JP2010281570A - Semiconductor pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a semiconductor pressure sensor the diaphragm of which includes a high pressure resistance limit. <P>SOLUTION: The semiconductor pressure sensor includes a constitution wherein a cavity 20 is formed in a second silicon substrate 12 of an SOI substrate 10 and wherein the diaphragm 21 is formed by a first silicon substrate 14 and a base substrate 31 is joined to the second silicon substrate 12 forming the cavity 20. In the interface between the second silicon substrate 12 forming the cavity 20 and the base substrate 31, a tapered surface 13b is so formed as to provide an aperture. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a diaphragm type semiconductor pressure sensor that measures pressure such as atmospheric pressure.

  2. Description of the Related Art Conventionally, a diaphragm type semiconductor pressure sensor is known as a semiconductor pressure sensor for measuring tire pressures of automobiles (Patent Document 1).

  A cross-sectional structure of a conventional semiconductor pressure sensor is shown in FIG. In this semiconductor pressure sensor, a first silicon substrate 111 and a second silicon substrate 113 are stacked with an oxide film 112 interposed therebetween, and the piezoelectric element 103 is formed on the first silicon substrate 111 so as to form a bridge circuit. A semiconductor substrate 110 made of an SOI (Silicon On Insulator) substrate is used. In this semiconductor substrate 110, a laminated film made of a photoresist or the like is formed on the surface (lower surface in the figure) of the second silicon substrate 113, and the concave portion 122 is formed by dry etching the second silicon substrate 113 using this laminated film as a mask. To do. Thereafter, the laminated film is removed by wet etching, and the glass substrate 115 is bonded to the surface of the semiconductor substrate 110 so as to close the recess 122, and the recess 122 is maintained in a vacuum state.

  The diaphragm 121 is formed in a rectangular shape in plan view so that the piezo element 103 is placed on each side of the diaphragm 121, and the piezo element 103 is wired so as to form a bridge circuit. Is output as a pressure measurement voltage.

In the conventional semiconductor pressure sensor, the bonding interface between the second silicon substrate 113 and the glass substrate 115 is entirely bonded. With this configuration, when pressure is applied to the diaphragm 121, the diaphragm 121 is recessed into the recess 122, but the second silicon substrate 113 and the like that form the recess 122 are not deformed. However, if a pressure exceeding the bending limit of the diaphragm 121 is applied, the bending stress is concentrated on the boundary portion between the diaphragm 121 and the second silicon substrate 113, the over-etched portion 113a, etc., so that the diaphragm 121 may be damaged. was there. Thus, a semiconductor pressure sensor is proposed in which a mechanical stopper is provided so that the diaphragm 121 does not bend beyond the bending limit (Patent Document 2).
JP 2001-358345 A JP-A-11-142269

  However, the conventional semiconductor pressure sensor that restricts the deformation of the diaphragm with a mechanical stopper may cause the diaphragm to abut against the mechanical stopper when shock pressure is applied. It was not possible to measure whether pressure was applied. In addition, this conventional semiconductor pressure sensor has a problem that the shape and structure are complicated, and the manufacturing process becomes complicated.

  In view of the problems of the prior art, an object of the present invention is to obtain a semiconductor pressure sensor having a high withstand pressure limit of a diaphragm.

  According to the present invention for achieving such an object, a cavity is formed in one silicon substrate of two bonded silicon substrates, a diaphragm is formed by the other silicon substrate, and one silicon substrate forming the cavity is formed in one silicon substrate. A semiconductor pressure sensor to which a base substrate is bonded, characterized in that a gap is formed at the bonding interface between the one silicon substrate forming the cavity and the base substrate.

In practice, the gap is formed over the entire circumference of the bonding interface between the one silicon substrate and the base substrate so as to surround the cavity.
The gap is preferably a tapered surface formed in the one silicon substrate and having a gap extending from the base substrate toward the cavity.

  In the semiconductor sensor of the present invention, an SOI substrate bonded with a thermal oxide film sandwiched between the two silicon substrates is used as the two silicon substrates, a cavity is formed in one silicon substrate, and a diaphragm is formed by the other silicon substrate and the thermal oxide film. It is suitable that the base substrate is bonded to the one silicon substrate.

