JP2011164057A - Semiconductor pressure sensor, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor pressure sensor, capable of improving the destructive pressure resistance by reducing the stress concentration in the boundary between a part facing a recess and a part jointed to a first silicon substrate on the surface of a second silicon substrate facing the first silicon substrate, and to provide a method of manufacturing the semiconductor pressure sensor. <P>SOLUTION: This semiconductor pressure sensor includes the first silicon substrate 2 having a recess 8a in its one surface 3, the second silicon substrate 6 whose one surface 7 is joined to the first silicon substrate 2 so as to seal the recess 8a, a strain detecting element 13 formed on the other surface 12 of the second silicon substrate 6, and a first silicon oxide film 18 formed in a part of the one surface 7 of the second silicon substrate 6 that faces the recess 8a so as to cover the boundary between the part facing at least the recess 8a and the part joined to the one surface 3 of the first silicon substrate 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semiconductor pressure sensor formed using a semiconductor substrate and a manufacturing method thereof.

  Semiconductor pressure sensors formed using a semiconductor substrate can be produced in large quantities with high processing accuracy by using a semiconductor microfabrication technique. In a conventional semiconductor pressure sensor, a single crystal silicon layer is formed on a silicon substrate having a recess formed on an upper surface and a silicon oxide film so as to seal the recess through the silicon oxide film. The gauge resistance was provided on the diaphragm formed by the crystalline silicon layer. (For example, see Patent Document 1)

Japanese Patent No. 3570218 (pages 6-8, FIG. 2)

  In such a semiconductor pressure sensor, when the diaphragm is deformed due to a pressure difference between the pressure reference chamber surrounded by the concave portion of the silicon substrate and the diaphragm and the outside thereof, particularly, it faces the silicon substrate of the single crystal silicon layer. On the surface, stress tends to concentrate on the boundary between the part facing the recess and the part joined to the silicon substrate. This stress concentration may cause cracks to develop from the joint surface between the silicon substrate and the single crystal silicon layer, which is disadvantageous in terms of breakdown voltage.

  The present invention has been made to solve the above-described problems, and stress at the boundary between a portion facing the recess and a portion bonded to the silicon substrate on the surface facing the silicon substrate of the single crystal silicon layer. An object of the present invention is to provide a semiconductor pressure sensor and a method for manufacturing the same that can improve the breakdown voltage by reducing the concentration.

  A semiconductor pressure sensor according to the present invention includes a first semiconductor substrate having a recess formed on one surface, a second semiconductor substrate having one surface bonded to the first semiconductor substrate so as to seal the recess, (2) The strain detecting element formed on the other surface of the semiconductor substrate and the portion facing the recess on one surface of the second semiconductor substrate are joined to at least the portion facing the recess and one surface of the first semiconductor substrate. And a first oxide film formed so as to cover the boundary with the region.

  The method of manufacturing a semiconductor pressure sensor according to the present invention includes a step of forming a recess in one surface of the first semiconductor substrate, and one surface of the first semiconductor substrate and the second semiconductor substrate so as to seal the recess. And a portion facing one of the second semiconductor substrates facing the recess so as to cover at least the boundary between the portion facing the recess and the portion joined to one surface of the first semiconductor substrate. The method includes a step of forming a first oxide film and a step of forming a strain detection element on the other surface of the second semiconductor substrate.

  According to the semiconductor pressure sensor of the present invention, the first semiconductor substrate having a recess formed on one surface, and the second semiconductor substrate having one surface bonded to the first semiconductor substrate so as to seal the recess. A strain detecting element formed on the other surface of the second semiconductor substrate, a portion facing the recess on one surface of the second semiconductor substrate, at least a portion facing the recess and one surface of the first semiconductor substrate And a first oxide film formed so as to cover the boundary with the bonded portion, so that on one surface of the second semiconductor substrate, the portion facing the recess and one surface of the first semiconductor substrate Since the stress concentration at the boundary with the bonded portion can be alleviated, the breakdown voltage can be improved.

  According to the method of manufacturing a semiconductor pressure sensor according to the present invention, the step of forming a recess on one surface of the first semiconductor substrate, and one of the first semiconductor substrate and the second semiconductor substrate so as to seal the recess. A step of bonding the first semiconductor substrate and a portion of the second semiconductor substrate facing the concave portion at least on a surface of the second semiconductor substrate covering at least a boundary between the portion facing the concave portion and the portion bonded to the first surface of the first semiconductor substrate. The first oxide film is formed on the other surface of the second semiconductor substrate and the strain detecting element is formed on the other surface of the second semiconductor substrate. Since the stress concentration at the boundary between the part and the part joined to one surface of the first semiconductor substrate can be relaxed, the breakdown voltage can be improved.

