JP2009111642A - Fine concave forming method and method for manufacturing condenser microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the reliability of a condenser microphone by forming a concave with no residue in a silicon substrate. <P>SOLUTION: This fine concave forming method includes forming a concave in a silicon substrate by alternately repeating etching and formation of a side wall protective film, removing the side wall protective film to expose the side wall of the concave, and removing the surface layer of the exposed side wall by etching. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for forming a fine recess and a method for manufacturing a condenser microphone, and more particularly to a method for forming a fine recess in a single crystal silicon substrate.

A technique is known in which a deep recess is formed in a silicon substrate by repeating etching with a gas such as SF ₆ and side wall protection by deposition with C ₄ F ₈ or the like. This technique is generally called a Bosch process and is widely used as a process technique for MEMS (Micro Electro Mechanical Systems).

The Institute of Electrical Engineers of Japan MSS-01-34 JP 9-508777 A US Patent No. 4776019 Special table 2004-506394

  However, in the Bosch process, minute etching is formed on the side wall of the recess by repeating isotropic etching. Depending on the process conditions, there is a problem that irregular ridges are formed on the irregularities, or the protruding ends of the irregularities are formed in a brittle form, and these parts fall off as residues. If the residue dropped from the silicon substrate is mixed into the movable part of the MEMS, the function of the MEMS is impaired. In particular, in a condenser microphone, since the gap between the diaphragm and the plate forming the parallel plate capacitor is narrow and wide, the remaining residue significantly reduces the reliability.

  The present invention has been created to solve this problem, and has an object to form a recess having no residue on a silicon substrate and to improve the reliability of a condenser microphone.

(1) A method of forming a fine recess to achieve the above object is to form a recess in a silicon substrate by alternately repeating etching and formation of a sidewall protective film, and remove the sidewall protective film to form a sidewall of the recess. Exposing and removing the exposed surface layer of the sidewall by etching.
After removing the sidewall protective film used to form the recesses in the silicon substrate to expose the sidewalls of the recesses, the surface layer of the exposed sidewalls is removed by etching to remove minute irregularities formed on the sidewalls of the recesses. It is possible to eliminate the shape-like portion and the brittle tip portion of minute unevenness. Therefore, according to the present invention, a recess having no residue can be formed in the silicon substrate.

  (2) In the method for forming fine recesses for achieving the above object, it is desirable to remove the exposed surface layer of the side wall by etching using an alkaline solution.

(3) Tetramethylammonium hydroxide (TMAH) aqueous solution is suitable as an etchant for anisotropically wet etching a single crystal silicon substrate, but has a very high etching selectivity ratio of silicon to silicon oxide. However, a natural oxide film is formed on the surface layer of the side wall of the recess of the silicon substrate from which the side wall protective film has been removed.
Therefore, before removing the exposed surface layer of the sidewall after removing the sidewall protective film, the exposed native oxide film formed on the exposed surface layer of the sidewall is removed, and the sidewall of the sidewall from which the natural oxide film has been removed is removed. It is desirable to remove the surface layer by etching using an aqueous tetramethylammonium hydroxide solution.

(4) A condenser microphone manufacturing method for achieving the above-described object is achieved by alternately repeating etching and forming a sidewall protective film so that a through-hole serving as a back cavity of the diaphragm becomes a silicon oxide film serving as an etching stopper. Formed on the formed silicon substrate, the sidewall protective film is removed to expose the sidewall of the through hole, the natural oxide film formed on the exposed surface layer of the sidewall is removed, and the natural oxide film is removed And removing the surface layer of the side wall by etching using an aqueous tetramethylammonium hydroxide solution.
Condenser microphones require a diaphragm back cavity. The volume of the back cavity is preferably sufficiently large with respect to the area of the diaphragm. Therefore, according to the present invention, a through hole is formed in the silicon substrate, and this through hole is used as at least a part of the back cavity. In the present invention, when the through hole is formed in the silicon substrate by alternately repeating the etching and the formation of the sidewall protective film, the silicon oxide film is used as an etching stopper. When the sidewall protective film is removed, a natural oxide film is formed on the sidewall of the recess. In the present invention, the minute concave and convex ridge-shaped portions formed on the side walls of the concave portions and the brittle tip portions of the minute concave and convex portions are dissolved and disappeared using the TMAH aqueous solution. The etching selectivity of silicon to silicon oxide in the TMAH aqueous solution is very large. Therefore, in the present invention, the natural oxide film formed on the surface layer of the side wall is removed before removing the surface layer on the side wall of the recess with the TMAH aqueous solution. In the present invention, by carrying out such a series of processes, the residue is dropped from the back cavity of the diaphragm, and a problem caused by the dropped residue can be prevented. That is, according to the present invention, the reliability of the condenser microphone can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the corresponding component in each figure, and the overlapping description is abbreviate | omitted.

