JP6784005B2 - MEMS device and its manufacturing method - Google Patents

Description

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

Conventionally, in a MEMS (Micro Electro Mechanical Systems) element using a semiconductor process, a movable electrode, a sacrificial layer, and a fixed electrode are formed on a semiconductor substrate, and then a part of the sacrificial layer is removed to fix the element via a spacer. An air gap (hollow) structure is formed between the movable electrode and the fixed electrode.

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 that vibrates in response to sound pressure are arranged to face each other and receive sound pressure. The configuration is such that the displacement of the vibrating movable electrode is detected as a change in capacitance between the electrodes.

By the way, in order to increase the sensitivity of the condenser microphone, it is necessary to increase the displacement of the movable electrode due to sound pressure. Therefore, as the movable electrode, a film in which tensile stress remains is generally used. On the other hand, if this residual stress is too large, it causes damage to the movable electrode.

Therefore, a method of controlling the residual stress of the film itself and a method of mitigating the influence of the residual stress by devising a structure have been proposed. Specifically, in the former case, the fixed electrode is deposited by the LPCVD (Low Pressure Chemical Vapor Deposition) method, and the annealing conditions after the deposition are controlled to adjust the residual stress. In the latter case, a slit is formed. A method of adjusting the residual stress has been proposed by the method of adjusting the residual stress (Patent Document 1).

FIG. 14 is an explanatory diagram of a conventional MEMS device in which a slit is formed. As shown in FIG. 14, the movable electrode 8 is formed on the silicon substrate 1 via the thermal oxide film 2. A fixed electrode 10 and a nitride film 12 are formed on the movable electrode 8 via a spacer 15, and a through hole 13 is formed in a back plate composed of the fixed electrode 10 and the nitride film 12. On the other hand, a slit 20 is formed in the movable electrode 8 to adjust the residual stress. The air gap 21 formed between the movable electrode 8 and the fixed electrode 10 has a structure of communicating with the back chamber 14 formed on the silicon substrate 1 via the slit 20.

JP-A-2007-210083

By the way, when forming a slit in a movable electrode, if the thickness of the movable electrode becomes thick, it becomes difficult to finely process the slit, so that the slit width becomes wide. As a result, there is a problem that the low frequency sensitivity is lowered. On the other hand, if the movable electrode is made thin, the slit width can be narrowed, and the decrease in low frequency sensitivity can be suppressed. However, as a result, there is a problem that the strength of the movable electrode itself is lowered. In order to solve such a problem, it is an object of the present invention to provide a MEMS element capable of suppressing a decrease in low frequency sensitivity of the MEMS element and maintaining the strength of a movable electrode, and a method for manufacturing the same.

In order to achieve the above object, in the invention according to claim 1 of the present application, an air gap is formed by arranging a substrate provided with a back chamber and a fixed electrode and a movable electrode on the substrate with a spacer interposed therebetween. In the MEMS element, the movable electrode is composed of at least a first membrane layer and a second membrane layer thinner than the first membrane layer, and a plurality of moving electrodes penetrating the first membrane layer and the second membrane layer. The slits are formed, and the slits are arranged so as to overlap the first slit formed on the first membrane layer and the second slit formed on the second membrane layer. It is characterized in that the width of the second slit is narrower than the width of the first slit.

The invention according to claim 2 of the present application is a method of manufacturing a MEMS element in which a fixed electrode and a movable electrode are arranged with a spacer interposed therebetween on a substrate provided with a back chamber, in which a first insulating film is formed on the substrate surface. The step and a second thinner than the first membrane layer having the first slit or the first membrane layer having the second slit having a width narrower than the width of the first slit on the first insulating film. In the step of forming the membrane layer of the above, the second membrane layer is formed on the first membrane layer, or the first membrane layer is formed on the second membrane layer, and the first membrane layer is formed. A step of forming a movable electrode including the second membrane layer, a step of forming a second insulating film on the movable electrode, and a step of forming the fixed electrode on the second insulating film. A step of forming a through hole in the fixed electrode, a step of etching and removing a part of the substrate to form the back chamber, and a step of etching and removing a part of the second insulating film from the through hole. , The spacer is formed to form an air gap between the fixed electrode and the movable electrode, and at the same time, a part of the first insulating film is removed to form the first slit and the second slit. It is characterized by including a step of exposing the movable electrode with which the movable electrode communicates.

