JP4965274B2 - Pressure sensor - Google Patents

Description

  The present invention relates to a pressure sensor, and more particularly to a semiconductor pressure sensor.

In the conventional pressure sensor, a concave portion is formed on the back surface of the substrate, and the bottom surface of the concave portion is a pressure strain portion. In addition, a strain gauge is formed on the surface of the substrate that is above the pressure strain portion. When the pressure strain portion is deformed, the amount of deformation is detected as a resistance change of the strain gauge, and the amount of strain is measured. As a method for forming the recess, wet etching or dry etching is known. When silicon is etched with an alkaline solution using a (100) crystal orientation substrate, it is etched into a tapered shape. The taper angle is an angle determined by the crystal orientation, and a taper angle of approximately 54 degrees is formed. The substrate thickness to be used is generally several hundred μm or more because of substrate handling limitations. The thickness of the substrate and the taper angle increase the size of the entire device, which is a barrier to downsizing the sensor. Since this tapered shape is not preferable in order to realize a reduction in the size of the sensor, a method using wet etching with an alkaline solution using a silicon substrate having a (110) crystal orientation is known. As another method, a method is known in which a recess having a substantially vertical wall is formed by dry etching using plasma so as not to depend on the crystal direction of silicon (see, for example, Patent Document 1).
JP 2006-3100 A

  However, when the inventor processes the concave portion substantially vertically to reduce the size of the sensor, the mechanical strength of the pressure strain portion is significantly reduced, and the pressure strain portion is damaged and destroyed only by applying a small pressure. I found. Furthermore, it has been found that when an SOI substrate (Silicon On Insulator) made of single crystal silicon / silicon oxide / single crystal silicon is used as the substrate, the mechanical strength is further reduced significantly. As a result of intensive studies by the inventors, it has been found that the patterned shape of the conductive film and insulating film formed on the sensor surface has an effect. That is, it has been found that there is film stress due to the difference in thermal expansion coefficient from the silicon substrate on the patterned conductive film and insulating film end faces, and this stress reduces the fracture resistance of the silicon substrate. On the other hand, the inventor has found that by optimizing the formation region of the conductive film and the insulating film, damage and destruction of the pressure strain portion can be greatly reduced, and the present invention has been completed.

  That is, according to the present invention, in the compact pressure sensor in which the side wall of the concave portion in which the pressure straining portion is formed is formed substantially vertically, the fracture resistance of the pressure straining portion (diaphragm) is greatly reduced while realizing the downsizing of the sensor element. An object is to provide an improved pressure sensor.

The present invention is provided in a single crystal silicon substrate, a recess formed by etching the single crystal silicon substrate from the bottom surface, a pressure strain portion exposed on the bottom surface of the recess, and an active layer above the pressure strain portion. A pressure sensor that detects a pressure applied to the pressure strain portion as a change in resistance of the strain gauge, the active layer including a strain gauge and a conductive layer formed on the active layer with an insulating film interposed therebetween, along the <110> direction, on the line from the rotation center of the pressure strain generating portion, the step D of the distance S and the conductive film from the edge of the pressure strain generating portion to the edge portion of the conductive film, S / The pressure sensor satisfies the relationship of D ≧ 80.

The present invention also includes an SOI substrate on which an active layer made of a support substrate, an insulating layer, and single crystal silicon is laminated, a recess formed by etching the support substrate from the bottom surface, and a pressure source exposed on the bottom surface of the recess. Including a strained portion, a strain gauge provided in an active layer above the pressure straining portion, and a conductive layer formed on the active layer with an insulating film sandwiched between them, and applying pressure applied to the pressure straining portion. a pressure sensor for detecting a change in resistance of the strain gauges, the active layer <110> along the direction, on the line from the rotation center of the pressure strain generating portion, from the edge of the pressure strain generating portion of the conductive film The pressure sensor is characterized in that the distance S to the edge and the step D of the conductive film satisfy the relationship of S / D ≧ 80.

  As described above, in the pressure sensor according to the present invention, it is possible to reduce the size of the sensor element while improving the strength of the diaphragm.