1. Configuration FIG. 1 shows a sensor chip which is a MEMS structure part of a condenser microphone 1 according to an embodiment of the present invention, FIG. 2 shows a schematic cross section thereof, and FIG. 3 shows a laminated structure of the film. 18 and 19 show a detailed cross section of a part thereof. The condenser microphone 1 includes a sensor chip, a circuit chip (not shown) provided with a power supply circuit and an amplifier circuit, and a package (not shown) that accommodates these.

  The sensor chip of the capacitor microphone 1 is a chip composed of a substrate 100 and a deposited film such as a lower insulating film 110, a lower conductive film 120, an upper insulating film 130, an upper conductive film 160, and a surface insulating film 170 stacked thereon. It is. In FIG. 1, layers above the upper conductive film 160 are not shown. First, the laminated structure of the film of the MEMS structure portion of the condenser microphone 1 will be described.

  The substrate 100 is made of P-type single crystal silicon. The material of the substrate is not limited to this, and it is only necessary to have rigidity, thickness, and toughness as a base substrate for depositing a thin film and a support substrate for supporting a structure made of the thin film. A through hole is formed in the substrate 100, and the opening 100a of the through hole forms an opening of the back cavity C1.

The lower insulating film 110 bonded to the substrate 100, the lower conductive film 120, and the upper insulating film 130 is a deposited film made of silicon oxide (SiO _x ). The lower insulating film 110 includes a plurality of diaphragm support portions 102 arranged at equal intervals on the circumference, a plurality of guard insulation portions 103 arranged at equal intervals on the circumference inside the diaphragm support portion 102, and a guard. An annular portion 101 that insulates the ring 125c and the guard lead 125d from the substrate 100 is formed.

  The lower conductive film 120 bonded to the lower insulating film 110 and the upper insulating film 130 is a deposited film made of polycrystalline silicon doped with impurities such as P as a whole. The lower conductive film 120 forms a guard part 127 including a guard electrode 125a, a guard connector 125b, a guard ring 125c, and a guard lead 125d, and a diaphragm 123.

  The upper insulating film 130 bonded to the lower conductive film 120, the upper conductive film 160, and the lower insulating film 110 is a deposited film made of silicon oxide. The upper insulating film 130 is arranged on the circumference of a plurality of plate support portions 131, and is located outside the plate support portion 131. The upper insulating film 130 supports the etch stopper ring 161 and insulates the plate lead 162d from the guard lead 125d. 132.

  The upper conductive film 160 joined to the upper insulating film 130 is a deposited film made of polycrystalline silicon doped with impurities such as P as a whole. The upper conductive film 160 constitutes a plate 162, a plate lead 162d, and an etch stopper ring 161.

  A surface insulating film 170 bonded to the upper conductive film 160 and the upper insulating film 130 is an insulating deposited film made of a silicon oxide film.

  The MEMS structure portion of the condenser microphone 1 is provided with four terminals 125e, 162e, 123e, and 100b. These terminals 125e, 162e, 123e, and 100b are a conductive conductive film such as AlSi, a pad conductive film 180, a bump film 210 that is a conductive deposited film such as Ni, and a conductive material having excellent corrosion resistance such as Au. A bump protective film 220 which is a conductive deposited film. The side walls of the terminals 125e, 162e, 123e, and 100b are protected by a pad protective film 190 that is an insulating deposited film such as SiN and a surface protective film 200 that is an insulating deposited film such as silicon oxide.

  In the above, the laminated structure of the film | membrane of the MEMS structure part of the capacitor | condenser microphone 1 was demonstrated. Next, the mechanical structure of the MEMS structure part of the condenser microphone 1 will be described.

