The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2009-159762, filed Jul. 6, 2009, which is incorporated herein by reference.
The present invention relates to a pressure sensor and to a pressure sensor manufacturing method, and, in particular, relates to a pressure sensor having a diaphragm, and to a method for manufacturing that pressure sensor.
Pressure sensors that use a semiconductor piezoresistance effect are small and light, and have high sensitivity, and thus are used broadly in fields such as industrial instrumentation and medicine. In a pressure sensor is set forth in Unexamined Japanese Patent Application Publication H06-102119 (“JP '119”), deformation gauges having a piezo effect and resistance portions are formed on a diaphragm of a semiconductor substrate. Additionally, an insulating layer having a contact holes is formed on the semiconductor substrate. Furthermore, connections are made, through the contact holes, between the resistance portions and electrode pads that are formed on top of the insulating layer.
However, in the pressure sensor as set forth in JP '119, it is not possible to prevent leakage current cause but insulating defects.
The present invention is to correct problem areas such as this, and the object thereof is to provide a pressure sensor, and a pressure sensor manufacturing method, able to prevent the characteristic defects caused by leakage current.
A pressure sensor as set forth in a first aspect according to the present invention is provided with a semiconductor substrate, an insulating layer, and an external conducting portion. An internal resistance portion is formed within the semiconductor substrate. Additionally, the insulating layer is formed on top of the semiconductor substrate. Additionally, the external conducting portion is formed on top of the insulating layer. Furthermore, a contact for connecting electrically between the external conducting portion and the internal resistance portion is formed in the insulating layer. Furthermore, the external conducting portion is formed in a range corresponding to the range wherein is formed the internal resistance portion on the semiconductor substrate.
In the first aspect according to the present invention, the external conducting portion is formed in a range corresponding to the range wherein is formed the internal resistance portion on the semiconductor substrate. In other words, the external conducting portion is formed on top of a range wherein the internal resistance portion is formed. Doing so means that the internal resistance portion is formed under the insulating defect when there is an insulating defect, such as a flaw in the insulating layer, that is positioned under the external conducting portion. Furthermore, because, ideally, the external conducting portion and the internal resistance portion are at the same electropotential, even if there is this insulating defect portion in the insulating layer, still there will be essentially no leakage current produced through the insulating defect portion. Additionally, even if a leakage current were produced through the insulating defect portion, it would only be an electric current from the external conducting portion to the internal resistance portion that are already connected electrically through the contact. Because of this, there would be no impact on the characteristics of the pressure sensor. Consequently, this is able to prevent characteristic defects caused by the leakage current.
A pressure sensor as set forth in a second aspect according to the present invention is provided with a semiconductor substrate, an insulating layer, and an external conducting portion. A plurality of internal resistance portions is formed within the semiconductor substrate. Additionally, the insulating layer is formed on top of the semiconductor substrate. Additionally, a plurality of external conducting portions is formed on top of the insulating layer. Furthermore, a plurality of contacts for connecting electrically between the external conducting portion and the internal resistance portion is formed in the insulating layer. Furthermore, the external conducting portion is formed in a range corresponding to the range wherein is formed the internal resistance portion on the semiconductor substrate.
The second aspect according to the present invention produces the same effect as the first aspect.
Additionally, preferably the semiconductor substrate is an n-type semiconductor substrate, where the internal resistance portions are made from p-type semiconductors, where a voltage is applied so that those parts of the semiconductor substrate that are not formed into the internal resistance portions will be at the same electropotential or higher than that of the external conducting portions, and so that the potential difference formed between the internal resistance portions of the semiconductor substrate and those parts of the semiconductor substrate that are not formed into the internal resistance portions will be less than the breakdown voltage.
Additionally, preferably the semiconductor substrate is a p-type semiconductor substrate, where the internal resistance portions are made from n-type semiconductors, where a voltage is applied so that those parts of the semiconductor substrate that are not formed into the internal resistance portions will be at the same electropotential or lower than that of the external conducting portions, and so that the potential difference formed between the internal resistance portions of the semiconductor substrate and those parts of the semiconductor substrate that are not formed into the internal resistance portions will be less than the breakdown voltage.
Doing so makes it possible to suppress to a trivial amount the current from the external conducting portions to the portions of the semiconductor substrate that are not formed into the internal resistance portions. Consequently, this is able to prevent more effectively the characteristic defects in the pressure sensor.
Furthermore, the number of contacts that are provided in the insulating layer is preferably equal to the number of external conducting portions or less than the number of external conducting portions.
If the number of contacts is high, then, structurally, there will be a greater likelihood to be affected by stresses other than pressure. The present invention suppresses the number of contacts to the minimum requirement, making it possible to reduce the effects of stresses other than pressure.
