JP4273438B2 - microphone - Google Patents

Description

The present invention relates to a microphone , and more particularly to a microphone provided with an element thin film such as a diaphragm.

  By applying semiconductor integrated circuit manufacturing technology, a vibration sensor has been developed in which a single crystal silicon or polycrystalline silicon is laminated on a silicon substrate to form a thin film, and this thin film is used as a diaphragm. A diaphragm made of silicon has less internal stress and a lower density than metals such as aluminum and titanium, so that a highly sensitive vibration sensor can be obtained and compatibility with a semiconductor integrated circuit manufacturing process is good. As a vibration sensor having such a diaphragm, there is a condenser microphone disclosed in Patent Document 1, for example. In this capacitor microphone, after forming a diaphragm (movable electrode) and a fixed electrode on the surface of a semiconductor substrate made of a single crystal silicon (100) surface, an etching mask is formed on the outer periphery of the back surface of the semiconductor substrate, The semiconductor substrate is etched from the back side to the surface, and a through hole is formed in the center of the semiconductor substrate. As a result, the periphery of the diaphragm is fixed to the surface of the semiconductor substrate, and the central portion is hollowly supported on the through hole, and can be vibrated by sound vibration or the like.

  However, in the capacitor microphone having such a structure, since the (100) plane semiconductor substrate is crystal-anisotropically etched from the back side, an inclined surface due to the (111) plane appears on the inner peripheral surface of the through hole. Is a truncated pyramid-shaped space that is greatly open on the back side. Therefore, the opening area on the back surface side of the through hole is larger than the area of the diaphragm, and it is difficult to reduce the size of the condenser microphone. If the thickness of the semiconductor substrate is reduced, the ratio of the opening area of the back surface to the opening area of the surface of the through hole can be reduced, but the handling of the semiconductor substrate becomes difficult because the strength of the semiconductor substrate is reduced, There is a limit to reducing the thickness of the semiconductor substrate.

  In the film type sensor described in Patent Document 2, a through hole is opened from the back surface side of the semiconductor substrate by vertical etching such as so-called DRIE (Deep Reactive Ion Etching) or ICP (Inductively Coupled Plasma). Therefore, it is possible to reduce the size of the membrane sensor by the amount that the through hole does not spread in a truncated pyramid shape. However, in apparatuses such as DRIE and ICP, the price of the apparatus is expensive and the wafer processing is in a single sheet form, so that productivity is poor.

  In addition, there is a method of crystal anisotropic etching of a semiconductor substrate from the surface side (diaphragm side), but in such a method, an etching hole has to be opened in the diaphragm, and sometimes the etching hole has a vibration characteristic of the diaphragm or There was a risk of adverse effects on strength, etc.

  As an etching method capable of forming a through hole in the substrate by crystal anisotropic etching of the (100) plane semiconductor substrate from the back side, and reducing the ratio of the opening area of the back surface to the opening area of the front surface, a patent is disclosed. There is a method described in Document 3. In this method, a sacrificial layer is first formed in a rectangular region to be opened on the surface of a silicon wafer, which is a semiconductor substrate, and a thin film made of silicon nitride is deposited on the sacrificial layer. It is sufficient that the through hole has a size that can reach the sacrificial layer by anisotropic etching.

  However, in this etching method, since the thin film is exposed to the etchant of the substrate when the substrate after etching the sacrificial layer on the surface is etched, it is not possible to use single crystal silicon or polycrystalline silicon as the material of the thin film. . In addition, since the thin film is formed directly on the substrate, it is difficult to incorporate a process or structure for improving the characteristics of the vibration sensor, such as stress control of the thin film and vent holes. Therefore, the etching method disclosed in Patent Document 3 is not suitable as a method for manufacturing a vibration sensor that requires high sensitivity such as a microphone.

JP-T-2004-506394 Special table 2003-530717 gazette JP-A-1-309384 JP 2006-157863 A

The present invention has been made in view of the technical problems as described above, and an object thereof is to provide a microphone that is small in size, high in productivity, and excellent in vibration characteristics.

The microphone of the present invention is resistant to a single semiconductor substrate made of single crystal silicon and having a through-hole penetrating the front and back surfaces and an etchant for etching the semiconductor substrate to form a through-hole. made of a material, the holding portion disposed on the surface of the semiconductor substrate is supported corners underside by the holding portion, and the element thin film covering the opening of the substrate surface side of the through hole, the surface of the semiconductor substrate And a back plate disposed so as to cover the element thin film with a gap therebetween, and a vent hole for communicating the surface side and the back side of the element thin film is formed between the holding portions. The area of the cross section formed and parallel to the substrate surface of the through hole gradually increases from the surface of the semiconductor substrate toward the back surface, and between the front surface and the back surface of the semiconductor substrate. It is characterized in that it turns from increase to decrease in this household.

According to the microphone of the present invention, the area of the cross section parallel to the substrate surface of the through hole formed in the single semiconductor substrate gradually increases from the front surface to the back surface of the semiconductor substrate, and Since the ratio has changed from increasing to decreasing in the middle between the front surface and the back surface, the ratio of the opening area of the through hole on the surface of the semiconductor substrate to the opening area of the through hole on the back surface can be made close to 1, thereby reducing the size of the microphone. be able to. In addition, since the volume of the through hole can be increased, acoustic compliance can be increased when the microphone is used as an acoustic sensor. In addition, since a vent hole for communicating the surface side and the back side of the element thin film is formed between the holding parts, a long vent hole can be formed, and when used for a microphone, etc. The acoustic resistance can be increased, and good acoustic characteristics can be obtained. Further, since the front surface side and the back surface side of the element thin film can be communicated with each other through the vent hole, the static pressure on the front and back surfaces of the element thin film can be balanced.