  The diaphragm 123 is formed of a single-layer thin deposited film having conductivity as a whole, and includes a central portion 123a and a plurality of arm portions 123c extending radially outward from the central portion 123a. The diaphragm 123 is supported by being insulated from the plate 162 with a gap between the plate 162 and the substrate 100 by a plurality of columnar diaphragm support portions 102 joined to a plurality of locations near the outer edge thereof. Are stretched parallel to the substrate 100. The diaphragm support portion 102 is joined to the vicinity of the distal end portion of each arm portion 123 c of the diaphragm 123. Since the diaphragm 123 is notched between the arm part 123c and the arm part 123c, the rigidity is lower than that of the form without the notch. Furthermore, since a plurality of diaphragm holes 123b, which are through holes, are formed in each arm portion 123c, the rigidity of the arm portion 123c itself is low. In the vicinity of the central portion 123a, the arm portion 123c of the diaphragm 123 becomes longer in the circumferential direction of the diaphragm 123 as it approaches the central portion 123a. Thereby, the stress concentration at the boundary between the arm portion 123c and the central portion 123a can be relaxed. Moreover, stress concentration can be prevented from occurring in the bent portion by not forming the bent portion in the outline of the arm portion 123c in the vicinity of the boundary between the arm portion 123c and the central portion 123a.

  The plurality of diaphragm support portions 102 are arranged at equal intervals in the circumferential direction of the opening 100a around the opening 100a of the back cavity C1. Each diaphragm support portion 102 is formed of an insulating deposited film and has a column shape. The diaphragm 123 is supported on the substrate 100 by these diaphragm support portions 102 so that the central portion 123a covers the opening 100a of the back cavity C1. A gap C <b> 2 corresponding to the thickness of the diaphragm support 102 is formed between the substrate 100 and the diaphragm 123. The air gap C2 is necessary to balance the atmospheric pressure of the back cavity C1 with the atmospheric pressure. The gap C2 is low and the radial length of the diaphragm 123 is long so that the acoustic wave that vibrates the diaphragm 123 forms the maximum acoustic resistance in the path to the back cavity opening 100a.

  A plurality of diaphragm bumps 123 f are formed on the surface of the diaphragm 123 that faces the substrate 100. The diaphragm bump 123f is a protrusion for preventing the diaphragm 123 from adhering (sticking) to the substrate 100, and is formed by the undulation of the lower conductive film 120 constituting the diaphragm 123. That is, dimples (dents) are formed on the back side of the diaphragm bump 123f.

The diaphragm 123 is connected to the diaphragm terminal 123e by a diaphragm lead 123d extending from one end of the plurality of arm portions 123c. Diaphragm lead 123d is narrower than arm portion 123c and is formed of lower conductive film 120 that is the same as diaphragm 123. The diaphragm lead 123d extends to the diaphragm terminal 123e through a region where the annular guard ring 125c is divided. Since the diaphragm terminal 123e and the substrate terminal 100b are short-circuited in a circuit chip (not shown) (see FIG. 4), the diaphragm 123 and the substrate 100 are at the same potential.
When the potentials of the diaphragm 123 and the substrate 100 are different, the diaphragm 123 and the substrate 100 form a parasitic capacitance. Even in this case, the diaphragm 123 is supported by the plurality of diaphragm support portions 102. Since an air layer exists between adjacent diaphragm support portions 102, the parasitic capacitance is reduced as compared with a structure in which the diaphragm 123 is supported by a spacer having an annular wall structure.

  The plate 162 is composed of a single layer thin deposited film having conductivity as a whole, and includes a central portion 162b and arm portions 162a extending radially outward from the central portion 162b. The plate 162 is supported by a plurality of columnar plate support portions 131 joined to a plurality of locations near the outer edge thereof. Further, the plate 162 is stretched in parallel with the diaphragm 123 so that the center thereof overlaps the center of the diaphragm 123. The distance from the center of the plate 162 (center of the center portion 162b) to the outer edge of the center portion 162b, that is, the shortest distance from the center of the plate 162 to the outer edge is the outer edge of the center portion 123a from the center of the diaphragm 123 (center of the center portion 123a). Is shorter than the shortest distance from the center of the diaphragm 123 to the outer edge. Therefore, the plate 162 does not face the diaphragm 123 in the region near the outer edge of the diaphragm 123 having a small amplitude. In addition, since a notch is formed between the arm 162a and the arm 162a of the plate 162, the plate 162 and the diaphragm 123 face each other even in the notch region of the plate 162 corresponding to the vicinity of the outer edge of the diaphragm 123. do not do. The arm portion 123 c of the diaphragm 123 extends in the notch region of the plate 162. For this reason, the distance between both ends of the vibration of the diaphragm 123, that is, the distance over which the diaphragm 123 is stretched can be increased without increasing the parasitic capacitance.