  In practice, a sensitive resistance element is formed on the outer surface of the diaphragm portion of the SOI substrate along the outline of the diaphragm so as to form a bridge circuit. The sensitive resistor element is preferably a piezo element whose resistance value changes according to the distortion of the diaphragm.

  According to the present invention having the above configuration, when the pressure applied to the diaphragm increases, one of the silicon substrates starts to deform in a direction in which the gap between the gap and the base substrate becomes narrow, so that the bending stress of the diaphragm is reduced. Dispersion increases the pressure limit of the diaphragm. In addition, since one silicon substrate does not deform until a predetermined pressure, accurate pressure measurement is possible within a predetermined pressure range, and it is also possible to measure a pressure higher than a predetermined pressure at which the one silicon substrate and the base substrate are deformed. Become.

  The best mode for carrying out the present invention will be described with reference to the accompanying drawings. 1 is a cross-sectional view showing a main part of an embodiment of the present invention relating to a diaphragm type semiconductor pressure sensor, taken along a cutting line II in FIG. 2, and FIG. 2 is a plan view showing the main part of the semiconductor pressure sensor; FIG. 3 is a process diagram showing a manufacturing process of the semiconductor pressure sensor.

First, an SOI (silicon-on-insulator) substrate 10 on which the piezo element 22, the wiring 23, and the pad 24 are formed is prepared. The SOI substrate 10 includes a first silicon substrate 11 and the second silicon substrate 13 are bonded together via a silicon oxide film (Si0 ₂₎ 12 is an oxide film. A silicon oxide film 14, which is a thermal oxide film, is formed on the circuit surface (upper side surface) of the first silicon substrate 11. As a sensitive resistance element, a bridge circuit is formed under the silicon oxide film 14. Of the piezoelectric element 22, the wiring 23 and the pad 24 that are electrically connected to the piezoelectric element 22, and the silicon nitride Si ₃ N ₄ that insulates and protects the piezoelectric element 22, the wiring 23, and the silicon oxide film 14. A passivation film 15 is formed. Each pad 24 is exposed from the passivation film 15.

  In the SOI substrate 10, a cavity (concave portion) 20 is formed on the second silicon substrate 13 from the surface side, and the silicon oxide film 12, the first silicon substrate 11, and the silicon oxide film 14 that constitute the upper surface of the cavity 20. A diaphragm 21 is formed by the passivation film 15. The diaphragm 21 has a rectangular shape in plan view. The piezo element 22 is formed at a position on each side of the rectangular outline of the diaphragm 21.

  A round portion 12a is formed in the contour portion of the silicon oxide film 12b that constitutes the diaphragm 21 and faces the cavity 20. In the illustrated embodiment, since the silicon oxide film 12 and the second silicon substrate 13 are joined, the roundness 12a is formed similarly over the entire circumference of the silicon oxide film 12b.

  Furthermore, in this embodiment, a taper surface 13 b that is not bonded to the base substrate 31 and has a gap with the base substrate 31 is formed at the bonding interface between the second silicon substrate 13 that forms the diaphragm 21 and the base substrate 31. ing.

  Then, a base substrate 31 made of a glass substrate or a SiO substrate as a base substrate is bonded to the surface (lower surface) of the second silicon substrate 13, and the cavity 20 between the diaphragm 21 and the base substrate 31 is sealed, The inside of the cavity 20 is kept in a vacuum. The tapered surface 13b is not joined because there is a gap between it and the base substrate 31.

  When the diaphragm 21 is distorted according to the pressure applied to the outer surface, the resistance value of the piezo element 22 changes according to the distortion. The midpoint potential of the bridge circuit formed by the piezo element 22 is output as a sensor output to a known measuring device. Note that at least a part of the circuit of the measuring apparatus may be formed on the circuit surface of the SOI substrate 10.

  Next, a manufacturing method of this semiconductor pressure sensor will be described. FIG. 3A shows an SOI substrate 10 on which a piezo element 22, a wiring 23, and a passivation layer 15 are formed. The SOI substrate 10 at this stage is usually supplied in a wafer state.