  In addition, the component demonstrated above of this invention can be combined arbitrarily as much as possible.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments.

(Embodiment 1)
FIG. 1A is a plan view showing the structure of a vibration sensor 11 according to Embodiment 1 of the present invention, and FIG. 1B is a sectional view thereof. The vibration sensor 11 is used for an acoustic sensor such as a semiconductor microphone or an ultrasonic sensor, a thin film filter, or the like. The vibration sensor 11 has a Si substrate 12 and an element thin film 13 (diaphragm). This Si substrate 12 is a (100) plane substrate. The Si substrate 12 is penetrated from the front and back by etching from the back side, and further, a rectangular through-hole 14 is provided in which the sides in the vertical and horizontal directions are along the (110) direction. In the through hole 14, inclined surfaces 15 and 17 are formed by a (111) plane or an equivalent crystal plane on the front surface side and the back surface side, and a vertical surface 16 is formed between the inclined surfaces 15 and 17. Here, the vertical plane 16 is actually composed of a plurality of crystal planes such as the (110) plane, the (311) plane, and the (411) plane, but is simply shown as a vertical plane. Therefore, the substrate cross section at the edge of the through hole 14 has a tapered shape on the front and back.

  The element thin film 13 is arranged on the upper surface of the Si substrate 12 so as to cover the opening on the surface side of the through hole 14, and the entire periphery of the lower surface is fixed to the upper surface of the Si substrate 12 by the holding portion 18. A narrow gap 19 is formed between the opening on the front surface side of the through hole 14 (or the surface that was the surface of the Si substrate 12) and the back surface of the element thin film 13 by the holding portion 18.

  In the case of the vibration sensor 11 having such a structure, although the through hole 14 is formed by etching the Si substrate 12 from the back side, the back side opening is smaller than the front side opening of the through hole 14. The area is not so large. Therefore, the area of the Si substrate 12 does not increase due to the through hole 14 as in the first conventional example. The Si substrate 12 need only be large enough to mount the element thin film 13 and, if necessary, circuit components, and the vibration sensor 11 can be miniaturized.

  Next, the manufacturing process of the vibration sensor 11 will be described with reference to FIGS. 2 (a) to 2 (d), FIGS. 3 (a) to 3 (d) and FIGS. 4 (a) to 4 (c). However, although a large number of vibration sensors 11 are manufactured on the wafer at a time, only one vibration sensor 11 is illustrated and described in the following description.

First, as shown in FIG. 2A, protective films 20 and 21 made of SiO ₂ are formed on the front and back surfaces of the (100) plane Si substrate 12 by a thermal oxidation method or the like. Next, the protective film 20 in the region where the gap 19 is to be formed is partially removed on the surface of the Si substrate 12 using a photolithography technique, and a rectangular etching window 22 is opened.

  A polycrystalline silicon thin film is formed on the surface of the Si substrate 12 from above the protective film 20, and the polycrystalline silicon thin film on the protective film 20 is removed using a photolithography technique. Thus, a rectangular sacrificial layer 23 made of a polycrystalline silicon thin film is formed on the surface of the Si substrate 12 in the etching window 22. The state at this time is shown in FIG.

Next, a protective film 24 made of SiO ₂ is formed on the surface of the Si substrate 12 from above the sacrificial layer 23, and the sacrificial layer 23 is covered with the protective film 24 as shown in FIG.

Next, a polycrystalline silicon thin film is formed on the protective film 24, and unnecessary portions of the polycrystalline silicon thin film are removed by using a photolithography technique. As shown in FIG. An element thin film 13 made of a crystalline silicon thin film is formed. Further, as shown in FIG. 3A, a rectangular protective film 25 made of SiO ₂ is formed on the element thin film 13, and the element thin film 13 is covered with the protective film 25.

  Thereafter, as shown in FIG. 3B, a part of the protective film 21 is partially removed on the back surface of the Si substrate 12 by using a photolithography technique, and a back surface etching window 26 is formed in the protective film 21 in a rectangular shape. Open. The back surface etching window 26 only needs to be large enough for crystal anisotropic etching starting from the back surface etching window 26 to reach the surface of the Si substrate 12. For example, if the Si substrate 12 has a thickness of 400 μm, one side is A relatively small backside etching window 26 of about 570 μm is sufficient. The vertical and horizontal sizes of the sacrificial layer 23 are determined by the required vertical and horizontal sizes of the element thin film 13, and for example, one side is about 650 μm.

  When the back surface etching window 26 is opened, etching is performed from the back surface etching window 26 by dipping in an etchant such as TMAH, KOH, or EDP (hereinafter referred to as an etchant such as TMAH). Etchant such as TMAH performs crystal anisotropic etching on Si. Therefore, on the back surface of the Si substrate 12, etching proceeds along the (111) plane and the equivalent crystal plane (inclined plane 17). A through-hole 14 having a truncated pyramid shape is formed on the back surface of the substrate 12.