Embodiment 1. FIG.
FIG. 1 is a cross-sectional view of a pressure sensor according to a first embodiment of the present invention, indicated as a whole by 100, and is a cross-sectional view when FIG. 2 described later is viewed in the <110> direction.

The pressure sensor 100 is made of a silicon substrate 1. An n-type diffusion wiring 2 and an n-type strain gauge 3 are formed on the silicon substrate 1. The diffusion wiring 2 and the strain gauge 3 are formed by an impurity diffusion method or an ion implantation method. The impurity concentration of the diffusion wiring 2 is about 1 × 10 ¹⁸ to 1 × 10 ²⁰ atoms / cm ³ , and the impurity concentration of the strain gauge 3 is about 1 × 10 ¹⁷ to 1 × 10 ¹⁸ atoms / cm ³ . The diffusion wiring 2 serves to electrically connect the strain gauge 3 and the wiring layer 7.

  As the strain gauge 3, a metal film such as Ni—Cr or a p-type region formed in the silicon substrate 1 made of n-type silicon can also be used. When the p-type region is used, in order to electrically isolate the p-type region from the n-type silicon substrate 1, the pn junction region needs to be in a reverse bias state.

  A recess 18 is provided on the other surface of the silicon substrate 1, and the bottom surface of the recess serves as the pressure strain portion 8. In order to realize element miniaturization, at least one side wall surface of the recess 18 is processed substantially vertically.

  On the silicon substrate 1 on which the strain gauge 3 is formed, a first insulating film 4 made of, for example, silicon oxide is formed. Further, a conductive film 5 is formed on the first insulating film 4. The conductive film 5 serves as a shield for increasing the electrostatic resistance of the strain gauge 3. As a shield, a polycrystalline silicon film containing an impurity such as phosphorus has a thermal expansion coefficient close to that of a silicon substrate made of single crystal silicon, so that it is desirable in consideration of output temperature characteristics from a strain gauge. The first insulating film 4 electrically insulates the diffusion wiring 2, the strain gauge 3 and the conductive film 5.

On the conductive film 5, a second insulating film 6 made of, for example, silicon oxide is formed.
The first insulating film 4 and the second insulating film 6 are provided with a first via 22 and a second via, and a wiring layer made of, for example, aluminum is provided so as to fill them. The wiring layer 7 is connected to a pad portion (not shown) and outputs a signal to the outside by wire bonding or solder bump bonding.

  The conductive film 5 is kept at a constant power supply potential so that a noise signal does not enter the strain gauge from the outside. The pressure sensor is connected to a power source through the wiring layer 7. The conductive film 5 has been confirmed to exhibit a shielding effect even at a floating potential, but when a large amount of negative charge is incident on the surface of the pressure sensor, the conductive film 5 is connected to the power supply potential. This is desirable because it can quickly remove negative charges.

  In the pressure sensor, the pressure straining portion is distorted by the pressure applied to the pressure straining portion 8, and the amount of strain is detected as a resistance change of the strain gauge 3. For example, an absolute pressure applied to the pressure sensor is measured by anodically bonding a glass substrate (not shown) to the silicon substrate surface on which the recesses 18 are formed, and holding the recesses 18 below the pressure-distortion units in a vacuum. It becomes an absolute pressure sensor. Moreover, when a glass substrate is not provided as shown in FIG. 1, it becomes a differential pressure sensor which can measure the differential pressure of both sides (the upper part and the lower part of a pressure sensor) of a pressure strain part.

  In the present embodiment, the region where the conductive film and the insulating film are formed is adjusted with respect to the pressure strain portion 8, the change in the fracture strength of the diaphragm is measured, and the experimental results shown in FIG. 3 are obtained. From the results of FIG. 3, the inventor has found that the conductive film and the positional relationship between the conductive film formation region and the pressure strain portion 8 greatly affect the fracture resistance of the diaphragm (pressure strain portion).

  FIG. 2A shows the positional relationship between the pressure strain portion 8 and the conductive film 5 formed thereabove when the pressure sensor is viewed from above, and FIG. Represents the figure. In order to facilitate understanding, the second insulating film and the like are omitted.

