JP2013145154A - Semiconductor pressure sensor and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor pressure sensor and a manufacturing method thereof which are capable of suppressing an upward bulge at corners of a substrate with surfaces covered by a thermal oxide insulating film, and avoiding connection failure of the substrate associated with formation of a pressure reference chamber.SOLUTION: An embodiment comprises: a first substrate having a main surface and a thermal oxide insulating layer inside a recess formed in the main surface; and a second substrate having a diaphragm which has strain gauges and wiring and faces the recess. An opening of the recess is formed in a rectangular shape having corners looked round in top view.

Description

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

  A semiconductor pressure sensor formed using a semiconductor substrate can be mass-produced with high processing accuracy by using a semiconductor microfabrication technology, and can provide a high-performance and low-cost sensor. .

  As a conventional semiconductor pressure sensor, for example, in Japanese Patent Application Laid-Open No. 11-298209 (Patent Document 1), a concave portion is formed on a top surface of a silicon substrate on which a concave portion is formed and a silicon oxide film is formed. A semiconductor pressure sensor having a structure in which a single crystal silicon layer is formed so as to seal and a strain gauge is provided on a pressure receiving portion formed by a single crystal silicon layer provided at a position opposite to the concave portion is disclosed. Yes.

  In the manufacturing process of the semiconductor pressure sensor, various processes are performed on the wafer-like silicon substrate, and the wafer is cut out like a grid by dicing at the final stage. Therefore, generally, the external shape of the semiconductor pressure sensor is a rectangular shape. In such a semiconductor pressure sensor, when the shape of the pressure receiving portion is a rectangular shape that is similar to the outer shape of the element, it is advantageous that the maximum sensitivity can be obtained as a sensor with a limited element area.

  Next, the maximum sensitivity of the semiconductor pressure sensor will be described. The maximum sensitivity of the semiconductor pressure sensor is determined by the ease with which the pressure receiving portion bends. For example, when the pressure receiving portion is designed to be a circle inscribed in a rectangle, the ease of bending is reduced to approximately 0.76 times that in the case where the pressure receiving portion is designed to be a rectangle, and the sensitivity of the semiconductor pressure sensor accordingly. Decreases and performance decreases.

  On the other hand, when the pressure receiving part is designed to be a circle circumscribing the rectangle, the ease of bending is greater than when the pressure receiving part is designed to be rectangular, but the metal film pattern for electric wiring provided around the pressure receiving part As a result, the outer shape of the semiconductor pressure sensor is increased. As the semiconductor pressure sensor becomes larger, the number of elements that can be taken from the wafer decreases and the cost increases.

  As described above, it is advantageous that the pressure receiving portion has a rectangular shape similar to the outer shape of the element, and the shape of the pressure receiving portion is defined by the planar shape of the concave portion provided in the opposite silicon substrate. Becomes a rectangle.

  Here, the silicon oxide film formed on the upper surface of the silicon substrate of the semiconductor pressure sensor will be described. The silicon oxide film formed on the upper surface of the silicon substrate is preferably a thermal oxide film. The thermal oxide film is, for example, a film formed by bottom-up by heating a silicon substrate at about 1000 ° C. in an atmosphere containing moisture to oxidize silicon. The surface of the thermal oxide film thus formed is smoother when viewed microscopically than the surface of the oxide film formed by top-down vapor phase growth such as CVD (Chemical Vapor Deposition). Therefore, the silicon oxide film formed on the upper surface of the silicon substrate having the recesses is used as a thermal oxide film, so that a good bonding can be achieved when the single crystal silicon layer is bonded to the upper surface of the silicon substrate to provide the pressure receiving portion. can get.

Japanese Patent Laid-Open No. 11-298209

  However, when silicon is thermally oxidized, the volume expands, and its value is about 2.3 times that of the original silicon. Since distortion due to volume expansion occurs not only in the thickness direction of the substrate but also in the planar direction, strain in different directions concentrates on the opening end of the recess provided on the upper surface of the silicon substrate, and an upward bulge occurs. For this reason, the bulge at the opening end of the substrate hinders the bonding of the substrates for sealing the recess, and there is a problem of inducing bonding failure.

  The present invention has been made to solve the above-described problems, and a first substrate having a concave portion formed on the main surface and an insulating layer formed by thermal oxidation is provided on the first substrate via the insulating layer. In the semiconductor pressure sensor in which the second substrate is bonded so as to seal the recess and the strain gauge is formed on the pressure receiving portion formed by the second substrate provided at a position facing the recess. The present invention provides a semiconductor pressure sensor and a method for manufacturing the semiconductor pressure sensor that can avoid a bonding failure of a substrate related to sealing of the substrate.

  In the semiconductor pressure sensor according to the present invention, a main substrate and a first substrate having a thermal oxidation insulating layer on an inner surface of a recess formed on the main surface, and a diaphragm having a wiring and a strain gauge are provided to face the recess. A semiconductor pressure sensor comprising a second substrate, wherein the opening shape of the recess is a rectangular shape having round corners as viewed from above.

  The semiconductor pressure sensor according to the present invention includes a first substrate having a thermal oxidation insulating layer on a main surface and an inner surface of a recess formed on the main surface, and a diaphragm having a wiring and a strain gauge facing the recess. A semiconductor pressure sensor comprising: a second substrate, wherein the opening shape of the concave portion is a polygonal shape having an obtuse corner when viewed from above.

  The semiconductor pressure sensor according to the present invention includes a first substrate having a thermal oxidation insulating layer on a main surface and an inner surface of a recess formed on the main surface, and a diaphragm having a wiring and a strain gauge facing the recess. A semiconductor pressure sensor comprising a second substrate, wherein a corner formed by a main surface and an inner wall surface of a recess has a chamfered shape.