In the invention according to claim 3 of the present application, in the method for manufacturing a MEMS element according to claim 2, the step of forming a movable electrode including the second membrane layer on the first membrane layer is the first slit. The step of forming the movable electrode includes the step of forming the second membrane layer after filling the inside with the third insulating film, and the step of forming the movable electrode is one of the first insulating films at the same time as forming the air gap. It is characterized by including a step of removing the portion and the third insulating film to form the movable electrode in which the first slit and the second slit communicate with each other.

The MEMS device manufactured by the method for manufacturing a MEMS device of the present invention has a multilayer structure in which a movable electrode is composed of membrane layers having different thicknesses, and a slit formed in the movable electrode is a wide slit formed in a thick membrane layer. It is composed of narrow slits formed in a thin membrane layer. Therefore, it is possible to suppress a decrease in low frequency sensitivity by using a narrow slit. At the same time, the thick membrane layer can reinforce the thin membrane layer and give the movable electrode strength.

Further, according to the method for manufacturing a MEMS element of the present invention, when a movable electrode including a second membrane layer is formed on the first membrane layer, the first slit of the lower first membrane layer is formed into a third. By embedding it with an insulating film, it becomes easy to narrow the width of the second slit of the second membrane layer formed on the upper layer, and the effect is great.

It is explanatory drawing of the manufacturing process of the MEMS element which concerns on 1st Example of this invention. It is explanatory drawing of the manufacturing process of the MEMS element which concerns on 1st Example of this invention. It is explanatory drawing of the manufacturing process of the MEMS element which concerns on 1st Example of this invention. It is explanatory drawing of the manufacturing process of the MEMS element which concerns on 1st Example of this invention. It is explanatory drawing of the manufacturing process of the MEMS element which concerns on 1st Example of this invention. It is explanatory drawing of the MEMS element which concerns on 1st Example of this invention. It is explanatory drawing of the manufacturing process of the MEMS element which concerns on 2nd Example of this invention. It is explanatory drawing of the MEMS element which concerns on 2nd Example of this invention. It is explanatory drawing of the manufacturing process of the MEMS element which concerns on 3rd Example of this invention. It is explanatory drawing of the manufacturing process of the MEMS element which concerns on 3rd Example of this invention. It is explanatory drawing of the MEMS element which concerns on 3rd Example of this invention. It is explanatory drawing of the manufacturing process of the MEMS element which concerns on 4th Example of this invention. It is explanatory drawing of the MEMS element which concerns on 4th Example of this invention. It is explanatory drawing of the conventional MEMS element.

In the MEMS element according to the present invention, the movable electrode has a multi-layer structure composed of a plurality of membrane layers having different thicknesses, and the slits formed in the movable electrodes are formed in a wide slit formed in the thick membrane layer and a thin membrane layer. By arranging the narrow slits so as to overlap each other, it is possible to suppress a decrease in low frequency sensitivity and maintain the strength of the movable electrode. Hereinafter, an embodiment of the present invention will be described according to the method for manufacturing a MEMS element of the present invention, taking a condenser microphone as an example of the MEMS element.

A first embodiment of the present invention will be described. First, a thermal oxide film 2 (corresponding to the first insulating film) 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 CVD (corresponding to the first insulating film) is formed on the thermal oxide film 2. A conductive polysilicon film having a thickness of about 1 μm is laminated and formed by the Chemical Vapor Deposition) method. Next, patterning is performed by a normal photolithography method to form a first membrane layer 4 having a first slit 3 having a width of about 1 to 2 μm (FIG. 1).

After that, an oxide film is laminated and formed on the first membrane layer 4 by a CVD method, and the inside of the first slit 3 is embedded with an oxide film 5 (corresponding to a third insulating film) to flatten it. Next, the oxide film on the first membrane layer 4 is removed, the oxide film 5 is left in the first slit 3, and the first membrane layer 4 is exposed. Then, a conductive polysilicon film having a thickness of about 0.08 μm is laminated on the first membrane layer 4 and the oxide film 5. Next, the second membrane layer 7 in which the second slit 6 having a width of about 0.1 to 0.2 μm is arranged on the oxide film 5 embedded in the first slit 3 after patterning by a normal photolithography method is formed. Form (Fig. 2).