  Here, when a single crystal substrate having a main surface of (100) crystal orientation is used as the silicon substrate, as shown in FIG. 2A, the vertical direction and the horizontal direction of the paper surface are <110> directions. The pressure strain portion formed on the silicon substrate 1 has a rectangular shape in which each side is formed along the <110> direction. In FIG. 2, the rotation center of the pressure straining portion 8 is represented by O. Here, the rotation center O refers to a position that is the same as the original shape even if the pressure strain portion 8 is rotated 180 degrees around the rotation center O.

  In addition, on the straight extension line from the rotation center O toward the edge of the pressure straining portion 8 in the <110> direction when viewed from the vertical direction with respect to the surface of the silicon substrate 1, the pressure straining portion 8. Let S be the distance from the edge of the film to the edge of the conductive film 5. In FIG. 3, when the edge portion of the conductive film 5 is on the inner side (rotation center O side) than the edge portion of the pressure strain portion 8, the − (minus) sign is attached. A step at the edge of the conductive film is denoted by D.

  Note that the strain gauge 3 is formed so as to cover the upper portion of the pressure strain portion 8 in order to improve the detection sensitivity of the strain amount.

  In FIG. 3, the horizontal axis represents the ratio (S / D) between the distance S and the step D, and the vertical axis represents the fracture strength of the diaphragm (pressure strain portion 8). As can be seen from FIG. 3, by setting the absolute value of S / D to about 80 or more, the fracture strength is greatly improved and can be improved by about 3 times. More preferably, the S / D value is 100 or more and 1300 or less. Even if S / D is 1300 or more, there is an effect in terms of improving the mechanical strength, but in terms of device miniaturization, differentiation from tapered etching becomes small.

  For example, when the level difference D is 0.3 μm, the distance S from the edge of the pressure strain portion 8 to the edge of the conductive film 5 along the <110> direction may be 24 μm or more, and more preferably. Is 30 μm or more and 390 μm or less.

  Further, in order for the conductive film 5 to have a shielding effect, it is necessary to form the conductive film 5 so as to cover the strain gauge 3.

  By satisfying the above conditions and setting the relationship between S and D in this way, the fracture resistance of the pressure straining portion 8 can be greatly improved, and the device can be downsized.

  As can be seen from FIG. 2, there are two <110> directions in the active layer 13 made of single crystal silicon whose main surface is the (100) plane. In such a case, the S / D needs to be 80 or more in both cases.

  When the main surface of the silicon substrate 1 is the (110) plane, the S / D needs to be 80 or more in the <110> direction along the plane of the silicon substrate in order to improve the breakdown voltage. It becomes. For example, when viewed from the vertical direction with respect to the surface of the silicon substrate, on the extension line of the straight line from the rotation center O toward the edge of the pressure strain portion in the <110> direction, from the edge of the pressure strain portion Let S be the distance to the edge of the insulating film. Further, D is a step at the edge of the insulating film. By setting the absolute value of S / D to about 80 or more, the fracture strength of the pressure strain portion is greatly improved.

  Furthermore, it has been experimentally confirmed that the relationship as shown in FIG. 3 is established even if the shape of the pressure strain portion is circular, substantially circular, polygonal, or ring-shaped.

  Although the case where the film level difference is the conductive film 5 has been described, the same effect can be obtained even in an insulating film which is a material different from single crystal silicon, or in an end portion of another conductive film 5, for example, the wiring layer 7.

  FIG. 4 shows another pressure sensor according to the present embodiment, indicated as a whole by 200, in which the pressure straining portion 8 is formed in a ring shape. 4A is a top view (the second insulating film 6 and the like are omitted as in FIG. 2), and FIG. 4B is a cross-sectional view when FIG. 4A is viewed in the AA direction. is there. 4, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

  Also in the pressure sensor 200, S / D is 80 or more, more preferably S / D is 100 between the film level difference D and the distance S between the edge of the pressure strain portion 8 and the edge of the shield film 5. Thus, the relationship of 1300 or less is established.