It is sectional drawing which shows the semiconductor pressure sensor in Embodiment 1 of this invention. It is a top view which shows the 1st silicon substrate in Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the semiconductor pressure sensor in Embodiment 1 of this invention. It is sectional drawing which expands and shows the edge part of the recessed part of a semiconductor pressure sensor, (a) is sectional drawing which shows the semiconductor pressure sensor in Embodiment 1 of this invention, (b) is a 1st silicon oxide film and 3rd It is sectional drawing which shows the semiconductor pressure sensor which does not form a silicon oxide film. It is sectional drawing which shows the process of forming a recessed part in one surface of the 1st silicon substrate in Embodiment 2 of this invention. It is sectional drawing which shows the semiconductor pressure sensor in Embodiment 3 of this invention. It is sectional drawing which shows the process of forming the 1st alignment mark in Embodiment 3 of this invention. It is sectional drawing which shows the process of forming the 2nd alignment mark in Embodiment 3 of this invention. It is sectional drawing which shows the semiconductor pressure sensor in Embodiment 4 of this invention.

Embodiment 1 FIG.
First, the configuration of the semiconductor pressure sensor 1a according to the first embodiment of the present invention will be described. FIG. 1 is a cross-sectional view showing a semiconductor pressure sensor 1a according to Embodiment 1 of the present invention.

  In FIG. 1, a semiconductor pressure sensor 1a has a configuration in which one surface 3 of a first silicon substrate 2 and one surface 7 of a second silicon substrate 6 are joined. A concave portion 8a is formed on one surface 3 of the first silicon substrate 2, and the second silicon substrate 6 is joined to the first silicon substrate 2 so as to seal the concave portion 8a. By sealing the concave portion 8a with the second silicon substrate 6, the portion of the second silicon substrate 6 facing the concave portion 8a has a pressure in the space surrounded by the concave portion 8a and the second silicon substrate 6 and the second silicon substrate. Thus, the diaphragm 11 is deformed by a pressure difference from the external pressure on the other surface 12 side of 6. If the pressure in the space surrounded by the recess 8a and the second silicon substrate 6 is evacuated, the absolute pressure can be measured.

  At a predetermined position on the other surface 12 of the second silicon substrate 6, a strain detecting element 13 for detecting the strain of the diaphragm 11 as a resistance change is formed, and a wiring layer 16 for taking out an electric signal of the strain detecting element 13 to the outside is formed. Has been. The strain detection element 13 and the wiring layer 16 are covered with a protective film 17.

  Furthermore, a first silicon oxide film 18 is formed on a portion of the one surface 7 of the second silicon substrate 6 that faces the recess 8a. A second silicon oxide film 21 is formed on one surface 3 of the first silicon substrate 2 that is a surface bonded to the second silicon substrate 6. Therefore, the first silicon substrate 2 and the second silicon substrate 6 are bonded via the second silicon oxide film 21. Then, the first silicon oxide film 18 covers the boundary P between the portion facing the recess 8 a of the one surface 7 of the second silicon substrate 6 and the portion joined to the one surface 3 of the first silicon substrate 2. Is formed. That is, the first silicon oxide film 18 covers a portion of the bonding surface 22 between the first silicon substrate 2 and the second silicon substrate 6 that faces the recess 8a. Note that there is no clear boundary between the first silicon oxide film 18 and the second silicon oxide film 21, and they are formed so as to be integrated.

  A third silicon oxide film 23 is formed on the inner surface of the recess 8a. There is no clear boundary between the third silicon oxide film 23, the first silicon oxide film 18 and the second silicon oxide film 21, and they are formed so as to be integrated. A fourth silicon oxide film 27 is formed on the other surface 26 of the first silicon substrate 2.

  Here, the case where the film thicknesses of the first silicon oxide film 18 and the third silicon oxide film 23 are smaller than the film thicknesses of the second silicon oxide film 21 and the fourth silicon oxide film 27 is shown in FIG. Although described, the first silicon oxide film 18 and the third silicon oxide film 23 do not necessarily have to be thinner.

  Next, the first silicon substrate 2 will be described. Here, the first silicon substrate 2 is a single crystal silicon substrate having a plane orientation (100), and is preferably mirror-polished to a surface roughness Ra of 1 nm or less. The conductivity type and specific resistance value are not particularly limited, but it is preferably a P-type conductivity type with a specific resistance of about 1 to 10 Ω · cm.

  FIG. 2 is a top view showing first silicon substrate 2 according to the first embodiment of the present invention. As shown in FIG. 2, the first silicon substrate 2 is, for example, a square having a side of about 1 mm, and a recess 8 a is formed at the center of one surface 3. The concave portion 8a is a square whose planar shape is, for example, about 500 μm on a side and has a depth of about 10 to 100 μm. A third silicon oxide film 23 is formed on the inner surface of the recess 8a. The film thickness of the third silicon oxide film 23 is preferably in the range of 0.01 to 2 μm.

  Further, if the thickness of the second silicon oxide film 21 formed on the surface of the first silicon substrate 2 to be bonded to the second silicon substrate 6 is too thin, there is a possibility that a pinhole is formed. .1 μm or more is preferable, and a range of 0.2 to 3 μm is more preferable. The film thickness of the fourth silicon oxide film 27 formed on the other surface 26 of the first silicon substrate 2 is preferably the same as that of the second silicon oxide film 21. By forming the second silicon oxide film 21 and the fourth silicon oxide film 27 with the same film thickness, the warp of the first silicon substrate 2 can be prevented.