  A plurality of plate holes 162 c that are through holes are formed in the plate 162. The plate hole 162c functions as a passage for propagating sound waves to the diaphragm 123, and also functions as a hole through which an etchant for isotropically etching the upper insulating film 130 is passed. The portion remaining after the upper insulating film 130 is etched becomes the plate support portion 131 and the annular portion 132, and the portion removed by the etching becomes the gap C <b> 3 between the diaphragm 123 and the plate 162. That is, the plate hole 162c is a through hole for allowing the etchant to reach the upper insulating film 130 so that the gap C3 and the plate support part 131 can be formed simultaneously. Therefore, the plate hole 162c is arranged according to the height of the gap C3, the shape of the plate support 131, and the etching rate. Specifically, the plate holes 162c are arranged at substantially equal intervals over almost the entire region of the central portion 162b and the arm portion 162a except for the joining region with the plate support portion 131 and the periphery thereof. As the interval between the adjacent plate holes 162c is narrowed, the width of the annular portion 132 of the upper insulating film 130 can be narrowed to reduce the chip area. On the other hand, the rigidity of the plate 162 becomes lower as the interval between the adjacent plate holes 162c is reduced.

  The plate support 131 is joined to a guard electrode 125a located in the same layer as the diaphragm 123 (the guard electrode 125a is made of the same lower conductive film 120 as the diaphragm 123). The plate support 131 is made of an upper insulating film 130 that is an insulating deposited film bonded to the plate 162. The plurality of plate support portions 131 are arranged at equal intervals around the opening 100a of the back cavity C1. Since each plate support part 131 is located in the notch area between the arm part 123c and the arm part 123c of the diaphragm 123, the maximum diameter of the plate 162 can be made smaller than the maximum diameter of the diaphragm 123. This increases the rigidity of the plate 162 and reduces the parasitic capacitance between the plate 162 and the substrate 100.

  The plate 162 is supported on the substrate 100 by a plurality of columnar structures 129 each formed by the guard insulating portion 103, the guard electrode 125 a, and the plate support portion 131. With the structure 129, a gap C <b> 3 is formed between the plate 162 and the diaphragm 123, and a gap C <b> 3 and a gap C <b> 2 are formed between the plate 162 and the substrate 100. Since the guard insulating part 103 and the plate support part 131 have insulation properties, the plate 162 is insulated from the substrate 100.

  When the guard electrode 125a is not provided and the potential of the plate 162 and the potential of the substrate 100 are different, a parasitic capacitance is generated in a region where the plate 162 and the substrate 100 are opposed to each other, and particularly when there is an insulator between them. Increases the parasitic capacitance (see FIG. 4A). In the present embodiment, the structure 129 in which the guard insulating portion 103 that supports the plate 162 on the substrate 100, the guard electrode 125a, and the plate support portion 131 are regarded as one structure is columnar, and a plurality of structures separated from each other. Since the structure is such that the plate 162 is supported on the substrate 100 by a body, even if the guard electrode 125a is not provided, the parasitic capacitance is small compared to the structure in which the plate 162 is supported on the substrate 100 by an insulator having an annular wall structure. Become.

  A plurality of protrusions (plate bumps) 162 f are provided on the surface of the plate 162 that faces the diaphragm 123. The plate bump 162f includes a silicon nitride (SiN) film bonded to the upper conductive film 160 constituting the plate 162, and a polycrystalline silicon film bonded to the silicon nitride film. The plate bump 162f prevents the diaphragm 123 from sticking (sticking) to the plate 162.

A plate lead 162d thinner than the arm 162a extends from the tip of the arm 162a of the plate 162 to the plate terminal 162e. The plate lead 162 d is made of the same upper conductive film 160 as the plate 162. The wiring path of the plate lead 162d overlaps the wiring path of the guard lead 125d. For this reason, the parasitic capacitance between the plate lead 162d and the substrate 100 is reduced.
The mechanical structure of the MEMS structure part of the condenser microphone 1 has been described above.

2. FIG. 4 shows a circuit configured by connecting a circuit chip and a sensor chip. A stable bias voltage is applied to the diaphragm 123 by a charge pump CP provided in the circuit chip. The higher the bias voltage, the higher the sensitivity, but the stiffness of the plate 162 is important because stiction between the diaphragm 123 and the plate 162 tends to occur.

