on the one surface 40 a side of the substrate 40. Note that the piezoresistive element 20 is preferably used as the pattern.
Specifically, for example, the alignment cameras B and C recognize the piezoresistive elements 21 and 22, the alignment cameras B ′ and C ′ recognize the alignment marks 403b and 403c of the mask 403, and the alignment camera B Position alignment (positioning) between the substrate 40 and the mask 403 is performed so that a predetermined positional relationship is established between −B ′ and the alignment camera CC ′.

Next, as shown in FIG. 10 (f), the bottom of the first recess 41 is etched until it reaches the SiO ₂ layer 44 by dry etching using the Bosch process, thereby forming the second recess 42. At this time, the etching is performed so as to include at least part (here, all) of the range overlapping with the piezoresistive element 20 in plan view.
As a result, the diaphragm 10 is formed at the bottom of the second recess 42. In other words, the second recess 42 having the diaphragm 10 at the bottom is formed.
At this time, the depth H2 of the second recess 42 is equal to or less than the depth H1 of the first recess 41 (H2 ≦ H1).
Next, as shown in FIG. 10G, the resist 402 is stripped using a stripping agent or the like.

[Pressure reference chamber formation process]
Next, as shown in FIG. 10H, a base substrate 60 made of a glass plate, a silicon substrate, or the like is attached to the other surface 40b side of the substrate 40 in a vacuum (for example, a degree of vacuum of 10 Pa or less). The pressure reference chamber S is formed by bonding using the bonding member.
If glass containing alkali metal ions (movable ions) (for example, borosilicate glass such as Pyrex (registered trademark)) is used for the base substrate 60, the base substrate 60 and the substrate 40 (silicon substrate layer 43) are bonded to each other. Bonding can be performed using an anodic bonding method.
The pressure reference chamber S may not be in a vacuum state, and may be in an atmospheric pressure state filled with an inert gas such as nitrogen, argon, or helium.
Through the above steps, the pressure sensor 2 shown in FIG. 7 is obtained.

As described above, the manufacturing method of the pressure sensor 2 according to the second embodiment is based on the pattern provided on the one surface 40a side of the same substrate 40 as the piezoresistive element 20 in the second etching step. A resist forming step of positioning 403;
From this, the manufacturing method of the pressure sensor 2 improves the patterning accuracy of the resist 402 with respect to the piezoresistive element 20 as compared with the case where the pattern provided on the other surface 40b side of the substrate 40 is used as a reference. The recess 42 can be formed with high accuracy.
As a result, the manufacturing method of the pressure sensor 2 can further reduce the displacement of the relative position between the piezoresistive element 20 and the outline of the diaphragm 10.

Further, in the manufacturing method of the pressure sensor 2, when the pattern is the piezoresistive element 20, since the pattern and the piezoresistive element 20 are the same, the displacement of the relative position between the pattern and the piezoresistive element 20 is “ 0 ”, and the mask 403 can be positioned more accurately in the resist formation step.
As a result, the manufacturing method of the pressure sensor 2 can further reduce the displacement of the relative position between the piezoresistive element 20 and the outline of the diaphragm 10.

The pressure sensor 2 is provided with a through-hole 61 communicating with the pressure reference chamber S in the base substrate 60 as shown in a schematic cross-sectional view showing a schematic configuration of a pressure sensor according to a modification of the second embodiment in FIG. The reference chamber S may be configured to communicate with the outside.
According to this, the pressure sensor 2 has a pressure (white arrow) applied to the one surface 40a side of the substrate 40 and the other surface 40b side separated (isolated) from the one surface 40a side by a partition (not shown). It functions as a differential pressure sensor that detects the difference from the pressure applied to (black arrow).
In this case, the pressure reference chamber forming step may be performed in the atmosphere.

  Note that the physical quantity sensor is not limited to the pressure sensor, and can be applied to a load sensor, an acceleration sensor, an angular velocity sensor, and the like.

DESCRIPTION OF SYMBOLS 1, 2 ... Pressure sensor as physical quantity sensor, 10 ... Diaphragm, 11, 12, 13, 14 ... Edge of diaphragm outline, 20, 21, 22, 23, 24 ... Piezoresistive element as strain detection element, 30 ... detection circuit, 31 ... connecting unit, 40 ... substrate, 40a ... one surface, 40b ... other surface, 41 ... first concave portion, 42 ... second concave portion, 43 ... silicon substrate layer, 44 ... SiO ₂ layer 45 ... Silicon layer 46 ... Insulating film 50 ... Cavity layer 51 ... Oxide film layer 51 '... Sacrificial layer 52 ... Metal layer 53 ... Through hole 54 ... Sealing layer 60 ... Base substrate 61 ... Through hole, 401, 402 ... resist, 403 ... mask, 403b, 403c ... alignment mark, S ... pressure reference chamber.

Claims (6)

Preparing a substrate on one surface side on which a strain detection element that receives a strain and outputs a signal is disposed;
Etching the substrate including a range overlapping the strain detection element in plan view from the other surface side that is in a front-back relationship with the one surface, and forming a first recess;
A second etching step of dry-etching the bottom of the first recess including at least a part of a range overlapping the strain detection element in plan view, and forming a second recess having a diaphragm on the bottom;
The depth of the 2nd crevice is below the depth of the 1st crevice, The manufacturing method of the physical quantity sensor characterized by the above-mentioned.   2. The physical quantity sensor according to claim 1, wherein the second etching step includes a resist formation step of positioning a mask with reference to a pattern provided on the one surface side of the substrate. Production method.   The method of manufacturing a physical quantity sensor according to claim 2, wherein the pattern is the strain detection element.   The method of manufacturing a physical quantity sensor according to any one of claims 1 to 3, further comprising a step of reducing the thickness of the substrate before the first etching step.   5. The method according to claim 1, further comprising a step of forming a pressure reference chamber that overlaps the diaphragm in a plan view on the one surface side of the substrate before the first etching step. A method for producing a physical quantity sensor according to claim 1.   The method of manufacturing a physical quantity sensor according to claim 1, wherein the physical quantity sensor is a pressure sensor having a pressure detection function.

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