  According to the semiconductor pressure sensor of the present invention, the first substrate having the thermal oxidation insulating layer on the main surface and the inner surface of the recess formed on the main surface, and the diaphragm having the wiring and the strain gauge are provided facing the recess. In addition, since the opening shape of the concave portion is a rectangular shape with rounded corners when viewed from above, it is possible to prevent the thermal oxide insulating layer from rising and to prevent sealing. It is possible to avoid poor bonding of the substrates.

  Further, according to the semiconductor pressure sensor of the present invention, the first substrate having the thermal oxidation insulating layer on the main surface and the inner surface of the recess formed on the main surface, and the diaphragm having the wiring and the strain gauge face the recess. A semiconductor pressure sensor provided with a second substrate provided, and the opening shape of the recess is a polygonal shape having an obtuse angle portion when viewed from above, so that the thermal oxide insulating layer is prevented from rising and sealed It is possible to avoid the bonding failure of the substrates according to the above.

  Further, according to the semiconductor pressure sensor of the present invention, the first substrate having the thermal oxidation insulating layer on the main surface and the inner surface of the recess formed on the main surface, and the diaphragm having the wiring and the strain gauge face the recess. A semiconductor pressure sensor provided with a provided second substrate, wherein the corner formed by the main surface and the inner wall surface of the recess has a chamfered shape. It is possible to avoid the bonding failure of the substrates related to stopping.

It is a top view of the semiconductor pressure sensor of Embodiment 1 of this invention. It is sectional drawing which follows the AA line of the semiconductor pressure sensor of Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing process of the semiconductor pressure sensor of Embodiment 1 of this invention. It is a top view of the semiconductor pressure sensor of Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing process of the semiconductor pressure sensor of Embodiment 2 of this invention. It is sectional drawing of the semiconductor pressure sensor of Embodiment 3 of this invention. It is sectional drawing which shows the manufacturing process of the semiconductor pressure sensor of Embodiment 3 of this invention. It is a top view of the photomask for semiconductor pressure sensors of Embodiment 3 of this invention. It is a top view of the conventional semiconductor pressure sensor. It is sectional drawing which follows the CC line of the conventional semiconductor pressure sensor. It is sectional drawing which follows the DD line | wire of the conventional semiconductor pressure sensor.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
First, the configuration of the semiconductor pressure sensor according to Embodiment 1 of the present invention will be described. FIG. 1 is a top view showing a configuration of a semiconductor pressure sensor 100 according to Embodiment 1 of the present invention. 2 is a cross-sectional view taken along line AA in FIG.

  The semiconductor pressure sensor 100 includes a first semiconductor substrate 1, a recess 4 formed in the first semiconductor substrate 1, a second semiconductor substrate 2 that covers the recess 4 and is bonded to the first semiconductor substrate 1. Is provided. The first semiconductor substrate 1 and the second semiconductor substrate 2 are bonded via a thermal oxidation insulating layer 3. A strain (stress) gauge 5 is formed on the second semiconductor substrate 2, and an electrical wiring 7 is connected to the strain gauge 5 via an insulating film 6. FIG. 1 shows a state in which the insulating film 6 and the electric wiring 7 formed on the main surface 2a side of the second semiconductor substrate 2 are removed for easy understanding.

The configuration of the semiconductor pressure sensor 100 will be described in more detail.
The first semiconductor substrate 1 is a semiconductor substrate having a main surface (also referred to as a front surface) 1a and a back surface 1b, and a recess 4 is formed on the main surface 1a side. The surface of the first semiconductor substrate 1 in which the recess 4 is formed is covered with a thermal oxidation insulating layer 3. That is, the thermal oxidation insulating layer 3 is also formed on the inner surface of the recess 4. The first semiconductor substrate 1 is made of, for example, a silicon substrate. The silicon forming the first semiconductor substrate 1 may be single crystal silicon, but is not particularly limited thereto, and may be polycrystalline or amorphous. The thermal oxidation insulating layer 3 may be made of any material as long as it has insulating properties. However, in the present embodiment, since the first semiconductor substrate 1 is a silicon substrate, the thermal oxidation insulating layer 3 is used. Consists of a silicon oxide film.

  The shape of the recess 4 viewed from the main surface 1a side, that is, the opening shape of the recess 4 in a top view is a rectangular shape as shown by a thin broken line in FIG. 1, and its four corners (also referred to as corners) are not right angles, Has roundness. A portion surrounded by a thick broken circle in FIG. 1 is a rounded corner 4a.

  The second semiconductor substrate 2 is a semiconductor substrate having a main surface 2a and a back surface 2b, and the back surface 2b of the second semiconductor substrate 2 is formed on the main surface 1a of the first semiconductor substrate 1 with a thermal oxidation insulator. It is in contact with layer 3. The second semiconductor substrate 2 is laminated on the first semiconductor substrate 1 so as to cover the opening of the recess 4, and the back surface 2 b of the second semiconductor substrate 2 and the main of the first semiconductor substrate 1. The surface 1a is joined via the thermal oxide insulator layer 3. The second semiconductor substrate 2 is made of, for example, a silicon substrate. The silicon forming the second semiconductor substrate 2 may be single crystal silicon, but is not particularly limited thereto, and may be polycrystalline or amorphous.

  The portion of the second semiconductor substrate 2 that faces the recess 4, that is, the second semiconductor substrate 2 that is a thin plate covering the recess 4 constitutes a pressure receiving portion (diaphragm) 10 of the semiconductor pressure sensor 100. The thickness of the second semiconductor substrate 2 is, for example, 10 μm or more and 30 μm or less, but is not limited thereto.

  A pressure reference chamber 11 is constituted by the recess 4 formed in the second semiconductor substrate 2 and the second semiconductor substrate 2 covering the recess 4. In the case of an absolute pressure type pressure sensor (absolute pressure sensor), the pressure reference chamber 11 is sealed in a vacuum state.