  Next, the second silicon substrate 6 will be described. Similarly to the first silicon substrate 2 described above, the second silicon substrate 6 is also a single crystal silicon substrate having a plane orientation (100), and is preferably mirror-polished to a surface roughness Ra of 1 nm or less. The conductivity type is not particularly limited, but when the strain detection element 13 is formed by ion implantation, the second silicon substrate 6 is preferably an N-type conductivity type. If the specific resistance value is too low, a current leaks from the strain detection element 13, and thus a higher specific resistance value is preferable, and it is preferably about 1 to 10 Ω · cm.

  The second silicon substrate 6 is also a square having a side of about 1 mm. The second silicon substrate 6 is joined to the first silicon substrate 2 so as to seal the recess 8 a, so that the portion of the second silicon substrate 6 facing the recess 8 a becomes the diaphragm 11. The maximum deflection amount of the diaphragm 11 is preferably 1 μm or less. For example, when the concave portion 8a is a square of 500 μm, the maximum deflection amount of the diaphragm 11 is 1 μm if the thickness of the second silicon substrate 6 is about 20 μm. The following can be suppressed.

  A first silicon oxide film 18 is formed on a portion of the one surface 7 of the second silicon substrate 6 that faces the recess 8a. The film thickness of the first silicon oxide film 18 is preferably in the range of 0.01 to 2 μm. A strain detecting element 13 is formed at a predetermined position on the other surface 12 of the second silicon substrate 6, and a wiring layer 16 and a protective film 17 are further formed.

  Next, the strain detection element 13 will be described. As a means for forming the strain detection element 13, for example, there is a method of forming an N-type region on a P-type substrate or a P-type region on an N-type substrate by ion implantation, or a method of forming a chromium film by a sputtering method. is there. From the viewpoint of detection sensitivity, a method of ion implantation is preferable to a method of forming a chromium film, and a method of forming a P-type region on an N-type substrate rather than a method of forming an N-type region on a P-type substrate. Is preferred. Therefore, when the P-type strain detecting element 13 is formed by ion implantation, the second silicon substrate 6 is an N-type conductivity type.

  A metal film such as aluminum, copper, gold, silver, or the like is used as the wiring layer 16 that extracts an electric signal from the strain detection element 13 to the outside. As the protective film 17 that covers the strain detection element 13 and the wiring layer 16, a silicon nitride film that does not transmit moisture is suitable.

  Next, a method for manufacturing the semiconductor pressure sensor 1a according to the first embodiment of the present invention will be described. FIG. 3 is a sectional view showing a manufacturing process for the semiconductor pressure sensor 1a according to the first embodiment of the present invention.

  First, as shown in FIG. 3A, a first silicon substrate 2 is prepared. Here, the first silicon substrate 2 is a P-type conductivity type and is a single crystal silicon substrate having a plane orientation (100).

  Next, as shown in FIG. 3B, a second silicon oxide film 21 is formed on one surface 3 of the first silicon substrate 2, and a fourth silicon oxide film 27 is formed on the other surface 26. As a method of forming the second silicon oxide film 21 and the fourth silicon oxide film 27, there are a thermal oxidation method, a plasma CVD (Chemical Vapor Deposition) method, and the like, but a thermal oxidation method that can easily form a dense silicon oxide film is used. It is preferable to use it. Therefore, here, the second silicon oxide film 21 and the fourth silicon oxide film 27 are formed by annealing the first silicon substrate 2 in an oxidizing atmosphere using a thermal oxidation method.

  Next, as shown in FIG. 3C, a photosensitive resin 28 is applied onto the second silicon oxide film 21 on the one surface 3 of the first silicon substrate 2 by spin coating, and photosensitivity is applied by photolithography. The resin 28 is patterned into a desired shape.

  Next, as shown in FIG. 3D, the portion of the second silicon oxide film 21 that is not covered with the photosensitive resin 28 is removed. As the removing means, a solution added with hydrofluoric acid or ammonia fluoride, or plasma etching in which tetrafluoromethane gas and oxygen gas are mixed can be used.

  Next, as shown in FIG. 3E, the silicon portion exposed by removing the second silicon oxide film 21 in the previous step on one surface 3 of the first silicon substrate 2 is etched to form a recess 8a. Form. As an etching means, plasma etching using sulfur hexafluoride gas is used. When plasma etching is performed, perfluorocyclobutane gas and sulfur hexafluoride gas are alternately introduced so that etching can be performed approximately vertically.

  Next, as shown in FIG. 3F, the photosensitive resin 28 remaining on the second silicon oxide film 21 is removed. As the removing means, removal with an organic solvent such as acetone or removal with oxygen plasma is used. However, in the case of removal by plasma, it is necessary to control the power of the plasma and reduce damage caused by irradiated ions so that the surface roughness Ra of the second silicon oxide film 21 does not exceed 1 nm.

  Next, the surface of the first silicon substrate 2 is subjected to a hydrophilic treatment. For example, the first silicon substrate 2 is cleaned for about 10 minutes by a solution in which concentrated sulfuric acid having a concentration of 98% and hydrogen peroxide solution having a concentration of 30% are mixed at a volume ratio of 4: 1 and heated to 130 ° C. As a result, the surface of the first silicon substrate 2 is made hydrophilic, and a good surface state is obtained when the first silicon substrate 2 and the second silicon substrate 6 are temporarily joined at room temperature.