  A sound wave transmitted from a through hole of the package (not shown) is transmitted to the diaphragm 123 through the plate hole 162c and a notch region between the arms of the plate 162. Since the sound wave having the same phase is transmitted from both surfaces to the plate 162, the plate 162 does not substantially vibrate. The sound waves transmitted to the diaphragm 123 cause the diaphragm 123 to vibrate with respect to the plate 162. When the diaphragm 123 vibrates, the capacitance of the parallel plate capacitor having the plate 162 and the diaphragm 123 as the counter electrodes changes. This variation in capacitance is input to the amplifier A of the circuit chip as a voltage signal and amplified. Since the output of the sensor chip is high impedance, an amplifier A is required in the package.

  Since the substrate 100 and the diaphragm 123 are short-circuited, as shown in FIG. 3A, parasitic capacitance is formed by the plate 162 and the substrate 100 that do not vibrate relatively unless the guard electrode 125a of the guard portion 127 is present. As shown in FIG. 3B, the output terminal of the amplifier A is connected to the guard unit 127, and a voltage follower circuit is configured by the amplifier A, so that no parasitic capacitance is formed by the plate 162 and the substrate 100. That is, by providing the guard electrode 125a between the arm portion 162a and the substrate 100 in a region where the arm portion 162a of the plate 162 and the substrate 100 face each other, the parasitic in the region where the arm portion 162a of the plate 162 and the substrate 100 face each other. Capacity can be reduced. Further, since a guard lead 125d extending from the guard ring 125c connecting the guard electrodes to the guard terminal 125e is wired in a region facing the plate lead 162d extending from the plate 162, the plate lead 162d and the substrate 100 also serve as the wiring. Parasitic capacitance is not formed. The annular guard ring 125 c connects the plurality of guard electrodes 125 a with a substantially shortest path around the diaphragm 123. Further, by forming the guard electrode 125a longer than the arm portion 162a of the plate 162 in the circumferential direction of the plate 162, the parasitic capacitance is further reduced.

  Note that it is also possible to configure the one-chip capacitor microphone 1 by providing elements provided in the circuit chip such as the charge pump CP and the amplifier A in the sensor chip.

3. Manufacturing Method Next, a manufacturing method of the condenser microphone 1 will be described with reference to FIGS.

  In the step shown in FIG. 5, first, a lower insulating film 110 made of silicon oxide is formed on the entire surface of the substrate 100. The lower insulating film 110 functions as an etching stopper in the process of forming a through hole in the substrate 100, and forms a maximum acoustic resistance in a path until a sound wave that vibrates the diaphragm 123 reaches the opening 100a of the back cavity. It corresponds to the height of FIG. 2) and also functions as a sacrificial layer for forming the diaphragm bump 123f. Therefore, the thickness of the lower insulating film 110 is set in consideration of these functions, and is set to 1 to 1.5 μm, for example. Next, dimples 110a for forming the diaphragm bumps 123f are formed on the lower insulating film 110 by etching using a photoresist mask. Next, a lower conductive film 120 made of polycrystalline silicon is formed on the surface of the lower insulating film 110 using a CVD method or the like. Then, the diaphragm bump 123f is formed on the dimple 110a. Finally, the lower layer conductive film 120 is etched using a photoresist mask to form the diaphragm 123 and the guard portion 127 made of the lower layer conductive film 120.

  Subsequently, in the process shown in FIG. 6, an upper insulating film 130 made of silicon oxide is formed on the entire surface of the lower insulating film 110 and the lower conductive film 120. Next, a dimple 130a for forming the plate bump 162f is formed on the upper insulating film 130 by etching using a photoresist mask.

  In the subsequent step shown in FIG. 7, a plate bump 162 f made of a polycrystalline silicon film 135 and a silicon nitride film 136 is formed on the surface of the upper insulating film 130. Since the silicon nitride film 136 is formed after the polycrystalline silicon film 135 is patterned by a known method, the entire exposed surface of the polycrystalline silicon film 135 protruding from the dimple 130a is covered with the silicon nitride film 136. The silicon nitride film 136 is an insulating film that prevents the diaphragm 123 and the plate 162 from being short-circuited during sticking.

  8, an upper conductive film 160 made of polycrystalline silicon is formed on the exposed surface of the upper insulating film 130 and the surface of the silicon nitride film 136 using a CVD method or the like. Next, the plate 162, the plate lead 162d, and the etch stopper ring 161 are formed by etching the upper conductive film 160 using a photoresist mask. In this step, the plate hole 162c is not formed.