  A strain gauge 5 is provided on the main surface 2 a side of the second semiconductor substrate 2. The strain gauge 5 is formed in the pressure receiving portion 10 that overlaps the concave portion 4 of the second semiconductor substrate 2 when viewed from the stacking direction of the first semiconductor substrate 1 and the second semiconductor substrate 2. The strain gauge 5 detects strain of the second semiconductor substrate 2 through deformation of the pressure receiving unit 10. As the strain gauge 5, for example, a p layer of a pn diode formed on an n-type silicon substrate is used. Further, by forming the strain gauge 5 near the outer periphery of the pressure receiving portion 10, high sensitivity can be obtained as a pressure sensor.

  An insulating film 6 is further formed on the main surface 2 a side of the second semiconductor substrate 2, and an electrical wiring 7 is formed on the insulating film 6. Specifically, the wiring groove of the insulating film 6 is provided at a position corresponding to the strain gauge 5, and the electric wiring 7 is formed so as to fill the wiring groove of the insulating film 6, thereby connecting to the strain gauge 5. The electrical wiring 7 is formed. With the electrical wiring 7 formed in this way, the resistance change of the strain gauge 5 when the pressure receiving portion 10 is deformed is taken out as an electrical signal.

Next, the manufacturing method of the semiconductor pressure sensor 100 of Embodiment 1 of this invention is demonstrated using FIG.
First, as shown in FIG. 3A, a thermally oxidized insulating layer 8 made of silicon oxide is formed on the surface of the first semiconductor substrate 1 made of, for example, single crystal silicon by a thermal oxidation method (step 1). In the thermal oxidation method, for example, the first semiconductor substrate 1 made of single crystal silicon is heated to about 1000 ° C. in an atmosphere containing moisture, and the silicon is oxidized to form the bottom surface of the first semiconductor substrate 1. A silicon oxide film is formed.
At least the main surface 1a of the first semiconductor substrate 1 is preferably polished so that the surface roughness (arithmetic average roughness) Ra is 1 nm or less before forming the thermal oxide insulating layer 8.

  Next, as shown in FIG. 3B, the thermally oxidized insulating layer 8 formed on the main surface 1a of the first semiconductor substrate 1 is partially removed to form an opening 9 (step 2). . The planar shape when the opening 9 is viewed from the main surface 1a side is a rectangular shape with rounded corners. The opening 9 is formed with micrometer accuracy by using a photoengraving technique. The removal of the thermal oxidation insulating layer 8 may be performed by wet etching with hydrofluoric acid, a mixed liquid of hydrofluoric acid and ammonium fluoride, or CF4 (carbon tetrafluoride) gas and oxygen gas, for example. May be performed by plasma etching. Etching is advanced until the thermal oxidation insulating layer 8 in a predetermined region is completely removed.

  As shown in FIG. 3C, the first semiconductor substrate 1 is etched using the thermal oxidation insulating layer 8 having a rectangular opening 9 having rounded corners as a mask when viewed from above. A recess 4 is formed in the main surface 1a of the semiconductor substrate 1 (step 3). As an etching method, for example, a method of etching in plasma while alternately switching between C4F8 (perfluorocyclobutane) gas and SF6 (sulfur hexafluoride) gas is applied. Alternatively, a method of etching in plasma using a mixed gas of SF6 gas and oxygen gas may be applied. Organic substances, impurities, etc. adhering to the first semiconductor substrate 1 during the etching are removed by sulfuric acid / hydrogen peroxide cleaning, ammonia / hydrogen peroxide cleaning, hydrochloric acid / hydrogen peroxide cleaning, or the like. As the dimension of the recess 4, it is sufficient that one side of the opening has a length of about 10 μm to 1000 μm.

  Next, as shown in FIG. 3D, all of the thermal oxide insulating layer 8 on the surface of the first semiconductor substrate 1 in which the recesses 4 are formed is removed (step 4). As a method for removing the thermal oxide insulating layer 8, wet etching using hydrofluoric acid or a mixed liquid of hydrofluoric acid and ammonium fluoride is preferable because a plurality of substrates can be processed at once.

  Thereafter, as shown in FIG. 3E, a thermal oxidation insulating layer 3 of silicon oxide is formed on the surface of the first semiconductor substrate 1 by using the same thermal oxidation method as in step 1 (step 5). Since the thermal oxidation insulating layer 3 is formed on the surface exposed to the outside of the first semiconductor substrate 1, it is formed on the inner surface (bottom surface and inner surface) of the recess 4 formed in the main surface 1a of the first semiconductor substrate 1. Is also formed.

The thermal oxide insulating layer 3 can also be formed using a vapor deposition method such as plasma CVD (Chemical Vapor Deposition). However, since the surface of the thermal oxidation insulating layer 3 formed by the vapor deposition method is rough, a bonding failure occurs in the subsequent step of bonding the second semiconductor substrate 2 to the first semiconductor substrate 1. Therefore, in the present invention, it is necessary to form the thermally oxidized insulating layer 3 by using a thermal oxidation method that is highly dense and can form a film suitable for bonding.
Further, before forming the thermal oxide insulating layer 8, the surface roughness (arithmetic average roughness) Ra of the main surface 1a of the first semiconductor substrate 1 and the back surface 2b of the second semiconductor substrate 2 is 1 nm or less. It is preferable to polish in advance.

  Next, as shown in FIG. 3F, the second semiconductor substrate 2 is laminated and bonded to the main surface 1a of the first semiconductor substrate 1 so as to cover the recess 4 (step 6). The second semiconductor substrate 2 is made of, for example, single crystal silicon, and the pressure reference chamber 11 is formed by the recess 4 of the first semiconductor substrate 1 and the second semiconductor substrate 2.

