JP2017121028A - MEMS element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure of a MEMS element for preventing breakage of a film while improving sensitivity of the MEMS element.SOLUTION: A plurality of slits 4a and 4b are formed adjacently to a movable electrode 3 (diaphragm film), and have a shape having an opening shape with a slit width widened on a side opposite to the opposing slit.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a MEMS element, and more particularly to a capacitive MEMS element used as a microphone, various sensors, switches, and the like.

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

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

  Generally, in order to increase the sensitivity of a condenser microphone, it is necessary to increase the displacement of the movable electrode due to sound pressure. Therefore, a slit is formed on the outer periphery of the movable electrode so as to narrow the area supporting the movable electrode by extending a slit extending from the outer peripheral side toward the center, or a slit is formed along the outer periphery of the movable electrode as shown in FIG. The method (Patent Document 1) is generally used. On the other hand, if the slit width is too wide, the low frequency sensitivity is lowered. In addition, if the slit width is too narrow, stress concentrates on the slit end, which causes damage to the movable electrode.

  Therefore, in the case of narrowing the slit width, a method of adjusting the stress concentration by a method of forming a circular opening shape having a diameter larger than the slit width at the slit end has been proposed. FIG. 4 is an explanatory view of the slit structure of this type of MEMS element. As shown in FIG. 4, two slit rows are formed in the diaphragm film 3 and are arranged in a staggered manner so that their ends do not overlap each other. A substantially circular opening shape is formed at the end of the slit.

Japanese Patent Laid-Open No. 2007-210083

  By the way, when the slit 4 having a circular opening shape having a diameter larger than the slit width is formed at the slit end in the diaphragm film 3, the circular opening shape is disposed between the slit rows. Therefore, there is a problem that stress concentration occurs in a region where the dimension between the circular opening shape and the adjacent slit row becomes narrow, and the slit row is damaged. In order to solve such problems, an object of the present invention is to provide a MEMS element capable of improving the low frequency sensitivity of the MEMS element and reducing stress concentration between slits.

  In order to achieve the above object, according to the first aspect of the present invention, an air gap is formed by arranging a substrate having a back chamber and a fixed electrode and a movable electrode on the substrate with a spacer interposed therebetween. In the MEMS element, a plurality of slits are formed in the movable electrode, and the slits include a first slit composed of at least one slit disposed along a connection end with the spacer, and the first slit. A second slit comprising at least one slit disposed inside the slit, and at least one of the first slits is a slit closer to the spacer than an extension line of the slit at an opening end. An opening shape that is partitioned into a shape having an expanded curvature is provided, and at least one of the second slits extends to the opening end. Characterized in that it has a than the spacers side opening shape that is defined in a shape having a curvature expand the slit width on the opposite side of the line.

  Since the MEMS element of the present invention can form slits along the outer periphery of the movable electrode, the influence of sensitivity due to residual stress can be reduced, and a MEMS element with little variation in sensitivity can be supplied.

  Moreover, the MEMS element of this invention makes the dimension between slit row | line | columns substantially constant by setting it as the shape provided with the opening shape which expanded the slit width on the opposite side to the slit which opposes the shape of a slit. For this reason, it becomes possible to relieve the stress concentration at the slit end and prevent the movable electrode from being damaged. In particular, in order to improve the low frequency sensitivity, even when the slit width is narrowed, the stress is not concentrated on the slit end, and the effect is great.

It is explanatory drawing of the manufacturing process of the MEMS element of this invention. (A) is a figure explaining the slit structure of the MEMS element of the Example of this invention. (B) is an enlarged view of the A section shown in (a). It is a figure explaining the slit structure of the conventional MEMS element. (A) is a figure explaining the slit structure of the conventional MEMS element. (B) is an enlarged view of the A section shown in (a).

  In the MEMS element according to the present invention, at least two or more slits are formed adjacent to the movable electrode, and the movable electrode is damaged by providing a desired opening shape at the outer end of the facing slit. It becomes possible to prevent. Examples of the present invention will be described below by taking a condenser microphone as an example of the MEMS element.