  Subsequently, in the step shown in FIG. 9, contact holes CH1, CH3, and CH4 are formed in the upper insulating film 130, and then a surface insulating film 170 made of silicon oxide is formed on the entire surface. Further, the contact hole CH2 is formed in the surface insulating film 170 by etching using a photoresist mask, and at the same time, the portion formed at the bottom of the contact holes CH1, CH3, and CH4 of the surface insulating film 170 is removed. Next, a pad conductive film 180 made of AlSi that fills each of the contact holes CH1, CH2, CH3, and CH4 is formed, and is patterned by a well-known method leaving a portion that covers the contact holes CH1, CH2, CH3, and CH4. Further, a pad protection film 190 made of silicon nitride is formed on the surface insulating film 170 and the pad conductive film 180 by the CVD method, and the pad conductive film 190 is patterned by a well-known method so as to remain only around the pad conductive film 180. The

  Subsequently, in the step shown in FIG. 10, through holes 170a corresponding to the plate holes 162c are formed in the surface insulating film 170 by anisotropic etching using a photoresist mask, and the plate holes 162c are formed in the upper conductive film 160. Is done. This process is performed continuously, and the surface insulating film 170 in which the through holes 170a are formed functions as a resist mask for the upper conductive film 160.

  Subsequently, in the step shown in FIG. 11, a surface protective film 200 made of silicon oxide is formed on the surface of the surface insulating film 170 and the pad protective film 190. At this time, the through holes 170 a and the plate holes 162 c of the surface insulating film 170 are filled with the surface protective film 200.

  Subsequently, in the step shown in FIG. 12, a bump film 210 made of Ni is formed on the surface of the pad conductive film 180 formed in each of the contact holes CH1, CH2, CH3, and CH4, and the surface of the bump film 210 is made of Au. A bump protective film 220 is formed. Further, at this stage, the back surface of the substrate 100 is ground to make the thickness of the substrate 100 a final dimension of 525 μm.

  Subsequently, in a step shown in FIG. 13, through holes H5 in which the etch stopper ring 161 is exposed are formed in the surface protective film 200 and the surface insulating film 170 by etching using a photoresist mask.

  The film formation process on the surface side of the substrate 100 is completed through the above steps. In the state where all the film formation processes on the surface side of the substrate 100 have been completed, in the step shown in FIG. Formed on the back surface.

Subsequently, in a step shown in FIG. 15, a through hole having a penetration length of 525 μm for forming the back cavity C1 is formed in the substrate 100 by deep substrate etching (Deep-RIE). That is, in this step, a fluorine-containing gas such as SF ₆ gas for etching the substrate 100 made of single crystal silicon, and a sidewall protective film Rs for protecting the sidewall of the recess formed by etching (see FIG. 20A). Etching and deposition are repeated in small increments by alternately supplying C _x F _y gas for forming a film, and the surface of the substrate 100 (the plane having a plane orientation of 100, which is an interface with the photoresist mask R1). A substantially vertical sidewall 100c is formed. More specifically, for example, SF ₆ gas and C _x F _y gas are preferably 10 seconds or less, preferably under conditions of a flow rate of 200 to 500 sccm, a pressure of 2 to 10 Pa, a stage temperature of 10 ° C., and a surface temperature of the substrate 100 of 70 to 80 ° C. Is supplied into the chamber while switching at intervals of 2 to 3 seconds, and for example, a through hole having a diameter of 600 μm is formed. In this step, the lower insulating film 110 made of silicon oxide serves as an etching stopper.
In the step shown in FIG. 15, as shown in FIG. 20A, approximately regular minute irregularities are formed on the side wall 100 c of the through hole. In addition, on the side wall 100c of the through hole, a bowl-shaped portion 100d and a rugged bulge end portion 100e are irregularly generated, or a residue 100f in which such a portion is dropped from the substrate 100 is generated. In particular, in the vicinity of the interface with the photoresist mask R1 and the vicinity of the interface with the lower insulating film 110, such a rough side wall that generates the residue 100f is likely to occur. When the substrate deep etching is performed under the above-described conditions, the lower insulating film 110 serving as an etching stopper is also etched by about 0.5 μm as shown in FIG. 20A.
When the side wall 100c is completed in a state where the through hole side wall 100c is rough as shown in FIG. 20A, as shown in FIG. Drops off to give a new residue.