  In addition, as shown in FIG. 4A, the conductive film may not be formed symmetrically with respect to the rotation center O. Even in such a case, the S / D relationship in the <110> direction is the above relationship. If you have.

  The reason why the effect of the present invention can be obtained is considered that the stress distribution at the film end affects the diaphragm and determines the fracture strength of the pressure strain portion. Since single crystal silicon has the property of being easily broken in the <110> direction, it is considered that the fracture strength can be improved by setting the S / L within a predetermined range with respect to the <110> direction.

  Next, a manufacturing method of the pressure sensor 100 according to the present embodiment will be described with reference to FIG. The manufacturing method of the pressure sensor 100 includes the following steps 1 to 5.

Step 1: As shown in FIG. 5A, a single crystal silicon substrate 1 is prepared.
The single crystal silicon substrate is made of n-type single crystal silicon and has a main surface of (100). The support substrate 11 is formed of single crystal silicon, but may be formed of polycrystalline silicon, sapphire, or the like.

Next, an n-type region is formed on the main surface of the single crystal silicon substrate to form a diffusion wiring and a strain gauge. For example, a thermal diffusion method or an ion implantation method is used to form the n-type region.
The performance of the strain gauge greatly depends on the impurity concentration. The impurity concentration of the strain gauge is preferably in the range of about 1 × 10 ¹⁷ to about 1 × 10 ¹⁸ atoms / cm ³ . Further, the impurity concentration of the diffusion wiring is preferably high in order to reduce the resistance, and is preferably in the range of about 1 × 10 ¹⁸ to about 1 × 10 ²⁰ atoms / cm ³ .

  Step 2: As shown in FIG. 5B, a first insulating film is formed so as to cover the upper surface of the main surface of the silicon substrate on which the strain gauge is formed. The first insulating film is made of, for example, silicon oxide and is formed using a CVD method or the like.

  Subsequently, a shield film is formed. The shield film is formed by, for example, forming a polycrystalline silicon film on the entire surface by using the CVD method and then processing it into a desired shape by using a photoengraving technique and reactive plasma etching. In order to improve the conductivity of the polycrystalline silicon film, it is preferable to introduce an impurity such as phosphorus.

  Step 3: As shown in FIG. 5C, a second insulating film is formed on the entire surface. The second insulating film is made of, for example, silicon oxide and is formed using a CVD method.

  Next, the first via 21 and the second via are formed in the second insulating film and the first insulating film by using photolithography and reactive ion etching. The first via is formed so as to reach the shield film, and the second via is formed so as to reach the diffusion wiring.

Next, for example, an aluminum layer is formed on the entire surface by sputtering or vapor deposition, for example, and then patterned into a desired shape using a photoengraving technique to form a wiring layer. The wiring layer is connected to the diffusion wiring and the shield film, and further connected to a power source (not shown). As a result, the potential of the shield film becomes the power supply potential.
Note that the surface may be covered with a protective film after the wiring layer is formed. The protective film is made of, for example, silicon nitride.

Step 4: As shown in FIG. 5 (d), the silicon substrate is etched from the surface opposite to the main surface to form the concave portion 18, and the region exposed on the bottom surface of the concave portion 18 is defined as the pressure strain portion 8. As the etching of the support substrate, reactive plasma etching using SF ₆ gas is used. The etching depth is determined according to the pressure at which the pressure sensor 100 is used. By adjusting the plasma etching conditions, for example, the high-frequency power applied to the substrate, the side wall can be dug approximately vertically. When the silicon substrate has a (110) crystal plane as the main surface, one or more sidewalls can be dug approximately vertically even by etching using an alkaline solution such as KOH.

  Process 5: As shown in FIG.5 (e), when using as an absolute pressure sensor, the glass substrate 10 is anodically bonded to the surface which etched, and the inside of a recessed part is made into a vacuum state. Moreover, when using as a differential pressure sensor, the glass substrate 10 is not necessarily required.

  Finally, a pad portion (not shown) connected to the wiring layer 7 is connected to the outside using solder bumps or wire bonds. The pressure sensor 100 according to the present embodiment is completed through the above steps.