A pressure sensor manufacturing method as set forth in a third aspect according to the present invention is provided with an internal resistance portion forming process, an insulating layer forming process, an external conducting portion forming process, and a contact forming process. In the internal resistance portion forming process, the internal resistance portions are formed in the semiconductor substrate. Additionally, in the insulating layer forming process, the insulating layer is formed on top of the semiconductor substrate. In the external conducting portion forming process, the external conducting portions are formed on top of the insulating layer. Furthermore, in the contact forming process, the contacts for connecting electrically between the external conducting portion and the internal resistance portion are formed in the insulating layer. Furthermore, in the external conducting portion forming process, the external conducting portions are formed in ranges corresponding to the ranges wherein are formed the internal resistance portions on the semiconductor substrate.
In the third aspect according to the present invention, the external conducting portion is formed in a range corresponding to the range wherein is formed the internal resistance portion on the semiconductor substrate. In other words, the external conducting portion is formed on top of a range wherein the internal resistance portion is formed. Doing so means that the internal resistance portion is formed under the insulating defect when there is an insulating defect, such as a flaw in the insulating layer, that is positioned under the external conducting portion. Furthermore, because, ideally, the external conducting portion and the internal resistance portion are at the same electropotential, even if there is this insulating defect portion in the insulating layer, still there will be essentially no leakage current produced through the insulating defect portion. Additionally, even if a leakage current were produced through the insulating defect portion, it would only be an electric current from the external conducting portion to the internal resistance portion that are already connected electrically through the contact. Because of this, there would be no impact on the characteristics of the pressure sensor. Consequently, this is able to prevent characteristic defects caused by the leakage current.
Furthermore, preferably in the contact forming process, the number of contacts that are formed in the insulating layer is preferably equal to the number of external conducting portions or less than the number of external conducting portions.
If the number of contacts is high, then, structurally, there will be a greater likelihood to be affected by stresses other than pressure. The present invention suppresses the number of contacts to the minimum requirement, making it possible to reduce the effects of stresses other than pressure.
The present invention is able to prevent characteristic defects caused by the leakage current.
A form of embodiment according to the present invention will be explained below in reference to the drawings.
In the below, a specific form of embodiment wherein the present invention is applied will be explained in detail while referencing the drawings.
The pressure sensor 100 has a sensor chip 10 that is made out of a semiconductor substrate. The sensor chip 10 is a square shape. As illustrated in
As illustrated in
The differential pressure diaphragm 4, for detecting a differential pressure, is disposed in the center part of the sensor chip 10. As illustrated in
Differential pressure gauges 5A through 5D are disposed on the surface of the p-type differential pressure diaphragm 4. These four differential pressure gauges 5A through 5D are referred to, in aggregate, as the differential pressure gauges 5. The differential pressure gauges 5 are disposed at the edge portions of the differential pressure diaphragm 4. Here a single differential pressure gauge 5 is disposed near the center of each edge of the square differential pressure diaphragm 4. A differential pressure gauge 5 is disposed in the center of each edge of the differential pressure diaphragm 4. Consequently, the differential pressure gauge 5A is disposed between the center of the differential pressure diaphragm 4 and the corner A. The differential pressure gauge 5B is disposed between the center of the differential pressure diaphragm 4 and the corner B, the differential pressure gauge 5 C is disposed between the center of the differential pressure diaphragm 4 and the corner C, and the differential pressure gauge 5D is disposed between the center of the differential pressure diaphragm 4 and the corner D. The differential pressure gauge 5A and the differential pressure gauge 5B face each other with the center of the sensor chip 10 therebetween. The differential pressure gauge 5C and the differential pressure gauge 5D facing each other with the center of the sensor chip 10 therebetween.
The differential pressure gauges 5 are strain gauges having the piezoresistance effect. Consequently, when the sensor chip 10 deforms, the resistances of each of the differential pressure gauges 5A through 5D will change. Note that, on the top surface of the sensor chip, p-type diffused resistance interconnections 6A through 6D are formed connecting the individual differential pressure gauges 5A through 5D. For example, as illustrated in
The four differential pressure gauges 5A through 5D are disposed in parallel with each other. That is, the lengthwise directions of the four differential pressure gauges 5A through 5D are disposed along the diagonal line AB. Additionally, diffused resistance interconnections 6A through 6D are connected to both ends of the differential pressure gauges 5A through 5D in the lengthwise direction. The differential pressure gauges 5 are formed in the parallel to the <110> crystal axial direction wherein the piezoresistance factor is maximized in the (100) crystal face orientation of the sensor chip 10. Note that the pressure sensor 100 bridge circuit pattern in the present invention is not limited to that which is illustrated in
Additionally, as illustrated in
Additionally, the differential pressure gauges 5A through 5D and the diffused resistance interconnections 6A through 6D that form the bridge circuit are covered by the insulating layer (the oxide layer) 7, as illustrated in
Additionally, in the specific position of each individual diffused resistance interconnection 6A through 6D of the bridge circuit that is formed through the combination of the differential pressure gauges 5 and the diffused resistance interconnections 6, the contact 9 A through 9D that is formed is formed passing through a portion of the insulating layer 7. Note that in the case of the present form of embodiment, two contacts 9 are formed for applying electric power to the bridge circuit, and two contacts 9 are formed for extracting the outputs from the bridge circuit. Consequently, the number of contacts 9 is no more than the number of the differential pressure bridge gauges.