  First, the surface of the second silicon substrate 13 serving as a bonding surface with the base substrate 31 is ground to form the second silicon substrate 13 with a predetermined thickness (FIG. 3B). This grinding process may be performed at the manufacturing stage of the SOI substrate 10.

  Next, a resist or the like is formed on the surface (lower surface) of the second silicon substrate 13 from below as an etching mask for forming the diaphragm 21. The resist film 16 can be formed by a normal process such as a coater. Subsequently, of the resist film 16 formed on the lower surface of the second silicon substrate 13, the resist film 16 corresponding to the region where the diaphragm 21 is to be formed is photopatterned to form a mask having a desired pattern (FIG. 3 (C)). In this embodiment, a pattern is formed in which a diaphragm 21 having a rectangular shape in plan view is formed.

Next, using the resist film 16 as a mask, the second silicon substrate 13 is dry-etched to dig the cavity 20 to form a diaphragm 21 (FIG. 3D). Here, the steps of isotropic etching and protective film formation are repeated from the surface (lower surface in the figure) side of the second silicon substrate 13 by a known Si-Deep Etcher used in a MEMS (Micro Electro Mechanical Systems) process. Then, the second silicon substrate 13 is dug to form the cavity 20. In Si-Deep Etcher, for example, two types of gases, C ₄ F ₈ and SF ₆ are used.

  When the etching of the second silicon substrate 13 proceeds and reaches the silicon oxide film 12, the silicon oxide film 12 serves as an etching stopper, and a cavity 20 having a rectangular shape in plan view is formed in the second silicon substrate 13. The silicon oxide film 12 is further etched to form a silicon oxide film 12b having a predetermined thickness. At this time, a cavity is formed at the boundary between the silicon oxide film 12b and the second silicon substrate 13 in the cavity 20. Roundness (R) 12 a is formed so as to go around 20. According to this dry etching process, the silicon oxide film 12 and the second silicon substrate 13 are etched while the above-described rounds 12a and 13a are formed, so that the silicon oxide film 12 is not over-etched.

  Since the inner wall surface (inner side surface) of the cavity 20 is formed at right angles to the diaphragm 21, the planar shape of the cavity 20 and the relative position with respect to the piezoelectric element 22 are kept constant regardless of the depth of the cavity 20. Can do.

  Through this dry etching process, a diaphragm 21 is formed by the silicon oxide film 12 b that becomes the upper surface of the cavity 20, the first silicon substrate 11, the silicon oxide film 14, and the passivation film 15.

  After the diaphragm 21 is formed, the entire resist film 16 as a mask is removed by, for example, known resist peeling (FIG. 3E). Even if this resist stripping step is performed, the roundness 12a of the silicon oxide film 12 is maintained.

  Next, a tapered surface 13b is formed by a CMP (Chemical Mechanical Polishing) process on the surface (lower surface) surrounding the cavity 20 of the second silicon substrate 13 from which the resist film 16 has been entirely removed (FIG. 3F). The tapered surface 13b may be formed by an ion milling process.

  Next, the base substrate 31 is bonded to the surface (lower surface) of the second silicon substrate 13 in a vacuum state (FIG. 3G). Since the taper surface 13b is separated from the base substrate 31, it is not joined and a gap is left. By this joining process, the cavity 20 between the diaphragm 21 and the base substrate 31 is sealed in a vacuum state, and an absolute pressure sensor structure is obtained. If necessary, the surface (lower surface) of the base substrate 31 is grinded to adjust its thickness.

  Then, finally, the wafer on which the SOI substrate 10 and the base substrate 31 are bonded is diced and cut into chips. Each divided chip becomes a semiconductor pressure sensor.

  In the semiconductor pressure sensor manufactured by the above process, when pressure is applied from the surface side of the first silicon substrate 11, the diaphragm 21 is distorted, and the resistance value of the piezo element 22 changes according to the distortion of the diaphragm 21. Thus, the midpoint potential of the bridge circuit changes. The pressure is measured by measuring the midpoint potential with a known measuring device and converting it with a predetermined conversion coefficient.