  Next, as shown in FIG. 3G, one surface 3 of the first silicon substrate 2 and one surface 7 of the second silicon substrate 6 are sealed so as to seal the recess 8a of the first silicon substrate 2. Are temporarily bonded via the second silicon oxide film 21. Here, the second silicon substrate 6 is a single crystal silicon substrate of N-type conductivity and having a plane orientation (100). Further, the thickness of the second silicon substrate 6 is thicker than a thickness suitable for forming the diaphragm 11.

  At this time, the temperature may be room temperature. Either the atmosphere or the vacuum may be used, but when it is desired to make the space surrounded by the recess 8a and the second silicon substrate 6 serving as the pressure reference chamber of the semiconductor pressure sensor 1a, the temporary bonding may be performed in the vacuum. preferable. Here, since the moisture remaining in the space surrounded by the recess 8a and the second silicon substrate 6 is used in a later process, a vacuum state of about 1 Pa or higher is suitable.

  Next, an annealing process is performed. Here, annealing treatment in an oxidizing atmosphere such as an oxygen or water vapor atmosphere is suitable. The annealing temperature is preferably in the range of 1000 to 1200 ° C., and the annealing time is preferably 1 hour or longer, more preferably about 6 hours. By this annealing treatment, the first silicon substrate 2 and the second silicon substrate 6 that were in the temporarily bonded state are completely bonded.

  Further, as shown in FIG. 3 (h), one surface 7 of the second silicon substrate 6 is utilized by utilizing the moisture remaining in the space surrounded by the recess 8a and the second silicon substrate 6 by this annealing process. Thus, the first silicon oxide film 18 is formed on the portion facing the recess 8a, and the third silicon oxide film 23 is formed on the inner surface of the recess 8a. Here, the first silicon oxide film 18 covers the boundary between the portion facing the recess 8 a of the one surface 7 of the second silicon substrate 6 and the portion joined to the one surface 3 of the first silicon substrate 2. It will be. That is, a portion of the bonding surface 22 between the first silicon substrate 2 and the second silicon substrate 6 that faces the recess 8 a is covered with the first silicon oxide film 18. There is no clear boundary between the first silicon oxide film 18, the second silicon oxide film 21, and the third silicon oxide film 23, and they are formed so as to be integrated.

  In this case, the thickness of the first silicon oxide film 18 and the third silicon oxide film 23 formed by the annealing process is smaller than the thickness of the second silicon oxide film 21 and the fourth silicon oxide film 27. However, the thickness of the first silicon oxide film 18 and the third silicon oxide film 23 may be larger.

  Next, as shown in FIG. 3I, the second silicon substrate 6 is thinned to a desired thickness. As a result, the portion of the second silicon substrate 6 that faces the recess 8 a becomes the diaphragm 11. As the thickness of the second silicon substrate 6 is reduced, the maximum deflection amount of the diaphragm 11 is increased. However, it is preferable that the thinning is performed so that the maximum deflection amount of the diaphragm 11 is 1 μm or less. As a means for thinning, a grinder and a chemical mechanical polishing technique may be used.

  Next, as shown in FIG. 3 (j), a strain detection element 13 is formed at a predetermined position on the other surface 12 of the second silicon substrate 6. Since the strain detecting element 13 is preferably formed in a portion where the distortion of the diaphragm 11 is large, the end portion or the center portion of the diaphragm 11 is preferable. In FIG. 3 (j), it is formed at the end of the diaphragm 11.

  By irradiating white light including light having a wavelength of 1000 nm or more from the other surface 26 side of the first silicon substrate 2 and observing near infrared light transmitted through the second silicon substrate 6 with an infrared camera, The position can be accurately determined. Thereby, the position where the strain detection element 13 is formed can be determined with respect to the position of the recess 8a.

  As a means for forming the strain detection element 13, as described above, from the viewpoint of detection sensitivity, for example, boron is ion-implanted to form a P-type region on the other surface 12 of the second silicon substrate 6 of the N-type conductivity type. Preferably formed.

  Finally, a wiring layer 16 and a protective film 17 are formed on the other surface 12 of the second silicon substrate 6. It is preferable to use an aluminum film as the wiring layer 16 and a silicon nitride film as the protective film 17.

  Next, an example in which the breakdown voltage is compared between the semiconductor pressure sensor 1a according to the first embodiment of the present invention and the semiconductor pressure sensor 31 in which the first silicon oxide film 18 and the third silicon oxide film 23 are not formed will be described. FIG. 4 is an enlarged cross-sectional view showing the end of the recess of the semiconductor pressure sensor, (a) is a cross-sectional view showing the semiconductor pressure sensor 1a according to Embodiment 1 of the present invention, and (b) is the first oxidation. 4 is a cross-sectional view showing a semiconductor pressure sensor 31 in which a silicon film 18 and a third silicon oxide film 23 are not formed. However, in FIG. 4, the wiring layer 16 and the protective film 17 are omitted.

  First, the configuration of the semiconductor pressure sensor 1a and the semiconductor pressure sensor 31 used in the comparative experiment will be described. In the semiconductor pressure sensor 1a according to the first embodiment of the present invention shown in FIG. 4A, the planar shape of the recess 8a is a square having a side of 500 μm, and the thickness of the second silicon substrate 6 is 20 μm. . The semiconductor pressure sensor 31 of the comparative example shown in FIG. 4B has the same configuration as the semiconductor pressure sensor 1a except that the first silicon oxide film 18 and the third silicon oxide film 23 are not formed.