The structure of the pressure sensor 100 according to the present form of embodiment will be explained next in reference to
Here the external conducting portions 8 are electrode pads, metal interconnections, or the like.
As illustrated in
Additionally, the insulating layer 7 is formed on top of the second semiconductor layer 3. Additionally, the external conducting portions 8 are formed on top the insulating layer 7. Furthermore, contacts 9 for connecting electrically between the external conducting portions 8 and the internal resistance portions 6 are formed in the insulating layer 7. Furthermore, the number of contacts 9 that are formed in the insulating layer 7 is equal to the number of external conducting portions 8 that are formed on top of the insulating layer 7. Note that, the number of contacts 9 that are formed in the insulating layer 7 may be less than the number of external conducting portions 8 that are formed on top of the insulating layer 7.
Additionally, the external conducting portions 8 are formed in ranges corresponding to the ranges wherein are formed the p-type diffused resistance interconnections 6 in the n-type second semiconductor layer 3. In other words, the external conducting portions 8 are formed on top of the ranges wherein the p-type internal resistance portions are formed.
Additionally, a voltage is applied to those parts of the second semiconductor layer 3 that are not formed into the p-type diffused resistance interconnections 6 or into the differential pressure gauges 5 so as to be at the same electropotential or higher than that of the external conducting portions 8, and so that the potential difference formed between the diffused resistance interconnections 6 and the differential pressure gauges 5 of the second semiconductor layer 3 and those parts of the second semiconductor layer 3 that are not formed into the diffused resistance interconnections 6 or the differential pressure gauges 5 will be less than the breakdown voltage.
Here having the potential difference between the diffused resistance interconnections 6 and the differential pressure gauges 5 of the second semiconductor layer 3 and those parts of the second semiconductor layer 3 that are not formed into the diffused resistance interconnections 6 or the differential pressure gauges 5 be less than the breakdown voltage is because if this potential difference were to exceed the breakdown voltage, the pressure sensor would cease to function, and there would be the danger of destroying the pressure sensor. Specifically, if there were a large backward voltage from the n-type second semiconductor layer 3 to the p-type diffused resistance interconnections 6 and the differential pressure gauges 5, a sudden reverse current would result. Additionally, if the backward voltage were to exceed the specific breakdown voltage, the reverse current would suddenly increase, causing the pressure sensor to cease to function, and risking the destruction of the pressure sensor.
Note that if second semiconductor layer 3 is a p-type semiconductor substrate and the diffused resistance interconnections 6 and differential pressure gauges 5 are made from n-type semiconductor, then a voltage may be applied to those parts of the second semiconductor layer 3 that are not formed into the n-type diffused resistance interconnections 6 or into the differential pressure gauges 5 so as to be at the same electropotential or lower than that of the external conducting portions 8, and so that the potential difference formed between the diffused resistance interconnections 6 and the differential pressure gauges 5 of the second semiconductor layer 3 and those parts of the second semiconductor layer 3 that are not formed into the diffused resistance interconnections 6 or the differential pressure gauges 5 will be less than the breakdown voltage.
The method for manufacturing the sensor chip 10 will be explained next using
First an SOI (Silicon on Insulator) wafer is prepared having a first semiconductor layer 1, an insulating layer 2 with a thickness of about 0.5 μm, and a second semiconductor layer 3. In manufacturing this SOI wafer, the SIMOX (Separation by IMplanted OXygen) technology wherein an SiO2 layer is formed through implanting oxygen into a silicon substrate, may be used, the SDB (Silicon Direct Bonding) technology wherein two selecting substrates are bonded together, may be used, or another method may be used. Note that the second semiconductor layer 3 may be planarized and thinned. For example, the second semiconductor layer 3 may be polished the to a specific thickness using a polishing method known as CCP (Computer-Controlled Polishing).