Embodiment 2. FIG.
FIG. 6 is a cross-sectional view of the pressure sensor according to the second exemplary embodiment of the present invention, the whole being represented by 300, and is a cross-sectional view when FIG. 7 described later is viewed in the <110> direction.
The pressure sensor 300 includes an SOI (Silicon On Insulator) substrate 14 including a support substrate 11, a buried oxide film (insulating layer) 12, and an active layer 13. In the SOI substrate 14, for example, the support substrate 11 and the active layer 13 are made of silicon, and the buried oxide film 12 is made of silicon oxide. Furthermore, the active layer 13 is formed of single crystal silicon, while the support substrate 11 may be formed of polycrystalline silicon or sapphire in addition to the single crystal silicon substrate.

In the active layer 13, an n-type diffusion wiring 2 and an n-type strain gauge 3 are formed. The diffusion wiring 2 and the strain gauge 3 are formed by an impurity diffusion method or an ion implantation method. The impurity concentration of the diffusion wiring 2 is about 1 × 10 ¹⁸ to 1 × 10 ²⁰ atoms / cm ³ , and the impurity concentration of the strain gauge 3 is about 1 × 10 ¹⁷ to 1 × 10 ¹⁸ atoms / cm ³ . The diffusion wiring 2 serves to electrically connect the strain gauge 3 and the wiring layer 7.

  As the strain gauge 3, a metal film such as Ni—Cr or a p-type region formed in the active layer 13 made of n-type silicon can also be used. When the p-type region is used, the pn junction region needs to be in a reverse bias state in order to electrically isolate the p-type region from the n-type active layer 13.

  The support substrate 11 is provided with a recess so that the buried oxide film 12 is exposed, and the bottom surface of the recess serves as the pressure strain portion 8. In the pressure sensor 300, the buried oxide film 12 remains on the bottom surface of the recess, but the buried oxide film 12 can be further thinned or removed to expose the active layer 13. In some cases, the support substrate 11 having a predetermined film thickness is left.

A first insulating film 4 made of, for example, silicon oxide is formed on the active layer 13. Further, a conductive film 5 is formed on the first insulating film 4. The conductive film 5 is made of polycrystalline silicon, aluminum, or the like containing impurities such as phosphorus. Since polycrystalline silicon has a thermal expansion coefficient close to that of the active layer 13 made of single crystal silicon, it is desirable to use polycrystalline silicon in consideration of temperature characteristics. The first insulating film 4 electrically insulates the diffusion wiring 2, the strain gauge 3 and the conductive film 5.
On the conductive film 5, a second insulating film 6 made of, for example, silicon oxide is formed.

  The first insulating film 4 and the second insulating film 6 are provided with a first via 21 and a second via 22, and a wiring layer 7 made of, for example, aluminum is provided so as to fill them. The wiring layer 7 is connected to a pad portion (not shown) and outputs a signal to the outside by wire bonding or solder bump bonding.

  The conductive film 5 is kept at a constant power supply potential so that a noise signal does not enter the strain gauge 3 from the outside. The pressure sensor 300 is connected to a power source via the wiring layer 7. Although the shield film 5 has been confirmed to exhibit a shielding effect even at a floating potential, when a large amount of negative charge is incident on the surface of the pressure sensor 300, the conductive film 5 is connected to the power supply potential. It is desirable that the negative charge can be quickly removed.

  In the pressure sensor 300, the pressure strain unit 8 is distorted by the pressure applied to the pressure strain unit 8, and the amount of strain is detected as a resistance change of the strain gauge 3.

  For example, an absolute pressure sensor that measures the absolute pressure applied to the pressure sensor 300 by anodically bonding a glass substrate (not shown) to the bottom surface of the support substrate 11 and holding the concave portion below the pressure strain portion 8 in a vacuum. It becomes. Moreover, when a glass substrate is not provided as shown in FIG. 6, it becomes a differential pressure sensor which can measure the differential pressure of both sides (the upper part and the lower part of the pressure sensor 300) of the pressure strain part 8. FIG.

