JP6863545B2 - MEMS device and its manufacturing method - Google Patents

Description

The present invention relates to a MEMS device, particularly a capacitive MEMS device used as a microphone, various sensors, a switch, etc., and a method for manufacturing the same.

Conventionally, MEMS (Micro Electro Mechanical Systems) devices using a semiconductor process have spacers by forming a fixed electrode, a sacrificial layer (insulating film) and a movable electrode on a semiconductor substrate, and then removing a part of the sacrificial layer. An air gap (hollow) structure is formed between the fixed electrode and the movable electrode fixed via the above.

For example, in a condenser microphone which is a capacitive MEMS element, a fixed electrode having a plurality of through holes for passing sound pressure and a movable electrode (diaphragm film) that vibrates in response to sound pressure are arranged so as to face each other. The configuration is such that the displacement of the movable electrode that vibrates in response to sound pressure is detected as a capacitance change between the electrodes.

FIG. 4 is an explanatory diagram of a general method for manufacturing a condenser microphone. First, a thermal oxide film 2 having a thickness of about 1 μm is formed on a silicon substrate 1 having a crystal orientation (100) plane with a thickness of 420 μm, and the thickness is 0 on the thermal oxide film 2 by a CVD (Chemical Vapor Deposition) method. . A conductive polysilicon film of about 2 to 2.0 μm is laminated. Next, the conductive polysilicon film is patterned by a normal photolithography method to form the movable electrode 6 (FIG. 4a).

Next, a sacrificial layer 7 made of a USG (Undoped Silicate Glass) film serving as a first spacer having a thickness of about 2.0 to 5.0 μm is laminated on the movable electrode 6 and further thickened on the sacrificial layer 7. A conductive polysilicon film having a size of 0.1 to 1.0 μm is laminated and formed. The conductive polysilicon film is patterned by a normal photolithography method to form the fixed electrode 8. A nitride film is further laminated on the fixed electrode 8 by a reduced pressure CVD method to form a back plate 9 integrated with the fixed electrode 8. A through hole 10 is formed in the fixed electrode 8 and the back plate 9 to expose the sacrificial layer 7 (FIG. 4b).

After that, the back chamber 11 is formed by etching the silicon substrate 1 from the back surface side until the thermal oxide film 2 is exposed. Finally, a part of the sacrificial layer 7 is etched from the through hole 10 to form the first spacer 12, and at the same time, a part of the thermal oxide film remaining on the back chamber 11 side is etched to form the second spacer 13. , A MEMS element in which the fixed electrode 8 and the movable electrode 6 face each other is formed (FIG. 4c). A method for manufacturing such a general condenser microphone is described in, for example, Patent Document 1.

Japanese Unexamined Patent Publication No. 2007-274096

By the way, when the back chamber 11 is formed by etching the silicon substrate 1 in this way, it is necessary to etch the silicon substrate 1 very deeply, so that the bottom surface of the silicon substrate 1 (back chamber side surface end portion 15) is smooth. It does not become a perfect circle, and protrusions remain. FIG. 5 schematically shows the end portion of the second spacer 13 formed by etching the side surface end portion of the back chamber 11 and a part of the thermal oxide film from the movable electrode 6 side. As shown in FIG. 5, when the protrusion 16 is formed on the side end portion 15 of the back chamber, the thermal oxide film is isotropically etched, so that the protrusion 17 is also formed on the side end portion of the second spacer 13. Will be formed. When pressure is applied to the movable electrode 6 supported by the second spacer 13 in which the protrusion 17 is present, stress is concentrated on the connection point 18 between the tip of the protrusion 17 of the second spacer 13 and the movable electrode 6. However, there is a problem that the movable electrode 6 is easily broken.

An object of the present invention is to provide a MEMS device and a method for manufacturing the same, which can solve the above problems and prevent the MEMS device from being destroyed.

In order to achieve the above object, in the invention according to claim 1 of the present application, air is provided by arranging a silicon substrate provided with a back chamber and a fixed electrode and a movable electrode on the silicon substrate with a first spacer interposed therebetween. In the MEMS element in which the gap is formed, the dimension between the second spacer between the silicon substrate and the movable electrode and the movable electrode facing the silicon substrate is increased on the side surface end side of the back chamber. A step portion is provided, and the step portion is arranged in an annular shape along the side surface of the silicon substrate between the thermal oxide film constituting the second spacer and the side surface of the silicon substrate constituting the back chamber. It is characterized by being.