In the semiconductor pressure sensor 1a, the pressure at the time of joining the first silicon substrate 2 and the second silicon substrate 6 is about 1 Pa, so that moisture remains in the space surrounded by the recesses 8a and the second silicon substrate 6. Then, the first silicon oxide film 18 and the third silicon oxide film 23 were formed by thermal oxidation by the subsequent annealing process. On the other hand, in the semiconductor pressure sensor 31, since the pressure is reduced to about 10 ⁻⁴ Pa and moisture remaining in the space surrounded by the concave portion 8a and the second silicon substrate 6 is removed as much as possible, bonding is performed thereafter. The first silicon oxide film 18 and the third silicon oxide film 23 were not formed even by the annealing process.

  Next, the result of the comparative experiment will be described. The semiconductor pressure sensor 31 was broken at 5 to 8 MPa as the external pressure was increased. In contrast, in the semiconductor pressure sensor 1a according to the first embodiment of the present invention, when the external pressure was increased, the semiconductor pressure sensor 1a was broken at 12 to 15 MPa. Even when the experiment was performed by changing the dimensions of the recess 8a and the thickness of the second silicon substrate 6, the absolute values of the respective breakdown pressure values increased and decreased, but the breakdown pressure of the semiconductor pressure sensor 1a is higher. Did not change.

  As shown in FIG. 4B, in the semiconductor pressure sensor 31 of the comparative example, when the diaphragm 11 bends, the portion facing the recess 8a on the one surface 7 of the second silicon substrate 6 and the first silicon substrate. Since stress is particularly concentrated at point B, which is the boundary between one surface 3 of 2 and the joined portion, cracks are likely to develop from the joining surface 22. On the other hand, as shown in FIG. 4A, in the semiconductor pressure sensor 1a according to the first embodiment of the present invention, the first silicon oxide film 18 is formed at a portion facing the recess 8a on one surface 7 of the second silicon substrate 6. As a result, the point where stress concentrates when the diaphragm 11 is bent becomes the point A away from the joint surface 22. Therefore, in the semiconductor pressure sensor 1a, the boundary between the portion facing the recess 8a and the portion joined to the one surface 3 of the first silicon substrate 2 on the one surface 7 of the second silicon substrate 6, that is, the first It is possible to alleviate stress concentration on the portion of the bonding surface 22 between the silicon substrate 2 and the second silicon substrate 6 that faces the recess 8a.

  In the first embodiment of the present invention, the configuration as described above allows bonding of the portion facing the recess 8a and the one surface 3 of the first silicon substrate 2 on one surface 7 of the second silicon substrate 6. Since the stress concentration at the boundary with the formed portion can be relaxed, there is an effect that the breakdown voltage is improved.

  Further, since silicon oxide is more easily hydrophilized than silicon, by forming the second silicon oxide film 21 on one surface 3 which is a surface bonded to the second silicon substrate 6 of the first silicon substrate 2, One surface 3 is made more hydrophilic than the state in which the second silicon oxide film 21 is not formed. For this reason, joining of the 1st silicon substrate 2 and the 2nd silicon substrate 6 becomes easy.

  Further, by forming the fourth silicon oxide film 27 on the other surface 26 of the first silicon substrate 2, the second silicon oxide film 21 and the fourth silicon oxide film 27 are formed on the front and back of the first silicon substrate 2. As a result, the warp of the first silicon substrate 2 can be suppressed.

  By forming the third silicon oxide film 23 on the inner surface of the concave portion 8a of the first silicon substrate 2, the third silicon oxide film 23 becomes the concave portion 8a and the second silicon substrate 6 serving as a pressure reference chamber of the semiconductor pressure sensor 1a. It will play a role of absorbing moisture remaining in the space surrounded by. Thereby, since the residual moisture in the space surrounded by the recess 8a and the second silicon substrate 6 can be reduced, the remaining water molecules can be prevented from adversely affecting the pressure detection.

  The second silicon oxide film 21 is formed by thermal oxidation after the concave portion 8a is formed on the one surface 3 of the first silicon substrate 2 and before the first silicon substrate 2 and the second silicon substrate 6 are bonded. Is formed on the surface of the first silicon substrate 2 to be bonded to the second silicon substrate, the temperature distribution differs between the portion around the recess 8a and the portion away from the recess 8a. The thickness of the second silicon oxide film 21 is not uniform within the one surface 3 of the substrate 2. If the thickness of the second silicon oxide film 21 is not uniform, a defect occurs in the bonding between the first silicon substrate 2 and the second silicon substrate 6. On the other hand, in the first embodiment of the present invention, the second silicon oxide film 21 is formed by forming the second silicon oxide film 21 before forming the recess 8a on the one surface 3 of the first silicon substrate 2. Can be formed to be uniform within one surface 3 of the first silicon substrate 2. Thereby, it is possible to prevent a defect from occurring in the bonding between the first silicon substrate 2 and the second silicon substrate 6.