  In the present embodiment, the region where the conductive film 5 is formed is adjusted with respect to the pressure strain portion 8, the change in the fracture strength of the diaphragm is measured, and the experimental results shown in FIG. 8 are obtained. From the result of FIG. 8, the inventor found that the positional relationship between the formation region of the conductive film 5 and the pressure strain portion 8 greatly affects the fracture resistance of the diaphragm (pressure strain portion 8).

FIG. 7 shows a positional relationship between the pressure strain portion 8 and the conductive film 5 formed thereabove when the pressure sensor 300 is viewed from above. In order to facilitate understanding, the second insulating film 6 and the like are omitted.
Normally, the active layer 13 is made of a (100) substrate, and as shown in FIG. 7, the vertical direction and the horizontal direction of the paper surface are the <110> directions. Further, the pressure strain portion 8 (the bottom surface of the recess formed in the support substrate 11) formed on the support substrate 11 has a rectangular shape in which each side is formed along the <110> direction. In FIG. 2, the rotation center of the pressure straining portion 8 is represented by O. Here, the rotation center O refers to a position that is the same as the original shape even if the pressure strain portion 8 is rotated 180 degrees around the rotation center O.

  Further, the distance from the edge of the pressure strain portion 8 to the edge of the conductive film 5 on the extension line from the rotation center O in the <110> direction when viewed from the vertical direction with respect to the surface of the active layer 13. Is S, and the film step at the edge is D. In FIG. 8, when the step of the conductive film 5 is on the inner side (rotation center O side) than the edge of the pressure strain portion 8, it is indicated with a − (minus) sign.

  Note that the strain gauge 3 is formed so as to cover the upper portion of the pressure strain portion 8 in order to improve the detection sensitivity of the strain amount.

  FIG. 8 shows the ratio (S / D) between the distance S and the step D on the horizontal axis, and the fracture strength of the diaphragm (pressure strain portion 8) on the vertical axis. As can be seen from FIG. 8, by setting the absolute value of S / D to 80 or more, the fracture strength is greatly improved, and can be about 5 in the case of 80 or less. Preferably, the value of S / D is 100 or more and 1300 or less.

  For example, when the step D is 0.3 μm, the distance S from the edge of the pressure straining portion 8 to the edge of the shield film 5 along the <110> direction may be 24 μm or more, preferably 30 μm or more and 390 μm or less.

  As described above, in order for the conductive film 5 to have a shielding effect, it is necessary to form the conductive film 5 so as to cover the upper side of the strain gauge 3. By setting the relationship in this way, it is possible to achieve element miniaturization and obtain a noise-free pressure measurement result while greatly improving the fracture resistance of the pressure straining portion 8.

  As can be seen from FIG. 7, there are two <110> directions in the active layer 13 made of single crystal silicon whose main surface is the (100) plane. In such a case, the S / L must be 0.1 or more in both cases.

  When the main surface of the active layer 13 is the (110) plane, the S / D needs to be 80 or more in the <110> direction along the surface of the active layer in order to improve the breakdown voltage. It becomes.

  Further, it has been experimentally confirmed that the relationship shown in FIG. 8 is established even when the shape of the pressure straining portion 8 is circular, substantially circular, polygonal, or ring-shaped.

  Note that although the case where the film step is made of a conductive film has been described, the same effect can be obtained even in an insulating film that is a different material from single crystal silicon, or in another conductive film such as an end portion of a wiring layer.

  FIG. 9 shows another pressure sensor according to the present embodiment, indicated as a whole by 400, in which the pressure straining portion 8 is formed in a ring shape. 9A is a top view (similar to FIG. 2, the second insulating film 6 and the like are omitted), and FIG. 9B is a cross-sectional view when FIG. 9A is viewed in the BB direction. is there. 9, the same reference numerals as those in FIG. 6 denote the same or corresponding parts.

  Also in the pressure sensor 400, the distance S between the rotation center O and the edge of the pressure strain portion 8 and the distance S between the edge of the pressure strain portion 8 and the edge of the shield film 5 is S / The relationship D is 80 or more, preferably S / D is 100 or more and 1300 or less.