  The bonding method will be described in detail. First, in vacuum at room temperature, the second semiconductor substrate 2 is laminated so as to cover the opening of the recess 4 formed in the main surface 1a of the first semiconductor substrate 1, and the second semiconductor substrate 2 is attached to the first semiconductor substrate 2. Temporary bonding for temporarily fixing to the semiconductor substrate 1 is performed. Next, heat treatment is performed in a state where the first semiconductor substrate 1 and the second semiconductor substrate 2 are temporarily fixed. As a result, the second semiconductor substrate 2 is bonded to the first semiconductor substrate 1. The heat treatment for bonding the first semiconductor substrate 1 and the second semiconductor substrate 2 is performed in a temperature range of 900 ° C. or higher and 1100 ° C. or lower. By this heat treatment, the bonding strength of the bonding surface between the first semiconductor substrate 1 and the second semiconductor substrate 2 is improved to the same level as the base material. This heat treatment is performed in a nitrogen atmosphere or in a vacuum state.

The main surface of the first semiconductor substrate 1 is a liquid in which sulfuric acid and hydrogen peroxide are mixed at a volume ratio of 4: 1 immediately before bonding the first semiconductor substrate 1 and the second semiconductor substrate 2 together. It is preferable to wash la. Thereby, the defect at the time of bonding can be reduced.
For the second semiconductor substrate 2 as well, it is preferable to clean the back surface 2b of the second semiconductor substrate with a liquid in which sulfuric acid and hydrogen peroxide are mixed at a volume ratio of 4: 1 immediately before bonding. . This makes it possible to remove contaminants on the joint surface and make the joint surface hydrophilic, so that temporary bonding at room temperature is facilitated.

  Next, as shown in FIG. 3G, the second semiconductor substrate 2 is processed to be thinned to a desired thickness (step 7). As the processing method, grinding using a diamond wheel and chemical mechanical polishing using silica fine particles and an alkaline solution as finishing are used. The thickness of the second semiconductor substrate 2 is affected by the pressure range of the semiconductor pressure sensor and the size of the pressure receiving unit 10. For example, when the pressure range is 1 atm and the size of one side of the rectangular pressure receiving portion 10 is 400 μm, the thickness of the second semiconductor substrate 2 is suitably about 15 μm. Through the above steps, the pressure receiving portion 10 that is a thin plate portion of the second semiconductor substrate 2 covering the concave portion 4 is formed.

  On the main surface 2a side of the second semiconductor substrate 2 processed so as to be thinned to a desired thickness, a strain gauge 5 for detecting the strain of the pressure receiving portion 10 is formed as shown in FIG. (Step 8). The strain gauge 5 is a pressure receiving portion 10 that is a portion overlapping the concave portion 4 when viewed from the stacking direction of the first semiconductor substrate 1 and the second semiconductor substrate 2, that is, from the main surface 2 a side of the second semiconductor substrate 2. Formed. The strain gauge 5 is formed, for example, by implanting an impurity of a second conductivity type opposite to the first conductivity type into the second semiconductor substrate 2 of the first conductivity type. More specifically, the strain gauge 5 is formed by injecting boron, which is a p-type impurity, into the second semiconductor substrate 2 made of an n-type silicon substrate.

  A method for forming the strain gauge 5 will be described in detail. A photosensitive resin is patterned on the main surface 2a of the second semiconductor substrate 2 by photolithography. Boron ions are implanted into the main surface 2a of the second semiconductor substrate 2 in a state masked by the patterned photosensitive resin, followed by activation heat treatment. This activation heat treatment is performed at a temperature of 900 ° C. or higher and 1000 ° C. or lower. The activation heat treatment time is set according to the depth of boron. In this manner, a p-type region is formed on the n-type silicon substrate. By applying a potential of about 3 to 10 V to the formed p layer, the p layer is electrically insulated from the n layer of the n-type silicon substrate. Thus, the p layer can be used as the strain gauge 5 having a piezoresistance effect. About the arrangement | positioning position of p layer, it is preferable to arrange | position in the area | region where stress becomes large. Therefore, for example, the p layer is preferably disposed in the vicinity of the outer periphery of the pressure receiving unit 10. That is, the strain gauge 5 is preferably formed at a position facing the outer edge of the recess 4 when viewed from the stacking direction of the first semiconductor substrate 1 and the second semiconductor substrate 2.

  Next, as shown in FIG. 3I, an insulating film 6 is formed on the main surface 2a of the second semiconductor substrate 2 on which the strain gauge 5 is formed (step 9). A part of the formed insulating film 6 is opened above the strain gauge 5 to form a wiring groove 6a. As the insulating film 6, for example, phosphorus-doped glass is suitable.

  Finally, as shown in FIG. 3J, electrical wiring (metal film) 7 is formed on the insulating film 6 of the second semiconductor substrate 2 (step 10). The electrical wiring 7 has, for example, aluminum as a main component. The electric wiring 7 is formed on the insulating film 6 and is formed so as to fill the wiring groove 6a. Thus, the electrical wiring 7 in contact with the strain gauge 5, that is, the electrical wiring 7 for taking out the resistance change in the strain gauge 5 as an electrical signal to the outside is formed.

  After the electrical wiring 7 is formed, heat treatment is performed to stably detect a change in resistance of the strain gauge 5 by reducing the contact resistance at the interface between the strain gauge 5 and the electrical wiring 7. In order to stabilize the contact resistance, it is necessary to reduce a silicon oxide film having a thickness of several nanometers formed at the boundary between the silicon layer on which the strain gauge 5 is formed and the metal film constituting the electric wiring 7. . The reduction treatment is performed by heat treatment in a hydrogen atmosphere. In the heat treatment, the hydrogen partial pressure at the end of the heat treatment is set to 0.4 atm or less. The end of the heat treatment is, for example, when the operation of the heater for heating the semiconductor pressure sensor 100 is finished in the chamber in which the heat treatment is performed. Further, not only at the end of the heat treatment, the hydrogen partial pressure during the heat treatment may always be 0.4 atm or less. From the viewpoint of promoting the reduction treatment, the heat treatment temperature is preferably 350 ° C. or higher, for example. Further, if the temperature of the heat treatment is too high, disconnection of the electric wiring 7 may occur due to the difference in the flow of the metal film constituting the electric wiring 7 and the thermal expansion coefficient. Therefore, the heat treatment temperature is preferably 450 ° C. or lower.