Hereinafter, according to a normal manufacturing process, a sacrifice made of a USG (Undoped Silicate Glass) film having a thickness of about 2.0 to 4.0 μm is formed on a movable electrode 8 composed of a first membrane layer 4 and a second membrane layer 7. A layer 9 (corresponding to a second insulating film) is laminated and formed, and a conductive polysilicon film having a thickness of about 0.1 to 1.0 μm is further laminated on the sacrificial layer 9. Next, the fixed electrodes 10 are laminated and formed by patterning by a normal photolithography method (FIG. 3).

A part of the sacrificial layer 9 is removed by etching to expose a part of the movable electrode 8 formed earlier. A wiring film 11 made of a conductor film such as aluminum connected to the exposed movable electrode 8 and the fixed electrode 10 is formed (FIG. 4).

After the nitride film 12 is deposited on the entire surface, a through hole 13 for transmitting sound pressure to the movable electrode 8 is formed by a normal photolithography method, and the sacrificial layer 9 is exposed in the through hole 13. After that, the silicon substrate 1 is removed from the back surface side of the silicon substrate 1 until the thermal oxide film 2 is exposed to form the back chamber 14 (FIG. 5).

After that, by removing a part of the sacrificial layer 9 through the through hole 13 formed in the nitride film 12 and the fixed electrode 10, an air gap structure in which the fixed electrode 10 and the movable electrode 8 are fixed by the spacer 15 is formed. .. By this etching, a part of the thermal oxide film 2 and the oxide film 5 in the first slit are also removed (FIG. 6a). As a result, the first slit 3 and the second slit 6 are opened (FIG. 6b).

As shown in FIG. 6B, the slit of the MEMS element of the present embodiment formed in this way is composed of a wide first slit 3 and a narrow second slit 6. The narrow second slit 6 makes it possible to suppress a decrease in low frequency sensitivity. Further, since the movable electrode is composed of the thick first membrane layer 4 and the thin second membrane layer 7, the thin second membrane layer 7 can be reinforced by the thick first membrane layer 4, so that the movable electrode is movable. It is possible to give strength to the electrode 8.

Next, a second embodiment of the present invention will be described. First, as in the first embodiment, 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 a thermal oxide film 2 having a thickness of about 1 μm is formed on the thermal oxide film 2 by a CVD method. A conductive polysilicon film having a thickness of about 1 μm is laminated and formed. Next, patterning is performed by a normal photolithography method to form a first membrane layer 4 having a first slit 3 having a width of about 1 to 2 μm (FIG. 1).

After that, the first slit 3 is not filled with the oxide film 5, and the conductivity is about 0.08 μm thick on the first membrane layer 4 and the thermal oxide film 2 exposed in the first slit 3. A polysilicon film is laminated and formed. Next, patterning is performed by a normal photolithography method to form a second membrane layer 7 in which a second slit 6 having a width of about 0.1 to 0.2 μm is arranged in the first slit 3 (FIG. 7). ..

By forming the second slit 6 without filling the inside of the first slit 3 with the oxide film 5 in this way, the manufacturing process can be shortened.

Next, as in the first embodiment, the sacrificial layer 9 made of a USG film having a thickness of about 2.0 to 4.0 μm is laminated on the movable electrode 8 made of the first membrane layer 4 and the second membrane layer 7. To do. At this time, since the step formed by the first slit 3 and the second slit 6 is sufficiently smaller than the thickness of the sacrificial layer 9, it can be flattened only by forming the sacrificial layer 9. Hereinafter, according to the same manufacturing process as in the first embodiment, the MEMS device having the structure shown in FIG. 8 can be formed.

In the slit of the present embodiment formed in this way, as shown in FIG. 8B, a narrow second slit 6 is arranged in the wide first slit 3, and the narrow second slit 6 is arranged. The slit 6 of 2 makes it possible to suppress a decrease in low frequency sensitivity. Further, since the movable electrode 8 is composed of the thick first membrane layer 4 and the thin second membrane layer 7, the thin first membrane layer 4 can reinforce the thin second membrane layer 7. , It becomes possible to give strength to the movable electrode 8.