  In the first embodiment of the present invention, the first silicon oxide film 18 is formed on the entire surface of the portion of the second silicon substrate 6 that faces the recess 8a. However, the present invention is not limited to this, and at least one portion of the surface of the second silicon substrate 6 facing the recess 8a and the portion facing the recess 8a and the one surface 3 of the first silicon substrate 2 are joined. If it is formed so as to cover the boundary with the part, a certain effect can be obtained.

  In the first embodiment of the present invention, the second silicon oxide film 21 is formed on the entire surface of the first silicon substrate 2 to be bonded to the second silicon substrate 6. However, the present invention is not limited to this, and the concave portion 8a is sealed by the second silicon substrate 6 at least at a portion corresponding to the periphery of the concave portion 8a on the surface bonded to the second silicon substrate 6 of the first silicon substrate 2. It is sufficient that it is formed in a sufficient amount.

  The same applies to the fourth silicon oxide film 27 formed on the other surface 26 of the first silicon substrate 2, and it is not always necessary to form it on the entire surface. The fourth silicon oxide film 27 is preferably formed so that the warp of the first silicon substrate 2 is reduced in relation to the second silicon oxide film 21 and the third silicon oxide film 23.

  Furthermore, in the first embodiment of the present invention, the third silicon oxide film 23 is formed on the entire inner surface of the recess 8a, and the third silicon oxide film 23, the first silicon oxide film 18 and the second silicon oxide film 21 are formed. There was no clear boundary between them, and they were formed to be united. However, it is not necessary to form the third silicon oxide film 23 on the entire inner surface of the recess 8a. Even if it is formed only on a part of the inner surface of the recess 8a, a certain effect can be obtained. Further, the same effect can be obtained even if the third silicon oxide film 23 is formed so as to be separated from the first silicon oxide film 18 and the second silicon oxide film 21 without being integrated.

  In the first embodiment of the present invention, the second silicon substrate 6 is thicker than necessary for forming the diaphragm 11 and is thinned to a desired thickness after being joined to the first silicon substrate 2. did. However, the thinning process may be performed before bonding to the first silicon substrate 2, or the second silicon substrate 6 may be prepared and used with a thickness that does not require thinning from the beginning. Good.

  In the first embodiment of the present invention, the second silicon oxide film 21 on one surface 3 of the first silicon substrate 2 and the fourth silicon oxide film 27 on the other surface 26 are formed before the recess 8a is formed. Formed simultaneously. However, it is not necessary to be simultaneous, and the fourth silicon oxide film 27 may be formed at any time. However, it is preferable to form the first silicon substrate 2 and the second silicon substrate 6 before joining them.

  Also for the second silicon oxide film 21, the film thickness of the second silicon oxide film 21 is uniformly formed by appropriately managing the temperature distribution in the one surface 3 of the first silicon substrate 2 during annealing. If possible, it may be formed after the recess 8a is formed.

  In addition, in the first embodiment of the present invention, the first silicon oxide film 18 and the third silicon oxide film 23 are formed simultaneously. However, the present invention is not limited to this, and the third silicon oxide film 23 may be formed before the first silicon substrate 2 and the second silicon substrate 6 are joined.

  In the first embodiment of the present invention, the first silicon substrate 2 and the second silicon substrate 6 which are silicon substrates are used. However, the present invention is not limited to this, and other semiconductor substrates such as silicon carbide and germanium are used. It may be used.

  The shapes of the first silicon substrate 2 and the second silicon substrate 6 are square here, but may be other shapes. The recess 8a is also formed by making the planar shape square and etching vertically in the depth direction, but other shapes may be used.

  The first silicon substrate 2 and the second silicon substrate 6 have the same shape and size, but the second silicon substrate 6 is at least large enough to seal the recess 8a and form the diaphragm 11. Is enough.

Embodiment 2. FIG.
FIG. 5 is a cross-sectional view showing a step of forming a recess 8b in one surface 3 of first silicon substrate 2 in the second embodiment of the present invention. In FIG. 5, the same reference numerals as those in FIG. 3E denote the same or corresponding components, and the description thereof is omitted. The first embodiment of the present invention is different from the first embodiment in that the concave portion 8b is not shaped perpendicular to the depth direction, but becomes thinner as it advances in the depth direction.

  Next, a process for forming such a recess 8b will be described. As shown in FIG. 5, the exposed portion of silicon on one surface 3 of the first silicon substrate 2 is etched to form a recess 8b. As an etching means, etching with an alkaline solution such as an aqueous potassium hydroxide solution is used. The potassium hydroxide aqueous solution exhibits anisotropy with respect to the crystal orientation of silicon, and etching hardly proceeds on the (111) plane. Here, since a single crystal silicon substrate having a plane orientation (100) is used as the first silicon substrate 2, by using a potassium hydroxide aqueous solution, a (111) plane appears and becomes thinner as it advances in the depth direction. A concave portion 8b having a shape is formed.

  In the case where the recess 8b is formed by etching using an alkaline solution, the photosensitive resin 28 is dissolved by the alkaline solution and may adversely affect the etching of silicon. Therefore, before the step of forming the recess 8b, It is preferable to remove the photosensitive resin 28 in advance. Other steps are the same as those in the first embodiment of the present invention.

  In the second embodiment of the present invention, since the manufacturing process is as described above, the manufacturing cost can be reduced as compared with the case where the recess 8a is formed by plasma etching.