  As shown in FIG. 9A, the conductive film 5 may not be formed symmetrically with respect to the rotation center O. Even in such a case, the S / D is the above in the <110> direction. It only has to have a relationship.

  Although the reason why the effect of the present invention can be obtained is not necessarily clear, the stress distribution of the edge of the conductive film 5 and the stress distribution of the SOI substrate 14 influence each other to determine the fracture strength of the pressure strain portion 8. It is thought that. In addition, since the single crystal silicon substrate whose main surface is (100) plane has a characteristic of being easily cracked in the <110> direction, the fracture strength can be reduced by setting the S / D within a predetermined range with respect to the <110> direction. Can be improved.

  Next, a manufacturing method of the pressure sensor 300 according to the present embodiment will be described with reference to FIG. The manufacturing method of the pressure sensor 300 includes the following steps 1 to 5.

Step 1: As shown in FIG. 10A, an SOI substrate 1 is prepared in which a support substrate 11 made of silicon, a buried oxide film 12 made of silicon oxide, and an active layer 13 made of silicon are sequentially laminated.
The active layer 13 is made of n-type single crystal silicon and has a main surface of (100). The support substrate 11 is formed of single crystal silicon, but may be formed of polycrystalline silicon, sapphire, or the like.

  Next, an n-type region is formed in the active layer 13 of the SOI substrate 1 to form the diffusion wiring 2 and the strain gauge 3. For example, a thermal diffusion method or an ion implantation method is used to form the n-type region.

The performance of the strain gauge 3 greatly depends on the impurity concentration. The impurity concentration of the strain gauge 3 is preferably in the range of about 1 × 10 ¹⁷ to about 1 × 10 ¹⁸ atoms / cm ³ .

Further, the impurity concentration of the diffusion wiring 2 is preferably high in order to reduce the resistance, and is preferably in the range of about 1 × 10 ¹⁸ to about 1 × 10 ²⁰ atoms / cm ³ .

Step 2: As shown in FIG. 10B, a first insulating film 4 is formed so as to cover the upper surface of the SOI substrate 1. The first insulating film 4 is made of, for example, silicon oxide and is formed using a CVD method or the like.
Subsequently, the conductive film 5 is formed. The conductive film 5 is formed, for example, by forming a polycrystalline silicon film on the entire surface by using the CVD method and then processing it into a desired shape by using a photoengraving technique and reactive plasma etching. In order to improve the conductivity of the polycrystalline silicon film, it is preferable to introduce an impurity such as phosphorus.

  Process 3: As shown in FIG.10 (c), the 2nd insulating film 6 is formed in the whole surface. The second insulating film 6 is made of, for example, silicon oxide and is formed using a CVD method.

  Next, the first via 21 and the second via 22 are formed in the second insulating film 6 and the first insulating film 4 using photolithography and reactive ion etching. The first via 21 is formed so as to reach the shield film 5, and the second via 22 is formed so as to reach the diffusion wiring 2.

  Next, an aluminum layer is formed on the entire surface by, eg, sputtering or vapor deposition, and then patterned into a desired shape using a photoengraving technique to form the wiring layer 7. The wiring layer 7 is connected to the diffusion wiring 2 and the shield film 5 and further connected to a power source (not shown). As a result, the potential of the shield film 5 becomes the power supply potential.

  Note that after the wiring layer 7 is formed, the surface may be covered with a protective film. The protective film is made of, for example, silicon nitride.

Process 4: As shown in FIG.10 (d), the support substrate 11 is etched from a bottom face, a recessed part is formed, and the area | region exposed to the bottom face of the recessed part is made into the pressure strain part 8. FIG. For example, reactive plasma etching using SF ₆ gas is used for etching the support substrate 11. The etching depth is determined according to the pressure at which the pressure sensor 300 is used. For example, the pressure-distortion portion 8 may be formed thick with some support substrate 11 left. Further, as shown in FIG. 9D, the support substrate 11 may be etched until the buried oxide film 12 is exposed. Furthermore, the buried oxide film 12 may be partially or entirely removed, or the active layer 13 may be slightly etched. When the (110) crystal plane is the main surface as the support substrate, one or more sidewalls can be dug approximately vertically by etching using an alkaline solution such as KOH.