Next, a third embodiment of the present invention will be described. 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 conductivity having a thickness of about 0.08 μm is formed on the thermal oxide film 2 by a CVD method. Laminates a polysilicon film. Next, patterning is performed by a normal photolithography method to form a second membrane layer 7 having a second slit 6 having a width of about 0.1 to 0.2 μm (FIG. 9).

After that, on the thermal oxide film 2 exposed on the second membrane layer 7 and in the second slit 6, the oxide film 16 having a thickness of about 0.01 to 0.05 μm (in the third insulating film) by the CVD method. Equivalent) is laminated. Here, the oxide film 16 does not need to be flattened as shown in FIG. 10 (b). This is because the patterning of the first membrane layer 4 formed thereafter does not require miniaturization. The oxide film 16 functions as an etching stopper for the first membrane layer 4. Next, a conductive polysilicon film having a thickness of about 1 μm is laminated and formed on the oxide film 16 by a CVD method. Then, patterning is performed by a normal photolithography method to form a first membrane layer 4 having a first slit 3 having a width of about 1 to 2 μm on the upper portion of the second slit 6 (FIG. 10).

Next, as in the first embodiment, the sacrificial layer 9 made of USG having a thickness of about 0.2 to 4.0 μm is laminated on the movable electrode 8 made of the second membrane layer 7 and the first membrane layer 4. To do. At this time, since the step formed by the second slit 6 and the first slit 3 is sufficiently smaller than the thickness of the sacrificial layer 9, it can be flattened only by forming the sacrificial layer 9. Hereinafter, as in the first and second embodiments, the through hole 13 is formed to expose the sacrificial layer 9 in the through hole 13. After that, the silicon substrate 1 is removed from the back surface side of the silicon substrate 1 until the thermal oxide film 2 is exposed to form the back chamber 14 (corresponding to FIG. 5).

After that, by removing a part of the sacrificial layer 9 through the through hole 13 formed in the nitride film 12 and the fixed electrode 10, an air gap structure in which the fixed electrode 10 and the movable electrode 8 are fixed by the spacer 15 is formed. .. By this etching, a part of the thermal oxide film 2 and the oxide film 16 exposed in the first slit 3 are also removed (FIG. 11b). As a result, the second slit 6 and the first slit 3 are opened (FIG. 11a).

By forming the first slit 6 without filling the inside of the second slit 6 with the oxide 16 in this way, the manufacturing process can be shortened.

Further, as in the slit of the present embodiment, as shown in FIG. 11B, the wide first slit 3 is arranged on the narrow second slit 6, and the slit shown in the first embodiment. Even if the arrangement is reversed, the narrow second slit 6 can suppress the decrease in low frequency sensitivity, and the thick first membrane layer 4 can reinforce the thin second membrane layer 7. It becomes.

Next, a fourth embodiment of the present invention will be described. First, as in the third embodiment, 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 a thermal oxide film 2 having a thickness of about 1 μm is formed on the thermal oxide film 2 by a CVD method. A conductive polysilicon film having a thickness of about 0.08 μm is laminated and formed. Next, patterning is performed by a normal photolithography method to form a second membrane layer 7 having a second slit 6 having a width of about 0.1 to 0.2 μm (FIG. 9).

After that, on the thermal oxide film 2 exposed on the second membrane layer 7 and in the second slit 6, the oxide film 16 having a thickness of about 0.01 to 0.05 μm (in the third insulating film) by the CVD method. Equivalent) is laminated. Next, a conductive polysilicon film having a thickness of about 1 μm is laminated and formed on the oxide film 16 by a CVD method. Then, patterning is performed by a normal photolithography method to form a first membrane layer 4 having a first slit 3 having a width of about 1 to 2 μm on the upper portion of the second slit 6 (FIG. 10).