  Through the above manufacturing process, the semiconductor pressure sensor 100 according to the first embodiment of the present invention shown in FIGS. 1 and 2 is obtained.

  In step 3 shown in FIG. 3C, the first semiconductor substrate 1 made of silicon is formed by wet etching using a TMAH (tetramethylammonium hydroxide) solution or a KOH (potassium hydroxide) solution. Can be etched. However, since the wet etching is anisotropic etching depending on the crystal orientation of the semiconductor substrate 1, the first semiconductor substrate is maintained while maintaining the shape of the opening 9 formed in the step shown in FIG. It is difficult to etch 1 to a predetermined depth.

  On the other hand, in the case of plasma etching, the etching progress direction does not depend on the crystal orientation of the first semiconductor substrate 1, and the etching proceeds along the kinetic energy direction of the reactive gas in the plasma. Further, the direction of the kinetic energy of the reactive gas in the plasma can be controlled from the outside, such as by arranging a high-frequency power source at a position where a vertical electric field is applied to the first semiconductor substrate 1 in the plasma apparatus. .

  Therefore, in the semiconductor pressure sensor 100 according to the first embodiment of the present invention, the recess 4 is formed in the first semiconductor substrate 1 made of silicon by using plasma etching, so that it is formed in the thermally oxidized insulating layer 8. It is possible to form the concave portion 4 that maintains the shape of the opening 9, that is, a rectangular shape having rounded corners in the top view.

Next, functions and effects obtained by the semiconductor pressure sensor 100 according to the first embodiment of the present invention will be described.
When silicon is thermally oxidized to thermally oxidized silicon, its volume expands about 2.3 times. This value is derived by comparing silicon and silicon oxide in volume per mole. First, the density of silicon is 2.33 g / cm ³ , and the silicon mass corresponding to 1 mole is 28 g. Therefore, the volume per mole of silicon is obtained by the following equation.

Moreover, since the density of silicon oxide is 2.21 g / cm ³ and the mass of silicon oxide corresponding to 1 mol is 60 g, the volume per mol of silicon oxide can be obtained by the following equation.

Therefore, the volume of silicon oxide is about 2.3 times the volume of silicon.

  Therefore, when the thermal oxidation process is applied to the first semiconductor substrate 1 in the above-described step 5 in FIG. 3E, the above-described volume expansion occurs on the surface of the first semiconductor substrate 1, and the volume expansion is the first. 1 induces distortion of the surface of the semiconductor substrate 1. The distortion of the first semiconductor substrate 1 due to the volume expansion occurs both in the thickness direction of the first semiconductor substrate 1 and in the in-plane direction.

The strain in the thickness direction of the first semiconductor substrate 1 is evenly released on the main surface 1a side, the back surface 1b side, and the like of the first semiconductor substrate 1 that is free space. That is, the strain in the thickness direction of the first semiconductor substrate 1 on the main surface 1a of the first semiconductor substrate 1 is uniformly released on the main surface 1a side of the first semiconductor substrate 1 which is a free space.
On the other hand, strain in the in-plane direction of the first semiconductor substrate 1 spreads along the surface of the first semiconductor substrate 1 and concentrates on corners of the first semiconductor substrate 1 where strains gather from different directions. In particular, the strain concentrated on the opening end of the recess 4 provided on the main plane 1a side of the first semiconductor substrate 1 is large.

A case where the strain concentration of the semiconductor substrate due to the volume expansion of silicon occurs in the conventional semiconductor pressure sensor will be described with reference to FIGS.
FIG. 9 is a top view of a conventional semiconductor pressure sensor 400. FIG. 10A is a cross-sectional view of the first semiconductor substrate 401 constituting the semiconductor pressure sensor 400 of FIG. 9, taken along the line CC, and FIG. 10B is a first view shown in FIG. 2 is a cross-sectional view showing a state in which a second semiconductor substrate 2 is bonded to the semiconductor substrate 401 of FIG. A thermal oxide insulating layer 403 is formed on the surface of the first semiconductor substrate 401 shown in FIG. FIG. 9 shows a state in which the insulating film and the electric wiring on the second semiconductor substrate are removed for easy understanding.

  The opening shape of the concave portion 404 of the conventional semiconductor pressure sensor 400 in the top view is a quadrangular shape with corners at right angles 404a as shown by thin broken lines in FIG. A portion surrounded by a thick broken-line circle in FIG. 9 is a right-angled corner 404a. Thus, when the corners form a right angle, when the first semiconductor substrate 401 is viewed in a cross-section CC along the diagonal of the opening shape of the recess 404, as shown in FIG. Due to the strain concentrated on the opening end of the recess 404, the first semiconductor substrate 401 is raised upward.

  For this reason, as shown in FIG. 10B, the bulge caused by the strain concentrated on the corners of the quadrangular shape is such that the bonding surface is uniformly applied when the first semiconductor substrate 401 and the second semiconductor substrate 402 are bonded together. It inhibits and induces a bonding failure portion 412a surrounded by a dashed ellipse. Furthermore, even if it can join initially, there exists a problem on reliability that joining strength deteriorates by the thermal load in long-term use.

  On the other hand, in the semiconductor pressure sensor 100 according to the first embodiment of the present invention, the opening shape of the recess 4 formed in the main surface 1a of the first semiconductor substrate 1 has a rounded corner when viewed from above. It has a rectangular shape. Therefore, in the step of thermal oxidation treatment in which the thermal oxidation insulating layer 3 is formed on the surface of the first semiconductor substrate 1 after the formation of the recess 4, the planar strain concentrated on the corners of the opening of the recess 4 is dispersed. The upward bulging of the first semiconductor substrate 1 can be suppressed. As a result, it is possible to avoid poor bonding in the step of bonding the second semiconductor substrate 2 to the first semiconductor substrate 1 on which the thermal oxide insulating layer 3 is formed, and further, the vacuum state in the pressure reference chamber 11 is prolonged. It can be maintained over a period of time.