Embodiment 3 FIG.
FIG. 6 is a sectional view showing a semiconductor pressure sensor 1b according to the third embodiment of the present invention. In FIG. 6, the same reference numerals as those in FIG. 1 denote the same or corresponding components, and the description thereof is omitted. In the first embodiment of the present invention, the first alignment mark 32 is formed on the other surface 26 of the first silicon substrate 2 and the second alignment mark is formed on the other surface 12 of the second silicon substrate 6. Is different. The first alignment mark 32 serves as a mark indicating a relative position with respect to the recess 8 a, and the second alignment mark 33 serves as a mark indicating a relative position with respect to the first alignment mark 32.

  However, here, a case where the fourth silicon oxide film 27 is not formed will be described. In FIG. 6, the wiring layer 16 and the protective film 17 are omitted.

  Next, the process of forming the first alignment mark 32 will be described. FIG. 7 is a cross-sectional view showing a step of forming first alignment mark 32 in the third embodiment of the present invention. This step is performed after the step of forming the recess 8a shown in FIG. 3E or the step of removing the photosensitive resin 28 shown in FIG.

  The first alignment mark 32 is formed on the other surface 26 of the first silicon substrate 2 by patterning a photosensitive resin by photolithography and etching a portion that is not covered with the photosensitive resin. The shape of the first alignment mark 32 is not particularly limited, such as a square shape, a rectangular shape, a circular shape, or a slit shape.

  The photomask for patterning the first alignment mark 32 is positioned by observing an image obtained by superimposing an image obtained by observing the first silicon substrate 2 from the one surface 3 side and an image observed from the other surface 26 side. Do it. From this superimposed observation image, the position of the concave portion 8a or the position of another mark formed with a precise relative position to the concave portion 8a on one surface 3 of the first silicon substrate 2 is used as a reference. Perform positioning. Thus, the first alignment mark 32 whose relative position with respect to the recess 8a is accurately determined can be formed.

  Next, the process of forming the second alignment mark 33 will be described. FIG. 8 is a sectional view showing a step of forming second alignment mark 33 in the third embodiment of the present invention. This step is performed after the step of thinning the second silicon substrate 6 shown in FIG.

  Similarly to the first alignment mark 32, the second alignment mark 33 is formed by patterning the other surface 12 of the second silicon substrate 6 by photolithography and then performing etching. Similarly to the first alignment mark 32, the shape of the second alignment mark 33 is not particularly limited.

  The photomask for patterning the second alignment mark 33 is positioned by superimposing an image observed from the other surface 26 side of the first silicon substrate 2 and an image observed from the other surface 12 side of the second silicon substrate 6. Observe the combined image. From this superimposed observation image, the photomask is positioned using the position of the first alignment mark 32 as a reference. Thus, the second alignment mark 33 whose relative position with the first alignment mark 32 is accurately determined can be formed. Since the relative position of the first alignment mark 32 with the concave portion 8a is determined with high accuracy, the second alignment mark 33 is formed with the relative position of the concave portion 8a with high accuracy.

  Next, a process of forming the strain detection element 13 on the other surface 12 of the second silicon substrate 6 will be described. When positioning for forming the strain detection element 13 is performed, positioning is performed using the second alignment mark 33 formed on the other surface 12 of the second silicon substrate 6 as a mark. Since the relative position between the recess 8a and the second alignment mark 33 is accurately determined, the strain detection element 13 can be formed at an appropriate position on the diaphragm 11 by using the second alignment mark 33 as a mark. it can.

  In Embodiment 3 of the present invention, with the above-described configuration, visible light can be obtained without using near-infrared light in the step of forming the strain detection element 13 on the other surface 12 of the second silicon substrate 6. The position where the strain detection element 13 is formed can be determined by observation at. This eliminates the need for a device that irradiates near-infrared light, so that the device configuration can be simplified.

  In the third embodiment of the present invention, the first alignment mark 32 and the second alignment mark 33 are formed. However, even when only the first alignment mark 32 is formed and the second alignment mark 33 is not formed, the strain detection element 13 can be positioned in the visible light observation. In the case of only the first alignment mark 32, an image observed from the other surface 26 side of the first silicon substrate 2 and the other surface 12 side of the second silicon substrate 6 when determining the formation position of the strain detection element 13 are determined. This is done by observing an image superposed on the image observed from above. The strain detection element 13 can be formed at an appropriate position on the diaphragm 11 by determining the position at which the strain detection element 13 is formed from the superposed observation image using the first alignment mark 32 as a mark.

  Furthermore, in Embodiment 3 of the present invention, after the recess 8a is formed, the position of the recess 8a or the relative position with respect to the recess 8a is determined on the one surface 3 of the first silicon substrate 2 with high accuracy. The first alignment mark 32 was formed with reference to the position of the mark. However, conversely, after forming the first alignment mark 32, the recess 8a may be formed with reference to the position of the first alignment mark 32.

  In the third embodiment of the present invention, the case where the fourth silicon oxide film 27 is not formed on the other surface 26 of the first silicon substrate 2 has been described. However, the fourth silicon oxide film 27 is formed. Also good. In this case, the first alignment mark 32 may be formed on the fourth silicon oxide film 27.