  Therefore, subsequently, in the step shown in FIG. 16, the photoresist mask R1 and the sidewall protective film Rs are removed, and the sidewall 100c of the through hole roughly formed in the substrate 100 by the substrate deep etching is smoothed.

  That is, first, ashing is performed to remove the photoresist mask R1 and the sidewall protective film Rs shown in FIG. 20A with oxygen plasma, organic stripping solution, or the like. Next, in order to protect the deposited film other than the lower insulating film 110 already formed on the substrate 100, the resist film Rb is formed on the entire front surface of the substrate 100 (the entire surface on which the surface protective film 200 is formed). (See FIG. 16). Next, the natural oxide film formed on the surface layer of the sidewall 100c of the recess of the substrate 100 exposed by removing the sidewall protective film Rs is removed using dilute hydrofluoric acid (BHF), hydrofluoric acid, or the like as an etchant. At this time, the natural oxide film can be completely removed, and the etching end point is controlled in a range in which the lower insulating film 110 functions as an etching stopper. That is, the etching end point is controlled so that the lower conductive film 120 is not exposed. Specifically, for example, when the lower insulating film 110 is 1 to 1.5 μm, the natural oxide film is removed by immersing in 1100 BHF at 23 ° C. for 60 seconds and removing the surface layer of the substrate 100 by about 5 to 20 nm. When the etching end point is controlled in the range of “etching depth by dilute hydrofluoric acid or hydrofluoric acid <thickness of the lower insulating film− (etching depth of the lower insulating film by substrate deep etching + diaphragm bump height)”, Even if the diaphragm bump 123 f made of the lower conductive film 120 is located at a position very close to the through hole of the substrate 100, the lower conductive film 120 is not exposed. Next, the etchant is washed with pure water.

  Next, the entire surface layer of the exposed surface of the substrate 100 is removed by crystal anisotropic wet etching using an alkaline solution. The concentration and temperature of the TMAH aqueous solution may be optimized as appropriate. For example, the substrate 100 is immersed in NMD-3, which is a TMAH aqueous solution having a concentration of 2.38%, for 15 minutes to 30 minutes, and the surface layer of the entire exposed surface of the substrate 100 is formed. Remove. The temperature of NMD-3 is 23 ° C., for example. The depth at which the surface layer of the substrate 100 is removed may be set according to the thickness of the bowl-shaped portion 100. For example, the substrate 100 is removed to a depth of 2 μm. Then, the residue 100f dropped off from the substrate 100 disappears, and the ridge-shaped portion 100d and the uneven bulge end portion 100e disappear. As a result, as shown in FIG. 20B, a brittle portion disappears from the side wall 100c of the through hole, and the residue of the substrate 100 disappears. By performing such a series of smoothing steps, problems due to the residue of the substrate 100 generated during manufacturing and the residue generated after manufacturing are prevented, and the reliability of the condenser microphone 1 is improved.

  Subsequently, in the step shown in FIG. 17, the surface layer protective film 200 and the surface layer insulating film 170 on the plate 162 and the plate lead 162d are removed by isotropic etching using the photoresist mask R2 and BHF, and the upper layer insulating film is further removed. A part of the film 130 is removed to form the annular part 132, the plate support part 131, and the gap C3, and a part of the lower insulating film 110 is removed to remove the guard insulating part 103, the diaphragm support part 102, the annular part 101, and the gap. C2 is formed. At this time, the etchant BHF enters from each of the through hole H6 of the photoresist mask R2 and the opening 100a of the substrate 100. The contour of the upper insulating film 130 is defined by the plate 162 and the plate lead 162d. That is, the annular portion 132 and the plate support portion 131 are formed by self-alignment with the plate 162 and the plate lead 162d. As shown in FIG. 18, an undercut is formed on the end surfaces of the annular portion 132 and the plate support portion 131 by isotropic etching. The contour of the lower insulating film 110 is defined by the opening 100a of the substrate 100, the diaphragm 123, the diaphragm lead 123d, the guard electrode 125a, the guard connector 125b, and the guard ring 125c. That is, the guard insulating portion 103 and the diaphragm support portion 102 are formed by self-alignment with the diaphragm 123. Undercuts are formed on the end surfaces of the guard insulating portion 103 and the plate support portion 131 by isotropic etching (see FIGS. 18 and 19). In this step, since the guard insulating portion 103 and the plate support portion 131 are formed, the portion excluding the guard electrode 125a of the structure 129 that supports the plate 162 on the substrate 100 is formed in this step.