Embodiment 2. FIG.
A configuration of the semiconductor pressure sensor according to the second embodiment of the present invention will be described. FIG. 4A is a top view showing the configuration of the semiconductor pressure sensor 200 according to Embodiment 2 of the present invention. FIG.4 (b) is sectional drawing which follows the BB line of Fig.4 (a).
In this embodiment, the opening shape of the recess 204 formed in the main surface 201a of the first semiconductor substrate 201 in a top view is different from that in the first embodiment. Since the other configuration of the present embodiment is the same as that of the first embodiment described above, the same elements are denoted by the same reference numerals, and description thereof will not be repeated.

  The semiconductor pressure sensor 200 includes a first semiconductor substrate 201, a recess 204 formed in the first semiconductor substrate 201, a second semiconductor substrate 2 that covers the recess 204 and is bonded to the first semiconductor substrate 201. Is provided. The first semiconductor substrate 201 and the second semiconductor substrate 2 are bonded via a thermal oxidation insulating layer 203. A strain gauge 5 is formed on the second semiconductor substrate 2, and an electrical wiring 7 is connected to the strain gauge 5 via an insulating film 6. FIG. 4 shows a state in which the insulating film 6 and the electric wiring 7 formed on the main surface 2a side of the second semiconductor substrate 2 are removed for easy understanding.

  The shape of the opening of the recess 204 formed in the main surface 201a of the first semiconductor substrate 201 as viewed from the main surface 201a side of the first semiconductor substrate 201, that is, the shape of the opening in a top view is indicated by a thin broken line in FIG. Thus, it is a polygonal shape having obtuse corners. A portion surrounded by a thick dashed circle in FIG. 4 is an obtuse corner 204a. The surface of the first semiconductor substrate 201 in which the recess 204 is formed is covered with a thermal oxidation insulating layer 203. That is, the thermal oxidation insulating layer 203 is also formed on the inner surface of the recess 204. Other configurations are the same as those of the first embodiment.

Next, the manufacturing method of the semiconductor pressure sensor 200 of Embodiment 2 of this invention is demonstrated using FIG.
First, as in step 1 of the first embodiment, a thermal oxidation insulating layer 208 is formed on the surface of the first semiconductor substrate 201 made of single crystal silicon by a thermal oxidation method (see FIG. 5A).

  Next, as in step 2 of the first embodiment, the thermally oxidized insulating layer 208 formed on the main surface 201a of the first semiconductor substrate 201 is partially removed to form an opening 209 (FIG. 5). (See (b)). Unlike the first embodiment, the planar shape of the opening 209 when viewed from the main surface 201a side is a polygonal shape having obtuse corners.

  The first semiconductor substrate 201 is etched using the thermal oxidation insulating layer 208 having a polygonal opening 209 having an obtuse corner as viewed from above as a mask in the same manner as in step 3 of the first embodiment. A recess 204 is formed in the main surface 201a of one semiconductor substrate 201 (see FIG. 5C). The subsequent steps are the same as the manufacturing steps after step 4 described in the first embodiment, and the description thereof is omitted.

  In the semiconductor pressure sensor 200 configured as described above, the opening shape of the recess 204 formed in the main surface 201a of the first semiconductor substrate 201 is a polygonal shape having obtuse corners when viewed from above. . Therefore, in the thermal oxidation treatment step of forming the thermal oxidation insulating layer 203 on the surface of the first semiconductor substrate 201 after forming the recess 204, the strain in the planar direction concentrated on the corner of the opening of the recess 204 is dispersed. The upward bulging of the first semiconductor substrate 201 can be suppressed. As a result, as in the first embodiment, it is possible to avoid poor bonding in the process of bonding the second semiconductor substrate 2 to the first semiconductor substrate 201 on which the thermal oxide insulating layer 203 is formed, and further, the pressure reference It becomes possible to maintain the vacuum state in the chamber 11 for a long period of time.

Embodiment 3 FIG.
A configuration of the semiconductor pressure sensor according to the third embodiment of the present invention will be described. FIG. 6 is a cross-sectional view showing the configuration of the semiconductor pressure sensor 300 according to Embodiment 3 of the present invention, and is a cross-sectional view at a position corresponding to the line AA shown in FIG.
In this embodiment, the cross-sectional shape of the recess 304 formed in the main surface 301a of the first semiconductor substrate 301 is different from that in the first embodiment. Since the other configuration of the present embodiment is the same as that of the first embodiment described above, the same elements are denoted by the same reference numerals, and description thereof will not be repeated.

  The semiconductor pressure sensor 300 includes a first semiconductor substrate 301, a recess 304 formed in the first semiconductor substrate 301, a second semiconductor substrate 2 that covers the recess 304 and is bonded to the first semiconductor substrate 1. Is provided. The first semiconductor substrate 301 and the second semiconductor substrate 2 are bonded via a thermal oxidation insulating layer 303. A strain gauge 5 is formed on the second semiconductor substrate 2, and an electrical wiring 7 is connected to the strain gauge 5 via an insulating film 6.

  The recess 304 formed in the main surface 301a of the first semiconductor substrate 301 will be described in detail. The shape of the opening of the recess 304 viewed from the main surface 301a side of the first semiconductor substrate 301, that is, the opening shape of the recess 304 in a top view is a rectangular shape with rounded corners, as in the first embodiment. On the other hand, the shape of the recess 304 in the cross section perpendicular to the main surface 301a of the first semiconductor substrate 301 is formed by the main surface 301a of the first semiconductor substrate 301 and the inner wall surface of the recess 304, as shown in FIG. It is formed in a chamfered shape with the corners removed. That is, an inclined portion 304 a that is an inclined surface having an obtuse angle with the main surface 301 a is formed over the entire circumference of the opening end of the recess 304. A portion surrounded by a thick broken circle in FIG. 6 is an inclined portion 304a. A thermal oxide insulating layer 303 is also formed on the inclined portion 304a. Other configurations are the same as those of the first embodiment.