When the through hole 14 reaches the surface of the Si substrate 12 in this way, the sacrificial layer 23 is exposed from the through hole 14 as shown in FIG. The protective films 20, 21, 24, and 25 made of SiO ₂ are not etched by an etchant such as TMAH, but the sacrificial layer 23 made of polycrystalline silicon is isotropically etched by an etchant such as TMAH. Therefore, when the sacrificial layer 23 is exposed in the through hole 14, as shown in FIG. 3D, the sacrificial layer 23 is etched from the exposed portion in the through hole 14 to the periphery, and the protective film 24 and Si A gap 19 is formed between the surface of the substrate 12.

  In this state, the element thin film 13 and the protective films 24 and 25 are floated from the surface of the Si substrate 12 by the gaps 19 and can function as thin films. However, since the gap 19 is a thin space, when the element thin film 13 and the protective films 24 and 25 vibrate, a damping effect occurs, which deteriorates vibration characteristics in a high frequency band and causes mechanical noise. In addition, the element thin film 13 and the protective films 24 and 25 are easily sticked to the Si substrate 12. In order to prevent these, the etching of the Si substrate 12 is further continued below the element thin film 13.

  Note that the thicker the gap 19 (sacrificial layer 23), the faster the etching rate. However, if the thickness is too thick, the sacrificial layer 23 takes a long time to be formed or the protective film 24 has poor coating properties. For this reason, the design is made in consideration of the above, for example, about 1 μm. On the other hand, the thickness of the element thin film 13 is designed in consideration of the trade-off between sensitivity and strength of the vibration sensor 11, and is set to about 1 μm, for example.

  When the gap 19 is formed between the protective film 24 and the surface of the Si substrate 12, the etchant enters the gap 19 and crystal anisotropically etches the Si substrate 12 from the surface side. In this anisotropic etching, etching proceeds in the direction indicated by the arrow in FIG. 4A, and the inclined surface 15 is formed in the through hole 14. Furthermore, since the etching rate is high at the tip of the edge of the through hole 14, the inner peripheral surface of the through hole 14 is rounded to form a vertical surface 16, and the through hole 14 is etched into a shape like a donut hole. The Thus, when the sacrificial layer 23 is completely removed by etching as shown in FIG. 4B, the Si substrate 12 is pulled up from the etchant.

After cleaning the Si substrate 12, the protective films 20, 21, 24, 25 made of SiO ₂ are etched with an HF aqueous solution or the like, and only the holding portion 18 by a part of the protective films 20, 24 as shown in FIG. Etching is terminated at the time when remains, and cleaning and drying are performed to complete the vibration sensor 11.

  If the vibration sensor 11 is manufactured in this manner, the through-hole 14 having a small spread on the back surface side can be opened only by etching from the back surface side of the Si substrate 12, and the vibration sensor 11 can be miniaturized. . Further, since the through-hole 14 can be opened only by etching from the back surface side, there is no need to open an etching hole in the element thin film 13, and the physical characteristics of the element thin film 13 in the vibration sensor 11 can be changed. The risk of reducing the strength of the thin film 13 is reduced.

  Further, the opening area on the back surface side of the through hole 14 is determined by the size of the back surface etching window 26 opened in the protective film 21, and the opening area on the surface side of the through hole 14 is determined by the size of the sacrificial layer 23. According to such a manufacturing method, the opening area of the through hole 14 can be accurately controlled.

  In the above embodiment, the sacrificial layer 23 is formed of polycrystalline silicon, but amorphous silicon may be used.

(Embodiment 2)
FIG. 5A is a plan view showing a vibration sensor 31 according to Embodiment 2 of the present invention, and FIG. 5B is a cross-sectional view thereof. In the vibration sensor 31, the element thin film 13 made of polycrystalline silicon is formed on the Si substrate 12 so as to cover the upper surface of the through hole 14. The element thin film 13 is supported on the lower surface of the outer peripheral portion by the holding unit 18 on the upper surface of the Si substrate 12 and floats from the upper surface of the Si substrate 12, and the region surrounded by the holding unit 18 can be deformed.

  6A to 6D and FIGS. 7A to 7D are cross-sectional views for explaining the manufacturing process of the vibration sensor 31. FIG. Hereinafter, the manufacturing process of the vibration sensor 31 will be described according to FIGS. 6A to 6D and FIGS. 7A to 7D.

First, after forming a SiO ₂ thin film on the upper surface of the Si substrate 12, unnecessary portions of the SiO ₂ thin film are removed by using a photolithography technique, and as shown in FIG. The sacrificial layer 32 made of a SiO ₂ thin film is formed only in the region where the 13 is to float.

  Next, a protective film 34 made of SiN is formed on the surface of the Si substrate 12 from above the sacrificial layer 32, and the sacrificial layer 32 is covered with the protective film 34 as shown in FIG. Next, as shown in FIG. 6C, an element thin film 13 made of polycrystalline silicon is formed on the surface of the protective film 34.

Further, as shown in FIG. 6D, a protective film 35 made of SiN is formed on the surface of the protective film 34 from above the element thin film 13, and the element thin film 13 is covered with the protective film 35. Further, a protective film 33 made of a material other than SiO ₂ is formed on the back surface of the Si substrate 12. At this time, if the protective film 33 is formed of a SiN thin film, the protective film 34 or the protective film 35 and the protective film 33 can be formed at the same time in the same process. When the protective film 33 is formed on the back surface of the Si substrate 12, as shown in FIG. 6D, a part of the protective film 33 is opened in a rectangular shape by using the photolithography technique, and the back surface etching window 26 is formed. . The back surface etching window 26 only needs to be large enough for the crystal anisotropic etching from the back surface etching window 26 to reach the surface of the Si substrate 12.