Next, an oxide film is laminated and formed on the first membrane layer 4 by a CVD method, and the inside of the first slit 3 is embedded with an oxide film 17 (also corresponding to a third insulating film) to be flattened. Next, the oxide film 17 on the first membrane layer 4 is removed, the oxide film 17 is left in the second slit 6 and the first slit 3, and the first membrane layer 4 is exposed. Then, a conductive polysilicon film having a thickness of about 0.08 μm is laminated on the flattened first membrane layer 4. Next, a third slit 18 (corresponding to the second slit) having a width of about 0.1 to 0.2 μm is provided on the oxide film 17 which is patterned by a normal photolithography method and embedded in the first slit 3. A third membrane layer 19 (corresponding to the second membrane layer) is formed (FIG. 12).

Hereinafter, as in the first embodiment, a USG film having a thickness of about 2.0 to 4.0 μm is placed on the movable electrode 8 composed of the second membrane layer 7, the first membrane layer 4, and the third membrane layer 19. The sacrificial layer 9 made of the material is laminated. After that, the silicon substrate 1 is removed from the back surface side of the silicon substrate 1 until the thermal oxide film 2 is exposed, and the back chamber 14 is formed.

After that, by removing a part of the sacrificial layer 9 through the through hole 13 formed in the nitride film 12 and the fixed electrode 10, an air gap structure in which the fixed electrode 10 and the movable electrode 8 are fixed by the spacer 15 is formed. .. By this etching, a part of the thermal oxide film 2, the oxide film 17 exposed in the third slit 18, and the oxide film 16 exposed by the removal of the oxide film 17 are removed (FIG. 13a). As a result, the third slit 18, the first slit 3 and the second slit 6 are opened (FIG. 13b).

As described above, in the slit of the present embodiment, as shown in FIG. 13B, the wide first slit 3 is arranged on the narrow second slit 6, and the narrower third slit 3 is further arranged. 18 is arranged, and the narrow second slit 6 and the third slit 18 make it possible to suppress a decrease in low frequency sensitivity. Further, since the thick first membrane layer 4 can reinforce the thin second membrane layer 7 and the third membrane layer 19, it is possible to give the movable electrode 8 strength.

1: Silicon substrate, 2: Thermal oxide film, 3: 1st slit, 4: 1st membrane layer, 5: oxide film, 6: 2nd slit, 7: 2nd membrane layer, 8: movable electrode , 9: sacrificial layer, 10: fixed electrode, 11: wiring film, 12: nitride film, 13: through hole, 14: back chamber, 15: spacer, 16: oxide film, 17: oxide film, 18: third Slit, 19: 3rd membrane layer, 20: Slit, 21: Air gap

Claims (3)

In a 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 substrate with a spacer interposed therebetween.
The movable electrode is composed of at least a first membrane layer and a second membrane layer thinner than the first membrane layer, and a plurality of slits penetrating the first membrane layer and the second membrane layer are formed. What you are doing
The slits are arranged so that the first slit formed on the first membrane layer and the second slit formed on the second membrane layer overlap each other.
A MEMS device characterized in that the width of the second slit is narrower than the width of the first slit. In a method for manufacturing a MEMS element in which a fixed electrode and a movable electrode are arranged with a spacer interposed therebetween on a substrate provided with a back chamber.
The step of forming the first insulating film on the surface of the substrate and
On the first insulating film, a first membrane layer having a first slit or a second membrane thinner than the first membrane layer having a second slit having a width narrower than the width of the first slit. The process of forming the layer and
The second membrane layer is formed on the first membrane layer, or the first membrane layer is formed on the second membrane layer, and the first membrane layer and the second membrane layer are formed. And the process of forming a movable electrode including
A step of forming a second insulating film on the movable electrode and
The step of forming the fixed electrode on the second 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 substrate to form the back chamber, and
A part of the second insulating film is removed by etching from the through hole to form the spacer, an air gap is formed between the fixed electrode and the movable electrode, and at the same time, one of the first insulating films. A method for manufacturing a MEMS element, which comprises a step of removing a portion and forming the movable electrode in which the first slit and the second slit communicate with each other. In the method for manufacturing a MEMS device according to claim 2.
In the step of forming the movable electrode including the second membrane layer on the first membrane layer, the second membrane layer is formed after filling the first slit with the third insulating film. Including the process
In the step of forming the movable electrode, at the same time as forming the air gap, a part of the first insulating film and the third insulating film are removed, and the first slit and the second slit are formed. A method for manufacturing a MEMS element, which comprises a step of forming the movable electrode to be communicated with.

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