  Finally, the photoresist mask R2 is removed and the substrate 100 is diced to complete the sensor chip of the condenser microphone 1 shown in FIG. When the sensor chip and the circuit chip are bonded to a package substrate (not shown), the terminals are connected by wire bonding, and a package cover (not shown) is placed on the package substrate, the capacitor microphone 1 is completed. By bonding the sensor chip to the package substrate, the back cavity C1 is hermetically closed on the back side of the substrate 100.

4). Other Embodiments The technical scope of the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the scope of the present invention. For example, the materials and dimensions shown in the above embodiment are merely examples, and descriptions of addition and deletion of processes and replacement of the process order that are obvious to those skilled in the art are omitted. In the manufacturing process described above, the film composition, film forming method, film outline forming method, process sequence, etc. are combinations of film materials having physical properties that can constitute a condenser microphone, film thickness, and required outline. It is appropriately selected according to the shape accuracy and the like and is not particularly limited.

Specifically, in the process shown in FIG. 16, crystal anisotropic wet etching using another alkaline solution such as a KOH aqueous solution or a choline chloride [(CH ₃ ) ₃ NC ₂ H ₄ Cl] aqueous solution in place of the TMAH aqueous solution. May remove the surface layer of the side wall 100c of the through hole. Further, the surface layer of the sidewall 100c of the through hole may be removed by isotropic dry etching or wet etching instead of crystal anisotropic wet etching using an alkaline solution.

  In addition, the present invention can be applied to manufacture of MEMS other than a condenser microphone such as a magnetic sensor, an acceleration sensor, an attitude sensor, and a pressure sensor, and can also be applied to manufacture of semiconductor devices other than MEMS.

The top view concerning embodiment of this invention. The typical sectional view concerning the embodiment of the present invention. The disassembled perspective view concerning embodiment of this invention. The circuit diagram concerning the embodiment of the present invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention.

Explanation of symbols

1: condenser microphone, 100: substrate (silicon substrate), 100a: opening, 100b: substrate terminal, 100c: side wall, 101: annular portion, 102: diaphragm support portion, 103: guard insulating portion, 110: lower insulating film, 110a : Dimple, 120: Lower conductive film, 123: Diaphragm, 123a: Center part, 123b: Diaphragm hole, 123c: Arm part, 123d: Diaphragm lead, 123e: Diaphragm terminal, 123f: Diaphragm bump, 125a: Guard electrode, 125b: Guard connector, 125c: guard ring, 125d: guard lead, 125e: guard terminal, 127: guard part, 129: structure, 130: upper insulating film, 130a: dimple, 131: plate support part, 132: annular part, 160 : Upper layer conductive film, 161 Etch stopper ring, 162: plate, 162a: arm portion, 162b: central portion, 162c: plate hole, 162d: plate lead, 162e: plate terminal, 162f: plate bump, 170: surface insulating film, 180: pad conductive film, 190: pad protective film, 200: surface protective film, 210: bump film, 220: bump protective film, A: amplifier, C1: back cavity, C2: air gap, C3: air gap, CP: charge pump

Claims (4)

Etching and sidewall protection film formation are repeated alternately to form a recess in the silicon substrate,
Removing the sidewall protective film to expose the sidewall of the recess,
Removing the exposed surface layer of the sidewall by etching;
A method for forming a fine recess. Removing the exposed surface layer of the sidewall by etching using an alkaline solution;
The fine recessed part formation method of Claim 1 including this. Before removing the exposed surface layer of the side wall after removing the side wall protective film, the natural oxide film formed on the exposed surface layer of the side wall is removed,
Removing the surface layer of the side wall from which the natural oxide film has been removed by etching using a tetramethylammonium hydroxide aqueous solution;
The fine recessed part formation method of Claim 1 or 2. By alternately repeating the etching and the formation of the sidewall protective film, a through-hole serving as a back cavity of the diaphragm is formed on the silicon substrate on which the silicon oxide film serving as an etching stopper is formed,
Removing the sidewall protective film to expose the sidewall of the through hole;
Removing the natural oxide film formed on the exposed surface layer of the sidewall;
Removing the surface layer of the side wall from which the natural oxide film has been removed by etching using a tetramethylammonium hydroxide aqueous solution;
A method of manufacturing a condenser microphone.

Images