  When the back surface etching window 26 is opened, the Si substrate 12 is immersed in an etchant such as TMAH to etch the Si substrate 12 from the back surface etching window 26, and the through hole 14 is provided in the Si substrate 12. Etchant such as TMAH performs crystal anisotropic etching with respect to Si. Therefore, etching progresses along the (111) plane and the equivalent crystal plane on the back surface of the Si substrate 12, and finally FIG. ), The through hole 14 reaches the surface of the Si substrate 12 and the sacrificial layer 32 is exposed in the through hole 14.

Since the sacrificial layer 32 made of SiO ₂ is not etched by an etchant such as TMAH, the etching process is terminated when the sacrificial layer 32 is exposed, and the Si substrate 12 is cleaned.

Next, the Si substrate 12 is immersed in an HF aqueous solution. Although the HF aqueous solution does not attack the Si substrate 12, SiO ₂ is isotropically etched, so that the sacrificial layer 32 is moved from the exposed portion to the surroundings by the HF aqueous solution entering the through hole 14 from the back surface side of the Si substrate 12. As shown in FIG. 7B, a gap 19 is generated between the element thin film 13 and the surface of the Si substrate 12.

  After the sacrificial layer 32 is completely removed by etching, the Si substrate 12 is washed and then immersed in an etchant such as TMAH again. This etchant enters the gap 19 and crystal anisotropically etches the Si substrate 12 from the surface side. As a result, as in the case of the first embodiment, the corners of the Si substrate 12 are formed on the inner peripheral surface of the through hole 14 to form the inclined surface 15 and the vertical surface 16, and the through hole 14 has a shape like a donut hole. Is etched. In this way, when the desired through hole 14 is formed as shown in FIG. 7C, the Si substrate 12 is pulled up from the etchant and washed and dried. Finally, as shown in FIG. 7D, the protective films 33, 34, and 35 made of SiN are removed with a heated phosphoric acid aqueous solution or the like to complete the vibration sensor 31.

  If the vibration sensor 31 is manufactured in this manner, the through-hole 14 having a small spread on the back surface side can be opened only by etching from the back surface side of the Si substrate 12, and the vibration sensor 31 can be miniaturized. . Further, since the through-hole 14 can be opened only by etching from the back surface side, it is not necessary to open an etching hole in the element thin film 13, and the physical characteristics of the element thin film 13 in the vibration sensor 31 can be changed. The risk of reducing the strength of the thin film 13 is reduced.

  Further, the opening area on the back surface side of the through hole 14 is determined by the size of the back surface etching window 26 opened in the protective film 33, and the opening area on the front surface side of the through hole 14 is determined by the size of the sacrificial layer 32. According to such a manufacturing method, the opening area of the through hole 14 can be accurately controlled.

  Furthermore, since the etchant is switched between the step of crystal anisotropic etching of the through hole and the step of etching the sacrificial layer, there are less restrictions on selecting the etchant in each step. In addition, since there is no continuous transition from crystal anisotropic etching to isotropic etching, there is also an advantage that process management such as yield inspection can be performed in each etching process.

  In the case of the first embodiment, since the crystal anisotropic etching and the isotropic etching are performed by the same etchant, the crystal anisotropic etching and the isotropic etching can be continuously performed in the same apparatus. The work efficiency was high. On the other hand, in the case of the embodiment 2, since the crystal anisotropic etching and the isotropic etching are separate processes, the restrictions on the means for crystal anisotropic etching and the means for isotropic etching are reduced. For example, the isotropic etching may be chemical etching using a corrosive gas other than an aqueous solution.

(Embodiment 3)
FIG. 8A is a plan view showing the structure of the vibration sensor 41 according to Embodiment 3 of the present invention, and FIG. 8B is a cross-sectional view taken along the line XX of FIG. The vibration sensor 41 is a device in which the element thin film 13 is provided with functional parts such as a wrinkle structure and a stopper 43.

  The wrinkle structure of the element thin film 13 is composed of two bent portions 42 having a quadrangular ring shape. Each bent portion 42 is bent so that the cross section thereof protrudes toward the upper surface side of the element thin film 13. If a wrinkle structure is formed in the element thin film 13 in this way, the displacement of the element thin film 13 is increased or the bending due to the stress is reduced, as described in “The fabrication and use of micromachined corrugated silicon diaphragms” (JH Jerman, Sensors and Actuators A21-A23 pp.998-992, 1992).

  The stopper 43 is such that the surface of the element thin film 13 protrudes into a round projection. In the case of a capacitive vibration sensor (for example, a microphone described later), the element thin film 13 serves as a movable electrode, and a counter electrode (fixed electrode) is disposed on the upper surface of the element thin film 13. In the case of a capacitive vibration sensor, if the stopper 43 is provided on the upper surface of the element thin film 13, the vibration sensor 41 is brought into contact with the fixed electrode even when the element thin film 13 is greatly deformed. It is possible to prevent the element thin film 13 from being adsorbed to the counter electrode due to electrostatic force due to the electric charge of the electrode or capillary force due to moisture adhesion.