  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 of 420 μm, and a thickness of 0 is formed on the thermal oxide film 2 by a CVD (Chemical Vapor Deposition) method. A 4 μm conductive polysilicon film is laminated. Next, patterning is performed by a normal photolithographic method to form a diaphragm film 3 to be a movable electrode (FIG. 1a). Here, according to the present invention, as will be described later, the diaphragm 4 is formed in the diaphragm film 3 for relaxing stress concentration between the slits.

  Thereafter, in accordance with a normal manufacturing process, a sacrificial layer 5 made of a USG (Undoped Silicate Glass) film having a thickness of about 2.0 to 4.0 μm is laminated on the diaphragm film 3, and the sacrificial layer 5 is further thickened. A conductive polysilicon film having a thickness of about 0.1 to 1.0 μm is stacked. Next, patterning is performed by a normal photolithographic method to form a fixed electrode film 6 in a stacked manner (FIG. 1b).

  A part of the sacrificial layer 5 is removed by etching, and a part of the diaphragm film 3 previously formed is exposed. At this time, the scribe line is also opened. A wiring film 7 made of a conductor film such as aluminum connected to the exposed diaphragm film 3 and fixed electrode 6 is formed (FIG. 1c).

  After the nitride film 8 is deposited on the entire surface, a through hole 9 for transmitting the sound pressure to the diaphragm film 3 is formed by a normal photolithographic method, and the sacrificial layer 5 is exposed in the through hole 9. Thereafter, 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 a back chamber 10 is formed (FIG. 1d).

  Thereafter, the fixed electrode film 6 and the diaphragm film 3 are fixed to the spacer 11 formed by removing a part of the sacrificial layer 5 through the through-holes 9 formed in the nitride film 8 and the fixed electrode film 6, and the air gap structure is formed. It is formed. By this etching, part of the thermal oxide film 2 is also removed, and the diaphragm film 3 in which the slits 4 are formed is exposed (FIG. 1e).

  Next, the shape of the slit 4 will be described. The slit 4 of the MEMS element of the present invention has an opening shape partitioned into a shape having a curvature with the slit width widened outward from the extension line at the opening end of each of the opposing slits. It is characterized by that. A specific example is shown in FIG. FIG. 2 schematically shows the diaphragm film 3 in which the slits 4 are formed from the fixed electrode side 6.

  The diaphragm film 3 has two slit rows. Of the two slit rows, one slit 4a of the slit row formed on the spacer 11 side has a substantially circular pattern at the end on the spacer side, and 4b of the slit row formed on the inside thereof is a spacer A substantially circular pattern is provided at the end opposite to the side. When formed in this way, the dimension between the slit rows is substantially constant over the entire circumference. For this reason, stress is not concentrated on the slit end, and the diaphragm film 3 can be prevented from being damaged.

  When three or more slit rows are formed, the slit row closest to the spacer and the slit row farthest from the spacer (closest to the center of the diaphragm film 3) may have such a shape.

  In addition, although the case where the opening shape of the slit end portion is formed in a substantially circular shape has been described as an example, the present invention is not limited to this, and any shape having a curvature may be used. For example, a rectangular shape having a drop shape and a curvature may be formed.

1: silicon substrate, 2: thermal oxide film, 3: diaphragm film, 4: slit, 5: sacrificial layer, 6: fixed electrode film, 7: wiring film, 8: nitride film, 9: through hole, 10: back chamber , 11: Spacer

Claims (1)

In a MEMS element in which an air gap is formed by arranging a substrate having a back chamber and a fixed electrode and a movable electrode on the substrate with a spacer interposed therebetween,
A plurality of slits are formed in the movable electrode,
The slit includes a first slit composed of at least one slit disposed along a connection end with the spacer, and a first slit composed of at least one slit disposed inside the first slit. With two slits,
At least one of the first slits has an opening shape partitioned into a shape having a curvature in which the slit width is widened toward the spacer side from the extension line of the slit at the opening end, and the second slit At least one of the slits has an opening shape that is partitioned into a shape having a curvature in which the slit width is widened to the opposite side to the spacer side from the extension line of the slit at the opening end. MEMS element to do.

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