Step 5: As shown in FIG. 10 (e), when used as an absolute pressure sensor, the glass substrate 10 is anodically bonded to the bottom surface of the support substrate 13, and the inside of the recess is evacuated. Moreover, when using as a differential pressure sensor, the glass substrate 10 is not necessarily required.
Finally, a pad portion (not shown) connected to the wiring layer 7 is connected to the outside using solder bumps or wire bonds. The pressure sensor 300 according to the present embodiment is completed through the above steps.

  In the first and second embodiments, the diffusion wiring 2 and the strain gauge 3 are formed from the n-type region, but can also be formed from the p-type region.

It is sectional drawing of the pressure sensor concerning Embodiment 1 of this invention. It is the upper side figure and sectional drawing of the pressure sensor concerning Embodiment 1 of this invention. It is the relationship between the distance S / step D and the breaking strength of the diaphragm. It is the upper side figure and sectional drawing of the other pressure sensor concerning Embodiment 1 of this invention. It is sectional drawing of the manufacturing process of the pressure sensor concerning Embodiment 1 of this invention. It is sectional drawing of the pressure sensor concerning Embodiment 2 of this invention. It is a top view of the pressure sensor concerning Embodiment 2 of the present invention. It is the relationship between the distance S / step D and the breaking strength of the diaphragm. It is the upper side figure and sectional drawing of the other pressure sensor concerning Embodiment 2 of this invention. It is sectional drawing of the manufacturing process of the pressure sensor concerning Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate, 2 Diffusion wiring, 3 Strain gauge, 4 First insulating layer, 5 Conductive film, 6 Second insulating layer, 7 Wiring layer, 8 Pressure strain part, 10 Glass substrate, 11 Support substrate, 12 Embedded insulating layer , 13, active layer, 14 SOI substrate, 18 recess 22 via, 100 pressure sensor.

Claims (8)

A single crystal silicon substrate;
A recess formed by etching the silicon substrate from the bottom surface;
A pressure strain portion exposed on the bottom surface of the recess;
A strain gauge provided in the active layer above the pressure strain portion;
A conductive layer formed on the active layer with an insulating film interposed therebetween,
A pressure sensor for detecting a pressure applied to the pressure strain portion as a resistance change of the strain gauge,
Along the <110> direction of the active layer, on the line from the rotation center of the pressure strain generating part, of the distance S and the conductive film from the edge of the pressure strain generating portion to the edge portion of the conductive film Step D is
S / D ≧ 80
A pressure sensor satisfying the relationship   2. The pressure sensor according to claim 1, wherein the main surface of the single crystal silicon substrate is a (100) plane or a (110) plane.   The pressure sensor according to claim 1, wherein the conductive film is made of polycrystalline silicon.   The pressure sensor according to claim 1, wherein the potential of the conductive film is held at a power supply potential of the pressure sensor. An SOI substrate in which an active layer made of a supporting substrate, an insulating layer, and single crystal silicon is stacked;
A recess formed by etching the support substrate from the bottom surface;
A pressure strain portion exposed on the bottom surface of the recess;
A strain gauge provided in the active layer above the pressure strain portion;
A conductive film formed on the active layer with an insulating film interposed therebetween,
A pressure sensor for detecting a pressure applied to the pressure strain portion as a resistance change of the strain gauge,
Along the <110> direction of the active layer, on the line from the rotation center of the pressure strain generating part, of the distance S and the conductive film from the edge of the pressure strain generating portion to the edge portion of the conductive film Step D is
S / D ≧ 80
A pressure sensor satisfying the relationship 6. The pressure sensor according to claim 5 , wherein the main surface of the active layer is a (100) plane or a (110) plane. The pressure sensor according to claim 5 , wherein the conductive film is made of polycrystalline silicon. 6. The pressure sensor according to claim 5 , wherein the potential of the conductive film is maintained at the power supply potential of the pressure sensor.

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