The invention according to claim 2 of the present application is a method for manufacturing a MEMS element in which a fixed electrode and a movable electrode are arranged with a first spacer sandwiched on a silicon substrate provided with a back chamber. A step of thermally oxidizing the surface of the silicon substrate so as to fill the inside of the annular recess arranged inside, a step of forming the movable electrode on the thermal oxide film of the surface of the silicon substrate, and a step of forming the movable electrode on the movable electrode. A step of forming an insulating film, a step of forming the fixed electrode on the insulating film, a step of forming a through hole in the fixed electrode, and a part of the silicon substrate are etched and removed, and the side surface is described as described above. In the step of forming the back chamber so as to be located in the annular recess, a part of the insulating film is removed by etching from the through hole to form the first spacer, and the fixed electrode and the movable electrode are formed. At the same time as forming an air gap between the two, the step of removing the thermal oxide film embedded in the recess, leaving a part of the thermal oxide film on the surface of the silicon substrate, and forming a second spacer is included. It is characterized by that.

The MEMS element manufactured by the method for manufacturing a MEMS element of the present invention has a smooth circular shape in which a protrusion is not formed on the side end of the second spacer even if a protrusion is formed on the side end of the back chamber. The shape can prevent the movable electrode from being destroyed. Further, the protrusion can be separated from the movable electrode and can be prevented from coming into contact with the protrusion and being damaged when the movable electrode vibrates.

Since the method for manufacturing a MEMS device of the present invention is composed of only commonly used steps in a normal manufacturing process for a semiconductor device, the MEMS device can be formed very stably and inexpensively. There is an advantage that it can be done. In particular, due to thermal oxidation of the silicon substrate, the side end of the back chamber is formed because etching is started from the thermal oxide film filled in the concave portion whose side surface and bottom surface are smooth. Even if the protrusion is left on the surface, there is an advantage that the protrusion is not formed on the side end of the second spacer.

It is explanatory drawing of the manufacturing process of the MEMS element of this invention. It is explanatory drawing of the manufacturing process of the MEMS element of this invention. It is a figure explaining the effect of the manufacturing method of the MEMS element of this invention. It is explanatory drawing of the manufacturing process of the conventional MEMS element. It is a figure explaining the effect of the manufacturing method of the conventional MEMS element.

In the MEMS element according to the present invention, the surface of the silicon substrate is thermally oxidized to form a thermal oxide film so that the space between the side surface end of the back chamber and the region where the second spacer is formed is partially thickened. Since this thermal oxide film is formed according to a normal manufacturing process of a semiconductor device, the shape of the thick portion can be formed into a smooth annular shape, for example, a circular shape. Moreover, by forming a thick thermal oxide film inside the thermal oxide film remaining as the second spacer, it is possible to form a structure that is not affected by the protrusions remaining on the side end portions of the back chamber. Hereinafter, examples of the present invention will be described according to the method for manufacturing a MEMS device of the present invention.

Examples of the present invention will be described according to the manufacturing process. _{First, a thermal oxide film 2 (SiO 2} ) having a thickness of about 1 μm is formed on a silicon substrate 1 having a thickness of 420 μm on the crystal orientation (100) plane, and the thermal oxide film 2 is patterned by a normal photolithography method. A plurality of annular grooves 3 having a width of about 0.5 μm and a depth of about 1 μm are formed on the silicon substrate 1 along the peripheral edge of the silicon substrate 1. At this time, the outermost circumference of the annular groove 3a of the annular groove 3 is formed so as to be outside the planned position for forming the back chamber and inside the planned position for forming the second spacer (FIG. 1a).

After that, the surface of the silicon substrate 1 is thermally oxidized to thermally oxidize the silicon substrate 4 between the annular grooves 3 to form the annular recess 5, and at the same time, the inside of the annular recess 5 is filled with the thermal oxide film 2a (FIG. 1b). If a plurality of annular grooves 3 are formed in order to fill the inside of the annular recess 5 with the thermal oxide film 2a, the surface of the thermal oxide film 2a becomes flat after thermal oxidation, which is a simple method.

Hereinafter, a conductive polysilicon film having a thickness of about 0.2 to 2.0 μm is laminated and formed on the thermal oxide film 2 by a CVD (Chemical Vapor Deposition) method according to a normal manufacturing process. Next, the conductive polysilicon film is patterned by a normal photolithography method to form the movable electrode 6 (FIG. 1c).