The differential pressure gauges 5A through 5D are formed from p-type silicon, through an impurity diffusing method or an ion implantation method, on the top surface of the second semiconductor layer 3. Specifically, the differential pressure gauge 5 is formed through diffusing an impurity (such as boron) into the top surface of the second semiconductor layer 3. Also, similarly, diffused resistance interconnections 6 are formed (internal resistance portion forming process) on either side of the differential pressure gauges 5 on the top surface of the second semiconductor layer 3. Doing so forms the structure illustrated in
A resist 11 is formed on the bottom surface of the SOI wafer that is fabricated in this way. The pattern of the resist 11 is formed on the first semiconductor layer 1 through a well-known photolithography process. That is, a photosensitive resin layer is coated, exposed, and developed to form a pattern in the resist 11. The resist 11 has opening portions at parts that correspond to the pressure sensitive regions (the regions wherein the diaphragms will be formed). That is, the first semiconductor layer 1 is exposed in the parts wherein the diaphragms will be formed. Doing so forms the structure illustrated in
The first semiconductor layer 1 is etched using the resist 11 as a mask. Doing so forms the structure illustrated in
The structure illustrated in
The method for forming the pressure sensor will be explained next using
First, as illustrated in
Contact holes 12 are formed next through performing etching, using a photolithography method, as illustrated in
Following this, as illustrated in
Following this, as illustrated in
In the pressure sensor 100 according to an embodiment according to the present invention, the external conducting portions 8 are formed in ranges corresponding to the ranges wherein are formed the diffused resistance interconnections 6 in the second semiconductor layer 3. In other words, the external conducting portions 8 are formed on top of ranges wherein the diffused resistance interconnections 6 are formed. Doing so means that, as illustrated in
Furthermore, if second semiconductor layer 3 is an n-type semiconductor substrate and the diffused resistance interconnections 6 and differential pressure gauges 5 are made from p-type semiconductor, then a voltage is applied to those parts of the second semiconductor layer 3 that are not formed into the p-type diffused resistance interconnections 6 or into the differential pressure gauges 5 so as to be at the same electropotential or higher than that of the external conducting portions 8, and so that the potential difference formed between the diffused resistance interconnections 6 and the differential pressure gauges 5 of the second semiconductor layer 3 and those parts of the second semiconductor layer 3 that are not formed into the diffused resistance interconnections 6 or the differential pressure gauges 5 will be less than the breakdown voltage.
Doing so makes it possible to suppress to a trivial amount the current from the diffused resistance interconnections 6 to the portions of the second semiconductor layer 3 that are not formed into the diffused resistance interconnections 6. Consequently, this is able to prevent more effectively the characteristic defects in the pressure sensor 100.
Note that if second semiconductor layer 3 is a p-type semiconductor substrate and the diffused resistance interconnections 6 and differential pressure gauges 5 are made from n-type semiconductor, then a voltage should be applied to those parts of the second semiconductor layer 3 that are not formed into the n-type diffused resistance interconnections 6 or into the differential pressure gauges 5 so as to be at the same electropotential or lower than that of the external conducting portions 8, and so that the potential difference formed between the diffused resistance interconnections 6 and the differential pressure gauges 5 of the second semiconductor layer 3 and those parts of the second semiconductor layer 3 that are not formed into the diffused resistance interconnections 6 or the differential pressure gauges 5 will be less than the breakdown voltage.
Furthermore, the number of contacts 9 that are provided in the insulating layer is equal to the number of external conducting portions 8 or less than the number of external conducting portions 8.
If the number of contacts 9 is high, then, structurally, there will be a greater likelihood to be affected by stresses other than pressure. The present invention suppresses the number of contacts 9 to the minimum requirement, making it possible to reduce the effects of stresses other than pressure.
Note that in the pressure sensor 100 as set forth in the present invention, there is no limitation to the layout pattern for the individual gauges, or the like, to that which is in the present form of embodiment.
Additionally, the ranges wherein the external conducting portions 8 are formed may be controlled so that the ranges wherein the external conducting portions 8 are formed will be within ranges that correspond to the ranges wherein the diffused resistance interconnections 6 are formed in the second semiconductor layer 3. Additionally, the ranges wherein the diffused resistance interconnections 6 are formed may be controlled so that the ranges wherein the external conducting portions 8 are formed will be within ranges that correspond to the ranges wherein the diffused resistance interconnections 6 are formed in the second semiconductor layer 3. Additionally, both the ranges wherein the external conducting portions 8 are formed in the ranges wherein the diffused resistance interconnections 6 are formed may be controlled so that the ranges wherein the external conducting portions 8 are formed will be within ranges that correspond to the ranges wherein the diffused resistance interconnections 6 are formed in the second semiconductor layer 3.
The present invention can be applied also to pressure sensors having strain gauges having piezoresistance effects for static pressure as well.
Number | Date | Country | Kind |
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2009-159762 | Jul 2009 | JP | national |