  Next, the manufacturing method of the semiconductor pressure sensor 300 of Embodiment 3 of this invention is demonstrated using FIG. The manufacturing method of the semiconductor pressure sensor 300 according to the third embodiment of the present invention differs from the other embodiments in the step of forming the recess 304.

  First, as in step 1 of the first embodiment, a thermal oxidation insulating layer 308 is formed on the surface of the first semiconductor substrate 301 made of single crystal silicon by a thermal oxidation method (see FIG. 7A).

  Next, a photosensitive resin 315 is applied to the main surface 301a of the first semiconductor substrate 301, and an exposure glass substrate 313 for photoengraving is disposed on the photosensitive resin 315 (see FIG. 7B). ).

  FIG. 8A is a top view of the exposure glass substrate 313, and FIG. 8B is an enlarged view of a region surrounded by a thin dashed square in FIG. 8A. Generally, in a glass substrate for exposure used in photolithography technology, a region where a pattern is left is masked with a chromium film that shields light during exposure. As shown in FIG. 8A, the glass substrate for exposure 313 used in Embodiment 3 is provided with an opening pattern 316 having a predetermined shape without a chromium film at the center, and is further adjacent to the outside of the opening pattern 316. A plurality of minute opening patterns 314 having the same shape without a chromium film are provided in the region. The opening pattern 316 has a rectangular shape with rounded corners. Further, the minute opening pattern 314 has a rectangular shape and moves away from the opening pattern 316 provided on the exposure glass substrate 313 toward the outside of the exposure glass substrate 313, that is, in the direction of the arrow in FIG. Along the arrangement, the arrangement density is reduced, and finally, the arrangement density is eliminated. A region where the density of the minute opening pattern 314 changes in this way is called a gray tone region. In the third embodiment of the present invention, as shown in FIG. 8A, the area between the two dashed lines around the opening pattern 316 provided in the exposure glass substrate 313 is a gray tone area. 313a. The size of the minute opening pattern 314 provided in the gray tone region 313a is preferably 1 μm or less.

  In FIG. 8B, the minute opening patterns 314 are all rectangular and have the same size, but may have different shapes and sizes. When the minute opening patterns 314 having different shapes and sizes are arranged, the opening ratio of the chromium film decreases from the periphery of the opening pattern 316 provided on the exposure glass substrate 313 toward the outside of the exposure glass substrate 313. , In the end to be zero.

  The photosensitive resin 315 is patterned by photolithography using the glass substrate for exposure 313 described above. First, when the photosensitive resin 315 formed on the thermal oxidation insulating layer 308 is exposed using the exposure glass substrate 313 as a photomask, light is transmitted through the opening pattern 316 and the minute opening pattern 314 of the exposure glass substrate 313. The underlying photosensitive resin 315 is exposed to light. Of the photosensitive resin 315, the sensitivity of the region corresponding to the gray tone region 313a is lower than the sensitivity of the region corresponding to the opening pattern 316, that is, the region completely irradiated with light. Accordingly, as shown in FIG. 7C, an opening 317 is formed in the photosensitive resin 315 by a development process after exposure, and the photosensitive resin 315 is not formed in a region corresponding to the gray tone region 313a in the opening 317. An inclined portion 315a is formed which gradually increases in thickness as it goes outward. Therefore, the opening 317 formed in the photosensitive resin 315 is formed in a shape in which the opening area becomes smaller as the first semiconductor substrate 301 is approached. The photosensitive resin 315 on which the inclined portion 315a is formed is also called a gray tone mask 315.

  Next, when the thermal oxide insulating layer 308 under the gray tone mask 315 is etched in the same manner as in step 2 of Embodiment 1, the opening 309 having the inclined portion 308a having the same thickness as the gray tone mask 315 is obtained. Is formed on the thermal oxide insulating layer 308 (see FIG. 7D). That is, the opening 309 formed in the thermal oxidation insulating layer 308 is formed in a shape in which the opening area becomes smaller as the distance from the first substrate is approached, similar to the opening 317 formed in the photosensitive resin 315.

  Using the thermally oxidized insulating layer 308 in which the opening 309 is formed as a mask, the first semiconductor substrate 301 made of silicon is etched in plasma as in step 3 of Embodiment 1 to form a recess 304. . In plasma etching, not only silicon but also the thermal oxide insulating layer 308 is etched to some extent. Until the silicon is etched to a desired depth, the inclined portion 308a of the thermal oxide insulating layer 308 disappears in accordance with the thickness inclination, and finally the first semiconductor substrate 301 made of underlying silicon is etched. . As a result, as shown in FIG. 6 (e), an inclined portion 304 a is formed at the opening end of the recess 304. Through the above steps, the first semiconductor substrate 301 is formed with a recess 304 having an inclined portion 304a at the opening end thereof. Since the subsequent steps are the same as those after step 5 described in the first embodiment, the description thereof is omitted.

Next, the effect obtained by the semiconductor pressure sensor 300 of Embodiment 3 of this invention is demonstrated using FIG.
FIG. 11A is a cross-sectional view at the position of the DD line passing through two opposite sides of the opening shape of the recess 404 of the first semiconductor substrate 401 constituting the semiconductor pressure sensor 400 of FIG. These are sectional drawings which show the state which joined the 2nd semiconductor substrate 2 to the 1st semiconductor substrate 401 shown to Fig.11 (a).

  As described in the first embodiment, when the opening shape of the recess in the top view is a square shape with a right corner as in the prior art, the distortion concentrates on the square corner. However, although it is small compared to the corners of the quadrangular shape, as shown in FIG. As shown in FIG. 11B, the bulge caused by the strain concentrated on one side of the rectangular shape also prevents the bonding surface from being uniformly applied when the first semiconductor substrate 401 and the second semiconductor substrate 402 are bonded to each other. In this case, a defective joint 412b surrounded by a dashed ellipse is induced.