Next, a sacrificial layer 7 made of a USG (Undoped Silicate Glass) film serving as a first spacer having a thickness of about 2.0 to 5.0 μm is laminated on the movable electrode 6 and further thickened on the sacrificial layer 7. A conductive polysilicon film having a size of 0.1 to 1.0 μm is laminated and formed. The conductive polysilicon film is patterned by a normal photolithography method to form the fixed electrode 8. A nitride film is further laminated on the fixed electrode 8 by a reduced pressure CVD method to form a back plate 9 integrated with the fixed electrode 8. A through hole 10 is formed in the fixed electrode 8 and the back plate 9 to expose the sacrificial layer 7 (FIG. 2a).

After that, the back chamber 11 is formed by etching the silicon substrate 1 from the back surface side until the thermal oxide film 2 is exposed. At this time, as shown in FIG. 2B, the side wall end portion of the back chamber 11 is arranged so as to be the bottom portion of the thermal oxide film 2a embedded in the annular recess 5 formed earlier.

Finally, a part of the sacrificial layer 7 is etched from the through hole 10 to form the first spacer 12, and at the same time, a part of the thermal oxide film 2 remaining on the back chamber 11 side is etched to form the second spacer 13. Then, a MEMS element in which the fixed electrode 8 and the movable electrode 6 face each other is formed (FIG. 2c).

In the MEMS element formed in this way, as shown in FIG. 3, when the back chamber 11 is formed, even if the protrusion 16 is formed on the side end portion 14 of the back chamber, the side end of the second spacer 13 is formed. No protrusions are formed on the portion, resulting in a smooth circular shape. This is because when the thermal oxide film is etched, the side surface portion 2b and the bottom surface of the thermal oxide film 2a have a smooth circular shape, so that isotropic etching is performed so as to trace the smooth circular surface. This is because it progresses and no protrusion is formed. Further, since the protrusion 16 is formed on the side wall end portion 14 of the back chamber, the etching of the thermal oxide film 2 proceeds so as to trace the protrusion, but this etching reaches the side surface portion 2c of the thermal oxide film 2a. Then, all the thermal oxide films 2a are etched, and the etching shape of the second spacer 13 is not affected. In this way, by adopting a structure without protrusions, even if pressure is applied to the movable electrode 6, stress does not concentrate at a specific connection point between the second spacer 13 and the movable electrode 6, and the movable electrode 6 has a structure. It will be possible to prevent destruction.

As described above, the present invention is not limited to this, and various modifications can be made. For example, the method of filling the annular recess 5 with a thermal oxide film is not limited to the method of forming a plurality of annular grooves 3 as shown in FIG. 1A, and thermal oxidation is performed in the wide recess. The membrane may be filled to form the annular recess 5. Further, the shape of the movable electrode, the recess in which the thermal oxide film is embedded, and the like is not limited to a circle.

1: Silicon substrate 2: Thermal oxide film, 2a, 2b, 2c: Thermal oxide film embedded in the annular recess, 3, 3a: Circular groove 4: Silicon substrate between the annular grooves 3, 5: Annular recess, 6 : Movable electrode, 7: Sacrificial layer, 8: Fixed electrode, 9: Back plate, 10: Through hole, 11: Back chamber, 12: First spacer, 13: Second spacer, 14, 15: Back chamber side surface Ends, 16, 17: protrusions, 18: connection points

Claims (2)

In a silicon substrate provided with a back chamber and a MEMS element in which an air gap is formed by arranging a fixed electrode and a movable electrode on the silicon substrate with a first spacer interposed therebetween.
A second spacer between the silicon substrate and the movable electrode ,
A step portion for increasing the dimension between the silicon substrate and the movable electrode facing the silicon substrate on the side surface end side of the back chamber is provided.
The step portion is characterized in that it is annularly arranged along the side surface of the silicon substrate between the thermal oxide film constituting the second spacer and the side surface of the silicon substrate constituting the back chamber. MEMS element. In a method for manufacturing a MEMS element in which a fixed electrode and a movable electrode are arranged on a silicon substrate provided with a back chamber with a first spacer interposed therebetween.
A step of thermally oxidizing the surface of the silicon substrate so as to fill the inside of the annular recess arranged inside the second spacer formation planned region, and
The step of forming the movable electrode on the thermal oxide film on the surface of the silicon substrate, and
The step of forming an insulating film on the movable electrode and
The step of forming the fixed electrode on the insulating film and
The step of forming a through hole in the fixed electrode and
A step of etching and removing a part of the silicon substrate to form the back chamber so that the side surface is located in the annular recess.
A part of the insulating film is removed by etching from the through hole to form the first spacer, an air gap is formed between the fixed electrode and the movable electrode, and at the same time, heat embedded in the recess is formed. A method for manufacturing a MEMS element, which comprises a step of removing an oxide film, leaving a part of a thermal oxide film on the surface of the silicon substrate, and forming a second spacer.

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