Embodiment 4 FIG.
FIG. 9 is a sectional view showing a semiconductor pressure sensor 1c according to the fourth embodiment of the present invention. 9, the same reference numerals as those in FIG. 1 denote the same or corresponding components, and the description thereof is omitted. The first embodiment of the present invention is different from the first embodiment in that a through hole 36 penetrating from the other surface 26 of the first silicon substrate 2 to the recess 8a is formed.

  However, here, a case where the fourth silicon oxide film 27 is not formed will be described. In FIG. 9, the wiring layer 16 and the protective film 17 are omitted.

  The through hole 36 is formed by etching, but the forming means is not particularly limited as long as a hole penetrating from the other surface 26 of the first silicon substrate 2 to the recess 8a can be formed. Further, the shape, size and position of the through hole 36 are not particularly limited. The step of forming the through hole 36 is preferably performed after the step of forming the strain detection element 13.

  In the fourth embodiment of the present invention, the pressure between the pressure on the other surface 26 side of the first silicon substrate 2 and the pressure on the other surface 12 side of the second silicon substrate 6 is obtained by adopting the above configuration. Differences can be detected.

  In the fourth embodiment of the present invention, the case where the fourth silicon oxide film 27 is not formed on the other surface 26 of the first silicon substrate 2 has been described. However, the fourth silicon oxide film 27 is formed. Even in this case, the same effect can be obtained if the through hole 36 is formed so as to penetrate from the other surface 26 side of the first silicon substrate 2 to the recess 8a.

  The first to fourth embodiments of the present invention have been described above. These configurations described in the first to fourth embodiments of the present invention can be combined with each other.

1a to 1c Semiconductor pressure sensor 2 First silicon substrate 3 One surface of first silicon substrate 6 Second silicon substrate 7 One surface of second silicon substrate 8a, 8b Recessed portion 12 Other surface of second silicon substrate 13 Strain detection Element 18 First silicon oxide film 21 Second silicon oxide film 22 Bonding surface between first silicon substrate and second silicon substrate 23 Third silicon oxide film 26 Other surface of first silicon substrate 27 Fourth silicon oxide film 32 First 1 alignment mark 33 2nd alignment mark 36 through hole

Claims (12)

A first semiconductor substrate having a recess formed on one surface;
A second semiconductor substrate having one surface bonded to the first semiconductor substrate so as to seal the recess,
A strain sensing element formed on the other surface of the second semiconductor substrate;
The portion of the second semiconductor substrate facing the recess is formed so as to cover at least the boundary between the portion facing the recess and the portion joined to the one surface of the first semiconductor substrate. A first oxide film;
Semiconductor pressure sensor equipped with.   A second oxide film is formed at least around the recess on the surface of the first semiconductor substrate bonded to the second semiconductor substrate, and the second oxide film is integrated with a part of the first oxide film. The semiconductor pressure sensor according to claim 1, wherein:   The semiconductor pressure sensor according to claim 1, wherein a third oxide film is formed on an inner surface of the concave portion of the first semiconductor substrate.   4. The semiconductor pressure sensor according to claim 2, wherein a fourth oxide film is formed on the other surface of the first semiconductor substrate.   5. The semiconductor pressure sensor according to claim 1, wherein a through-hole penetrating from the other surface of the first semiconductor substrate to the concave portion is formed. Forming a recess on one surface of the first semiconductor substrate;
Bonding one surface of the first semiconductor substrate and the second semiconductor substrate so as to seal the recess,
The first oxidation is performed so that one surface of the second semiconductor substrate faces the recess and covers at least the boundary between the portion facing the recess and the portion joined to one surface of the first semiconductor substrate. Forming a film;
Forming a strain sensing element on the other surface of the second semiconductor substrate;
Of manufacturing a semiconductor pressure sensor comprising:   A step of forming a second oxide film so as to be integrated with a part of the first oxide film at least around a recess on a surface of the first semiconductor substrate bonded to the second semiconductor substrate. A method for manufacturing a semiconductor pressure sensor according to claim 6.   8. The method of manufacturing a semiconductor pressure sensor according to claim 6, further comprising a step of forming a third oxide film on the inner surface of the concave portion of the first semiconductor substrate.   9. The method of manufacturing a semiconductor pressure sensor according to claim 7, further comprising a step of forming a fourth oxide film on the other surface of the first semiconductor substrate.   The method for manufacturing a semiconductor pressure sensor according to claim 6, further comprising a step of thinning the second semiconductor substrate to a desired thickness. Forming a first mark portion indicating a relative position with respect to the concave portion on the other surface of the first semiconductor substrate;
11. The strain detection element is formed using the first mark portion as a mark in the step of forming the strain detection element on the other surface of the second semiconductor substrate. 11. The manufacturing method of the semiconductor pressure sensor of description. Forming a first mark portion indicating a relative position with respect to the concave portion on the other surface of the first semiconductor substrate;
Forming a second mark portion indicating a relative position with respect to the first mark portion on the other surface of the second semiconductor substrate;
With
11. The strain detection element is formed using the second mark portion as a mark in the step of forming a strain detection element on the other surface of the second semiconductor substrate. The manufacturing method of the semiconductor pressure sensor of claim | item.

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