  FIGS. 9A and 9B, FIGS. 10A to 10D, FIGS. 11A and 11B, FIGS. 12A and 12B, and FIGS. 13A and 13B are the vibration sensors. It is a figure explaining the manufacturing process of 41. FIG. Hereinafter, the manufacturing process of the vibration sensor 41 will be described with reference to FIGS. First, as shown in FIGS. 9A and 9B, a sacrificial layer made of a polycrystalline silicon thin film is formed in a predetermined pattern on the surface of the Si substrate 12. The sacrificial layer includes a quadrangular sacrificial layer 44a located in the center, square sacrificial layers 44b and 44c formed in the formation region of the bent portion 42, a linear sacrificial layer 44d that connects the sacrificial layers 44a to 44c, and a stopper. The sacrificial layer 44e is formed in the formation region 43.

Next, as shown in FIG. 10A, the surface of the Si substrate 12 is covered with a protective film 45 made of SiO ₂ from above the sacrificial layers 44 a to 44 e, and the protective film 46 made of SiO ₂ is also formed on the back surface of the Si substrate 12. Form. At this time, since the protective film 45 is formed on the sacrificial layers 44a to 44e, the protective film 45 protrudes upward at the portions of the sacrificial layers 44a to 44e.

  As shown in FIG. 10B, an element thin film 13 made of a polycrystalline silicon thin film is formed on the protective film 45. Since the element thin film 13 is lifted by the sacrificial layers 44a to 44e via the protective film 45 in the regions of the sacrificial layers 44a to 44e, the bent portions 42 are formed on the sacrificial layers 44b and 44c, and the sacrificial layer 44e. A stopper 43 is formed on the top. Note that the element thin film 13 swells upward also on the sacrificial layers 44a and 44d to form protrusions 47 and 48.

Further, as shown in FIG. 10 (c), a protective film 49 made of SiO ₂ is formed on the surface of the protective film 45 from above the element thin film 13, and the element thin film 13 is covered with the protective film 49. A back side etching window 50 is opened in the protective film 46 on the back side.

  Thereafter, the Si substrate 12 is immersed in an etchant such as TMAH, and crystal anisotropic etching is performed from the back surface etching window 50 to form a through hole 14 having a truncated pyramid shape on the back surface of the Si substrate 12. The through hole 14 stops when etching on the lower surface of the Si substrate 12 reaches the edge of the back surface etching window 50.

  When the through hole 14 reaches the surface of the Si substrate 12, the sacrificial layer 44a is exposed to the through hole 14 as shown in FIG. When the sacrificial layer 44a is exposed, the sacrificial layer 44a is isotropically etched with an etchant such as TMAH. The isotropic etching thus started from the sacrificial layer 44a proceeds in the order of the sacrificial layer 44a → the sacrificial layer 44d → the sacrificial layer 44b → the sacrificial layer 44c, as indicated by thin line arrows in FIG. Then, when the etchant enters the gap after the sacrificial layers 44a to 44d are etched, FIGS. 11 (a) and 11 (b) and FIG. 12 (a) (FIG. 12 (a) represents the surface of the Si substrate 12). As indicated by thick arrows in FIG. 5, crystal anisotropic etching of the Si substrate 12 proceeds from the edge portions of the gaps 51a to 51d of the traces from which the sacrificial layers 44a to 44d have been removed, and the through holes 14 are also formed from the surface side of the Si substrate 12. Etching is performed.

  As a result, the upper surface of the Si substrate 12 is etched in a region inside the outer periphery of the sacrificial layer 44c, and the Si substrate 12 has a through hole 14 etched from the front surface side and the back surface side. At this time, the sacrificial layer 44e is removed by etching. Thus, when the through hole 14 is completely formed, the Si substrate 12 is pulled up from the etchant.

After the Si substrate 12 is cleaned, the protective films 45 and 49 made of SiO ₂ are removed by etching with an HF aqueous solution or the like, and held by the protective film 45 at the four corners of the element thin film 13 as shown in FIGS. Etching is terminated when only the portion 18 remains, and cleaning and drying are performed to complete the vibration sensor 41.

  Also in this embodiment, the through-hole 14 having a small spread on the back surface side can be opened only by etching from the back surface side of the Si substrate 12, and the vibration sensor 41 can be downsized. Further, since the through-hole 14 can be opened only by etching from the back surface side, it is not necessary to open an etching hole in the element thin film 13, and the physical characteristics of the element thin film 13 in the vibration sensor 41 can be changed. The risk of reducing the strength of the thin film 13 is reduced. Moreover, a wrinkle structure, a stopper, etc. can be easily formed in the element thin film 13 by the same process.

(Embodiment 4)
FIG. 14A is a plan view showing a structure of a vibration sensor 61 according to Embodiment 4 of the present invention, and FIG. 14B is a sectional view thereof. In the vibration sensor 11 of the first embodiment, the holding portion 18 is formed on the entire lower surface of the element thin film 13. However, in the vibration sensor 61 of the fourth embodiment, the holding portion 18 is provided only at the corners (four corners) of the element thin film 13. Forming. In the vibration sensor 61 of the fourth embodiment, since the holding portions 18 are provided only at the corner portions of the element thin film 13, the upper surface side and the lower surface of the element thin film 13 are passed through the vent holes 63 between the holding portions 18 of the element thin film 13 on the four sides. The side is in communication.