  On the other hand, in the semiconductor pressure sensor 300 according to the third embodiment of the present invention, the opening of the recess 304 formed in the main surface 301a of the first semiconductor substrate 301 has a round corner at the top view. The rectangular shape is formed in a chamfered shape in which corners formed by the main surface 301a and the inner wall surface of the recess 304 are dropped. Therefore, in the step of thermal oxidation treatment in which the thermal oxidation insulating layer 303 is formed on the surface of the first semiconductor substrate 301 after the formation of the recess 304, it is concentrated on the corner and one side of the opening shape of the recess 304 in a top view. Distortion in the planar direction can be dispersed, and the upward protrusion of the first semiconductor substrate 301 can be further suppressed as compared with the first embodiment. As a result, it is possible to avoid poor bonding in the step of bonding the second semiconductor substrate 2 to the first semiconductor substrate 301 on which the thermal oxide insulating layer 303 is formed, and further, the vacuum state in the pressure reference chamber 11 is prolonged. It can be maintained over a period of time.

  In the third embodiment, the opening shape of the concave portion 304 in the top view may be a quadrangle with a square corner as in the conventional case. However, by making the opening shape a rectangular shape having rounded corners as described in Embodiment 1 and a polygonal shape in which the corners described in Embodiment 2 have an obtuse angle, one side portion and a corner portion of the opening shape Since the strain in the planar direction concentrated on the first semiconductor substrate 301 can be dispersed together, the effect of suppressing the upward bulging of the first semiconductor substrate 301 is greater than in the case of using the conventional opening shape.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is intended to include all modifications within the scope and meaning equivalent to the terms of the claims, which are indicated by the scope of the claims, not by the above description.

  DESCRIPTION OF SYMBOLS 1 1st semiconductor substrate, 1a main surface, 1b back surface, 2nd semiconductor substrate, 2a main surface, 2b back surface, 3 thermal oxidation insulating layer, 4 recessed part, 4a rounded four corners, 5 strain gauge, 6 insulation Membrane, 6a Wiring groove, 7 Electrical wiring, 8 Thermal oxidation insulating layer, 9 Opening portion, 10 Pressure receiving portion, 11 Pressure reference chamber, 12 Junction failure portion, 201 First semiconductor substrate, 201a Main plane, 203 Thermal oxidation insulating layer , 204 recess, 204a corner, 208 thermally oxidized insulating layer, 209 opening, 301 first semiconductor substrate, 301a main surface, 303 thermally oxidized insulating layer, 304 recessed, 304a inclined portion, 308 thermally oxidized insulating layer, 308a inclined Part, 309 opening part, 313 glass substrate for exposure, 313a gray tone region, 314 minute opening pattern, 315 photosensitive resin, 315a inclined part, 316 opening pattern, 317 opening, 401 first semiconductor substrate, 401a main surface, 404 recess, 404a corner, 412a poor bonding portion, 412b poor bonding portion.

Claims (7)

A first substrate having a thermal oxidation insulating layer on a main surface and an inner surface of a recess formed in the main surface;
A semiconductor pressure sensor comprising: a second substrate provided with a diaphragm having a wiring and a strain gauge facing the concave portion;
An opening shape of the concave portion is a rectangular shape having round corners as viewed from above. A first substrate having a thermal oxidation insulating layer on a main surface and an inner surface of a recess formed in the main surface;
A semiconductor pressure sensor comprising: a second substrate provided with a diaphragm having a wiring and a strain gauge facing the concave portion;
An opening shape of the concave portion is a polygonal shape having an obtuse corner when viewed from above, and a semiconductor pressure sensor. A first substrate having a thermal oxidation insulating layer on a main surface and an inner surface of a recess formed in the main surface;
A semiconductor pressure sensor comprising: a second substrate provided with a diaphragm having a wiring and a strain gauge facing the concave portion;
A corner portion formed by the main surface and the inner wall surface of the recess has a chamfered shape. A mask process for forming a mask having a rectangular opening with rounded corners in a top view on the main surface of the first substrate;
An etching step of forming a recess in the first substrate using the mask;
A film forming step of forming a thermal oxidation insulating layer on the main surface of the first substrate and the inner surface of the recess;
A laminating step of laminating a second substrate over the recess on the main surface of the first substrate to form a diaphragm;
An element forming step of forming a strain gauge on the diaphragm;
A method of manufacturing a semiconductor pressure sensor, comprising: a wiring step of forming a wiring connected to the strain gauge. A mask process for forming a mask having a polygonal opening having an obtuse corner on the main surface of the first substrate;
An etching step of forming a recess in the first substrate using the mask;
A film forming step of forming a thermal oxidation insulating layer on the main surface of the first substrate and the inner surface of the recess;
A laminating step of laminating a second substrate over the recess on the main surface of the first substrate to form a diaphragm;
An element forming step of forming a strain gauge on the diaphragm;
A method of manufacturing a semiconductor pressure sensor, comprising: a wiring step of forming a wiring connected to the strain gauge. A mask process for forming a mask having an opening having a shape in which an opening area is reduced as it approaches the first substrate on the main surface of the first substrate;
An etching step of forming a recess in the first substrate using the mask;
A film forming step of forming a thermal oxidation insulating layer on the main surface of the first substrate and the inner surface of the recess;
A laminating step of laminating a second substrate over the recess on the main surface of the first substrate to form a diaphragm;
An element forming step of forming a strain gauge on the diaphragm;
A method of manufacturing a semiconductor pressure sensor, comprising: a wiring step of forming a wiring connected to the strain gauge. The mask used in the mask process is a photomask having an opening pattern of a predetermined shape and a plurality of minute opening patterns arranged so that the density decreases in a region adjacent to the outside of the opening pattern as the distance from the opening pattern decreases. The method of manufacturing a semiconductor pressure sensor according to claim 6, wherein the method is formed.

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