  When the pressure becomes equal to or higher than a predetermined pressure, the area of the cavity 20 on the diaphragm 21 side is reduced, that is, the second silicon substrate 13 is deformed in a direction in which the interval between the tapered surface 13b and the base substrate 31 is reduced. By this deformation, the stress generated by the pressure acting on the diaphragm 21 is dispersed, the tensile and bending stresses are reduced, and the diaphragm 21 is prevented from being damaged.

  As described above, according to the present embodiment, when a pressure within a predetermined range acts on the diaphragm 21, the diaphragm 21 is deformed and distorted, and an accurate pressure is measured by the piezo element 22 subjected to this distortion. Is done. When the pressure acting on the diaphragm 21 exceeds a predetermined value, the second silicon substrate 13 is deformed in the direction in which the interval between the tapered surface 13b and the base substrate 31 is narrowed as described above, and bending and tensile stress acting on the diaphragm 21 Is dispersed, so that the diaphragm 21 is prevented from being damaged. At this time, since the second silicon substrate 13 is deformed according to the pressure, it is possible to measure a pressure higher than a predetermined pressure and a pressure change.

  In the above embodiment, the gap at the bonding interface between the second silicon substrate 13 and the base substrate 31 is the tapered surface 13b. However, the sectional shape is not limited to the tapered surface, and may be a rectangle, an arc, or other shapes. .

  This embodiment is an absolute pressure sensor in which the cavity 20 is evacuated, but the present invention is a differential pressure or gauge pressure sensor in which a pressure introduction port is formed in the base substrate 31 and the cavity 20 communicates with the outside. It can also be applied to.

  In this embodiment, a piezo element is used as the sensitive resistance element. However, other elements may be used as long as the element can detect the distortion of the diaphragm 21. Further, the shape of the diaphragm 21 may be other shapes as long as it is distorted by receiving pressure, and the number and position of the sensitive resistance elements are not limited to the illustrated embodiment.

It is sectional drawing which shows the principal part of embodiment of the semiconductor pressure sensor to which this invention is applied along the cutting line II of FIG. It is a top view which shows the principal part of the semiconductor sensor. It is a figure which shows the state when a pressure is applied to the semiconductor pressure sensor. It is sectional drawing which shows the principal part by longitudinally cutting the conventional semiconductor pressure sensor.

Explanation of symbols

10 SOI substrate 11 First silicon substrate (the other silicon substrate)
12 Silicon oxide film (oxide film)
13 Second silicon substrate (one silicon substrate)
13b Tapered surface 14 Silicon oxide film 15 Passivation film 20 Cavity 21 Diaphragm 22 Piezo element (sensitive resistance element)
23 Wiring 31 Base substrate

Claims (6)

A cavity is formed in one silicon substrate of the two bonded silicon substrates, and a diaphragm is formed by the other silicon substrate,
A semiconductor pressure sensor in which a base substrate is bonded to one silicon substrate forming the cavity,
A semiconductor pressure sensor, wherein a gap is formed at a bonding interface between the one silicon substrate forming the cavity and a base substrate. 2. The semiconductor pressure sensor according to claim 1, wherein the gap is formed over the entire circumference of the bonding interface between the one silicon substrate and the base substrate so as to surround the cavity. 3. The semiconductor pressure sensor according to claim 1, wherein the gap is a tapered surface formed in the one silicon substrate and having a gap extending from the base substrate toward the inside of the cavity. 4. 4. The semiconductor sensor according to claim 1, wherein the two silicon substrates are SOI substrates bonded together with an oxide film interposed therebetween, and a cavity is formed in one silicon substrate and the other silicon substrate is bonded to the other silicon substrate. A semiconductor pressure sensor in which a diaphragm is formed by a substrate and an oxide film, and the base substrate is bonded to the one silicon substrate. 5. The semiconductor pressure sensor according to claim 4, wherein a sensitive resistance element is formed along an outline of the diaphragm so as to form a bridge circuit on an outer surface of the diaphragm portion of the SOI substrate. 6. The semiconductor pressure sensor according to claim 5, wherein the sensitive resistance element is a piezo element whose resistance value changes in accordance with distortion of the diaphragm.

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