  FIG. 15A is a plan view showing the structure of another vibration sensor 62 according to Embodiment 4 of the present invention, and FIG. 15B is a sectional view thereof. In the vibration sensor 62, the holding portion 18 is formed only on one side of the element thin film 13. In the vibration sensor 62, the element thin film 13 is supported in a cantilever manner by the holding portion 18, so that the upper surface side and the lower surface side of the element thin film 13 communicate with each other through a vent hole 63 on three sides.

  In order to partially form the holding portion 18 like the vibration sensors 61 and 62, the width of the protective film is widened at the portion where the holding portion 18 is to be formed, or the distance from the etchant charging position (etching) If the distance from the start position to the end position) is increased, and part of the protective film is removed by managing the etching time and part of the protective film is left, the holding part 18 is moved by the remaining protective film. Can be formed. For example, in the vibration sensor 61, the holding portion 18 is formed at a position far from the center. In the vibration sensor 62, the width of the protective film on one side is made larger than the width of the protective film on the other three sides so that it remains after etching.

  Structures such as the vibration sensors 61 and 62 are desirable for use as a microphone (acoustic sensor). That is, in the vibration sensors 61 and 62, since the element thin film 13 is only partially fixed, the element thin film 13 becomes flexible and easily elastically deforms. Therefore, it is suitable for use as a microphone for detecting a dynamic pressure difference.

  In particular, when the element thin film 13 is rectangular, if only four corner portions of the element thin film 13 are fixed like the vibration sensor 61, the element thin film 13 becomes a flexible spring. Further, according to the fixing method of only the four corners, most of the element thin film 13 is deformed like a parallel plate, so that the sensitivity of the capacitance microphone is remarkably improved.

  The fixed portions at the four corners of the element thin film 13 are preferably formed in a shape extending diagonally so that external stress due to deformation does not concentrate. If the electrode pad 73 is connected to the extended portion, the electrode can be taken out from the element thin film 13 without inhibiting the vibration of the element thin film 13.

  Further, since the internal stress of the holding portion 18 affects the vibration characteristics of the element thin film 13, the vibration characteristics of the element thin film 13 can be changed by controlling the internal stress of the holding portion 18. For example, when the element thin film 13 has a strong tensile stress, the tensile stress of the element thin film 13 can be weakened and the sensitivity can be improved by making the holding portion 18 an oxide film having a compressive stress.

  Further, according to the structure such as the vibration sensors 61 and 62, since air permeability is provided between the surface of the Si substrate 12 and the element thin film 13, a static pressure difference can be eliminated on both sides of the element thin film 13. A vent hole function can be provided.

  In US Pat. No. 5,452,268, etc., the width of the vent hole in the planar direction is shortened in order to increase acoustic resistance. However, there is a limit in the process rule to narrow the width of the vent hole, and the effect cannot be expected so much.

The resistance component Rv of the vent hole is
Rv = (8 · μ · t · a ² ) / (Sv ² ) (Equation 1)
It is represented by Where μ is the friction loss coefficient of the vent hole, t is the length of the vent hole in the ventilation direction, a is the area of the diaphragm, and Sv is the sectional area of the vent hole. The roll-off frequency fL of the microphone (the limit frequency at which the sensitivity decreases) is
1 / fL = 2π · Rv (Cbc + Csp) (Expression 2)
It is represented by However, Rv is the resistance component of the above equation, Cbc is the acoustic compliance of the through hole 14, and Csp is the stiffness constant of the element thin film 13.

  In the vibration sensors 61 and 62, as shown in FIG. 16, the length t of the vent hole 63 between the upper surface of the Si substrate 12 and the element thin film 13 can be increased. Therefore, in the vibration sensors 61 and 62, as can be seen from the above (Equation 1), the acoustic resistance can be made extremely high by taking the length t of the vent hole 63, and it can be seen from the above (Equation 2). In addition, since the low frequency characteristics of the vibration sensors 61 and 62 can be improved, characteristics preferable as a microphone can be obtained.

The acoustic compliance (acoustic compliance of the back chamber) Ccav of the through hole 14 is
Ccav = Vbc / (ρc ² · Sbc) (Equation 3)
It is represented by Where Vbc is the volume of the through hole 14 (back chamber volume), ρc2 is the volume modulus of air, and Sbc is the area of the opening of the through hole 14.

  In the vibration sensors 61 and 62, the through-hole 14 having a smaller opening area than the volume can be formed by etching from both the front and back surfaces of the Si substrate 12. 14 can be made large, and even if the vent hole 63 is opened, the sensitivity can hardly be lowered.

  Further, as shown in FIG. 17A, after the crystal anisotropic etching is performed so that the central portion of the through hole 14 protrudes inward, the etching is continued, and the state shown in FIG. After that, the etching finally proceeds to a state as shown in FIG. 17C, and the etching of the through hole 14 is stopped when the (111) plane or an equivalent crystal plane appears. Therefore, if the etching is performed up to the state as shown in FIG. 17C, the volume of the through hole 14 is increased, and the acoustic compliance Ccav can be further increased. Alternatively, when etching from the state of FIG. 17A to the state of FIG. 17C, an appropriate volume of the through-hole 14 and vibration sensor size can be obtained by controlling the etching time.

  The state shown in FIG. 17C is the final form of crystal anisotropic etching, and the shape of the back chamber is determined by the size and relative position of the openings on the front and back surfaces. In the case of the final form, the shape of the back chamber (through hole 14) is kept almost constant even if the etching time is further increased, so that there is an advantage that the process stability is good and the yield is high.

  Next, the structure of a capacitance microphone 71 configured using the vibration sensor 61 having the above structure and a method for manufacturing the same will be described. 18A is a plan view of the microphone 71, FIG. 18B is a plan view of the microphone 71 (that is, the vibration sensor 61) with the back plate 72 removed, and FIG. 19 is a cross-sectional view of the microphone 71. The microphone 71 has a back plate 72 fixed on the vibration sensor 61 so as to cover the element thin film 13. The back plate 72 has a cap shape having a recess on the lower surface, and is fixed to the surface of the Si substrate 12 so that the element thin film 13 is accommodated in the recess. Further, a gap is formed between the lower surface of the back plate 72 and the element thin film 13 so as not to disturb the vibration of the element thin film 13.

  A metal electrode 73 is provided on the upper surface of the back plate 72. The metal electrode 73 is not provided on the entire surface of the back plate as shown in FIG. 18, but is provided on a part of the back plate 72, particularly on a part facing a relatively large amplitude part of the element thin film 13. This is to reduce the parasitic capacitance and improve the characteristics of the capacitive microphone 71. When the element thin film 13 is fixed at the four corners as in the present embodiment, if the shape of the metal electrode 73 is substantially octagonal as shown in FIG. 18A, the parasitic capacitance is reduced and limited. Can be used effectively. A plurality of acoustic holes 74 and 75 are opened in the metal electrode 73 and the back plate 72. Therefore, the acoustic vibration from above passes through the acoustic holes 74 and 75 of the metal electrode 73 and the back plate 72 and reaches the element thin film 13 to vibrate the element thin film 13. The element thin film 13 (movable electrode) made of polycrystalline silicon has conductivity, and the capacitance between the element thin film 13 and the metal electrode 73 (fixed electrode) changes when the element thin film 13 vibrates. Acoustic vibrations can be detected by taking them out as electrical signals through the electrode pads 76 on the element thin film 13 side and the electrode pads 77 on the back plate 72 side, and detecting the change in capacitance.

  Next, the manufacturing process of the microphone 71 will be described with reference to FIGS. 20 (a) to 20 (d) and FIGS. 21 (a) to 21 (d). First, as shown in FIG. 20A, a protective film 20, a sacrificial layer 23, a protective film 24, an element thin film 13, and a protective film 25 are sequentially stacked on the surface of the Si substrate 12, and protection is performed on the back surface of the Si substrate 12. A film 21 is formed. This is the same structure as that in FIG. 3A of the first embodiment, and is manufactured through the same steps as those in FIGS. 2A to 2D of the first embodiment.

  Next, as shown in FIG. 20B, a SiN film is formed from the surface of the protective film 25 to the outer peripheral surfaces of the protective films 24 and 25, and a back plate 72 is formed of the SiN film. Thereafter, as shown in FIG. 20C, an acoustic hole 75 is opened in the back plate 72 by etching. At this time, although not shown in FIG. 20, the SiN film in the electrode extraction portion is also etched. Next, as shown in FIG. 20 (d), a Cr film is formed on the surface of the back plate 72, Au is formed thereon to obtain an Au / Cr film, and then the Au / Cr film is formed into a predetermined shape. The metal electrode 73 and the electrode pads 76 and 77 are manufactured by etching.

  Next, a back surface etching window 26 is opened in the back surface protective film 21 using a photolithography technique. As for the size of the back surface etching window 26, a side of about 570 μm is sufficient for the (100) plane Si substrate 12 having a thickness of 400 μm. When the back surface etching window 26 is opened, the Si substrate 12 is dipped in an etchant such as TMAH, and the Si substrate 12 is crystal anisotropically etched from the back surface side, and the through hole 14 is opened in the Si substrate 12. This state is shown in FIG.

  As shown in FIG. 21 (a), when the sacrificial layer 23 is exposed in the through hole 14, the sacrificial layer 23 of polycrystalline silicon is isotropically etched by an etchant such as TMAH, as shown in FIG. 21 (b). A gap 19 is formed on the surface of the Si substrate 12. When the gap 19 is formed, an etchant such as TMAH enters the gap 19 to etch the Si substrate 12 from the surface side, and further the etching proceeds in the horizontal direction. As shown in FIG. 4, the cross-sectional shape is tapered on the front and back.

  When the desired shape of the through hole 14 is obtained, the Si substrate 12 is pulled up from the etchant. Then, the protective films 21, 24, and 25 that protect the element thin film 13 are etched with an HF aqueous solution or the like to remove the protective film 20 and the holding portion 18 on the lower surface of the back plate 72. At this time, the protective film 25 is etched with an HF aqueous solution mainly entering from the acoustic holes 74 and 75. Therefore, it is desirable that the arrangement intervals of the acoustic holes 74 and 75 are substantially equal so that the etching is performed uniformly as shown in FIG. Here, if the arrangement interval is reduced, the etching time can be shortened. However, the number of acoustic holes 74 and 75 is increased accordingly, and the electrode area is reduced and the sensitivity is reduced. Also, the arrangement interval of the acoustic holes is related to the size of the holding portion 18. That is, if the arrangement interval is too large, the etching time becomes long and the holding portion 18 is entirely etched. Considering these points, the distance between the acoustic holes 74 and 75 is set to 50 μm. The holding portion 18 is formed only at the corner portion of the element thin film 13, and a vent hole 63 is opened between the holding portions 18. In this way, the microphone 71 having the structure as shown in FIG.

  By manufacturing the microphone 71 in this manner, the through hole 14 can be etched from the front surface side and the back surface side of the Si substrate 12, the area loss due to the inclined surface of the through hole 14 can be reduced, and the microphone 71 can be miniaturized. be able to. Moreover, by combining crystal anisotropic etching and isotropic etching, etching is started from the back side, and the Si substrate 12 is crystal anisotropic etched from the front side and the back side to open the through holes 14. Can do. Therefore, the through-hole 14 can be opened by a simple process, and both cost reduction and high mass productivity can be achieved. In addition, since it is not necessary to open an etching hole in the element thin film 13, there is less risk of lowering the strength of the element thin film 13 or deteriorating vibration characteristics.

  Furthermore, since the element thin film 13 is partially supported by the holding portion 18, the element thin film 13 easily vibrates and the sensitivity of the microphone 71 is improved, and between the element thin film 13 and the Si substrate 12 between the holding portions 18. Since the long vent hole 63 can be formed in the gap, the acoustic resistance of the microphone 71 can be increased and the low frequency characteristics can be improved. Furthermore, since the volume of the through hole 14 can be increased, the acoustic compliance can be increased and the characteristics of the microphone 71 can be improved.

  In each of the above embodiments, the case where the (100) plane Si substrate is used as the substrate has been described, but a (110) plane Si substrate or the like may be used.

FIG. 1A is a plan view showing the structure of a vibration sensor according to Embodiment 1 of the present invention, and FIG. 1B is a sectional view thereof. 2A to 2D are cross-sectional views illustrating the manufacturing process of the vibration sensor according to the first embodiment. FIGS. 3A to 3D are cross-sectional views illustrating the manufacturing process of the vibration sensor according to the first embodiment, and are continued from FIG. FIGS. 4A to 4C are cross-sectional views illustrating the manufacturing process of the vibration sensor according to the first embodiment, and are continued from FIG. FIG. 5A is a plan view showing a vibration sensor according to Embodiment 2 of the present invention, and FIG. 5B is a sectional view thereof. 6A to 6D are cross-sectional views illustrating the manufacturing process of the vibration sensor according to the second embodiment. FIGS. 7A to 7D are cross-sectional views illustrating the manufacturing process of the vibration sensor according to the second embodiment, and are continued from FIG. FIG. 8A is a plan view showing the structure of a vibration sensor according to Embodiment 3 of the present invention, and FIG. 8B is a cross-sectional view taken along line XX of FIG. 9A and 9B are a plan view and a cross-sectional view illustrating a manufacturing process of the vibration sensor according to the third embodiment. 10A to 10D are cross-sectional views illustrating the manufacturing process of the vibration sensor according to the third embodiment and are continued from FIG. FIGS. 11A and 11B are a plan view and a cross-sectional view for explaining the manufacturing process of the vibration sensor according to the third embodiment, and are a continuation of FIG. 12A and 12B are a plan view and a cross-sectional view for explaining the manufacturing process of the vibration sensor according to the third embodiment, and are continued from FIG. FIGS. 13A and 13B are a plan view and a cross-sectional view for explaining the manufacturing process of the vibration sensor according to the third embodiment, and are continued from FIG. FIG. 14A is a plan view showing a structure of a vibration sensor according to Embodiment 4 of the present invention, and FIG. 14B is a sectional view thereof. Fig.15 (a) is a top view which shows the structure of another vibration sensor of Embodiment 4 of this invention, FIG.15 (b) is the sectional drawing. FIG. 16 is a diagram for explaining the function of the vent hole. 17A, 17B, and 17C are cross-sectional views showing a process of continuing etching until the inner peripheral surface of the through hole is depressed. 18A is a plan view of the microphone according to the present invention, and FIG. 18B is a plan view of the microphone in a state where the back plate 72 is removed. FIG. 19 is a cross-sectional view of the microphone. 20 (a) to 20 (d) are cross-sectional views showing the manufacturing process of the microphone according to the present invention. FIGS. 21A to 21D are cross-sectional views illustrating the manufacturing process of the microphone according to the present invention and are continued from FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Vibration sensor 12 Si substrate 13 Element thin film 14 Through-hole 18 Holding part 20, 21 Protective film 22 Etching window 23 Sacrificial layer 24, 25 Protective film 26 Back surface etching window 31 Vibration sensor 32 Sacrificial layer 33 Protective film 41 Vibration sensor 42 Bending part 43 Stopper 44a-44e Sacrificial layer 45, 46 Protective film 49 Protective film 50 Back surface etching window 71 Microphone 72 Back plate 73 Metal electrode 74 Acoustic hole 75 Acoustic hole

Claims (1)

A single semiconductor substrate made of single crystal silicon and formed with through holes penetrating the front and back surfaces;
Made of a material resistant to an etchant for etching the semiconductor substrate to form a through hole, and a holding portion disposed on the surface of the semiconductor substrate;
An element film is supported corners underside, which covers the opening of the substrate surface side of the through hole by the retaining portion,
A back plate disposed on the surface of the semiconductor substrate to cover the element thin film with a gap between the element thin film ,
A vent hole for communicating the surface side and the back side of the element thin film is formed between the holding parts,
The cross-sectional area of the through hole parallel to the substrate surface gradually increases from the surface of the semiconductor substrate toward the back surface, and changes from increasing to decreasing in the middle of the surface and back surface of the semiconductor substrate. Microphone .

Images