How to evaluate MEMS devices

Abstract

To provide a method for evaluating micro electro mechanical systems (MEMS) devices that can reduce the time for measuring the size or mutual distance of fine pores formed in large numbers.SOLUTION: A method for evaluating micro electro mechanical systems (MEMS) devices includes a measurement step for capturing a predetermined region of a wafer surface with a camera, and detecting, from an image including a plurality of pores 120 (captured image 201), and coordinates of the outer rims of the pores 120 by image processing, to measure the diameters 123 of each pore 120 and a distance 124 between the pores 120; and a pass / fail determination step for determining whether values measured by the measurement step fall within preset allowable ranges of the diameter 123 and distance 124.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a method for evaluating a MEMS device. [Background technology]

[0002] 2. Description of the Related Art MEMS (Micro Electro Mechanical Systems) are known, which are formed by etching a silicon wafer to form thin films or recesses and are used to produce various sensors, printer heads, mirror devices, and the like (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-170851 A Summary of the Invention [Problem to be solved by the invention]

[0004] Among MEMS, development is underway to use plasma etching technology to create a large number of minute holes in a small area to form sensors, microphones, etc. In order to evaluate the results of processing these holes, it is necessary to measure the size and distance of the holes, but there is a problem in that measuring each and every hole takes an enormous amount of time.

[0005] The present invention has been made in consideration of such problems, and its object is to provide a method for evaluating MEMS devices that can reduce the time required to measure the size and distance of minute pores formed in large quantities. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the objective, the MEMS device evaluation method of the present invention is a method for evaluating a MEMS device in which a plurality of pores are formed by plasma etching in a predetermined region on the surface of a wafer, and includes a measurement step of photographing the predetermined region on the surface of the wafer with a camera, detecting the coordinates of the outer edges of the plurality of pores from the image of the plurality of pores by image processing, and measuring the diameter and distance of each of the pores, and a pass / fail judgment step of determining whether the values ​​measured in the measurement step fall within a predetermined tolerance range for the diameter and distance.

[0007] The diameter of the pores and the distance may be 0.5 mm or less. Effect of the Invention

[0008] The present invention can reduce the time required to measure the size and distance of minute pores formed in large quantities. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view showing an example of the configuration of a MEMS device to be evaluated by a MEMS device evaluation method according to an embodiment. [Diagram 2] FIG. 2 is a perspective view showing details of the MEMS device of FIG. [Diagram 3] FIG. 3 is a cross-sectional view showing details of the MEMS device of FIG. [Figure 4] FIG. 4 is a cross-sectional view showing an example of the configuration of an evaluation apparatus for performing the MEMS device evaluation method according to the embodiment. [Diagram 5] FIG. 5 is a flowchart showing a processing procedure of the MEMS device evaluation method according to the embodiment. [Figure 6] FIG. 6 is a diagram for explaining the measurement steps of FIG. [Figure 7] FIG. 7 is a diagram for explaining the measurement steps of FIG. [Figure 8] FIG. 8 is a diagram for explaining the measurement steps of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The form (embodiment) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiment. Furthermore, the components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the configurations described below can be appropriately combined. Furthermore, various omissions, substitutions, or modifications of the configurations can be made without departing from the gist of the present invention.

[0011] [Embodiment] A method for evaluating a MEMS (Micro Electro Mechanical Systems) device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing an example of the configuration of a MEMS device 110 that is an evaluation target evaluated by the method for evaluating a MEMS device according to an embodiment. FIG. 2 is a perspective view showing details of the MEMS device 110 in FIG. 1. FIG. 2 is an enlarged perspective view of a surface 111 of the MEMS device 110 in FIG. 1. FIG. 3 is a cross-sectional view showing details of the MEMS device 110 in FIG. 1. FIG. 3 is a cross-sectional view taken along the thickness direction of the MEMS device 110 in FIG. 1.

[0012] In the embodiment, a wafer (MEMS device wafer) 100 having a MEMS device 110 to be evaluated by the MEMS device evaluation method is, for example, a disk-shaped semiconductor device wafer or an optical device wafer made of silicon, sapphire, silicon carbide (SiC), gallium arsenide, or the like. As shown in FIG. 1, the wafer 100 has a plurality of division lines 102 formed in a lattice pattern on a flat surface 101, and the MEMS devices 110 are formed in the areas partitioned by the plurality of division lines 102. In the present embodiment, the wafer 100 has an adhesive tape 105 attached to a back surface 104 on the back side of the front surface 101, and an annular frame 106 attached to the outer edge of the adhesive tape 105, but the present invention is not limited to this. For example, the wafer 100 may be fixed to a hard substrate (substrate).

[0013] 2 and 3, the wafer 100 has a plurality of pores 120 formed in a predetermined region on the front surface 101 where the MEMS devices 110 are formed, i.e., a predetermined region on the front surface 111 of the MEMS devices 110. The plurality of pores 120 are all formed to have the same shape. As shown in FIG. 2, the pores 120 have openings 121 on the front surfaces 101, 111 formed to be circular in plan view, the openings 121 are sufficiently smaller than the front surface 111 of one MEMS device 110, and are formed to have a cylindrical shape whose depth does not penetrate to the rear surface 104 side of the wafer 100.

[0014] The pores 120 are formed, for example, by coating the entire surface of the front surface 101 of the wafer 100 with a predetermined protective film layer, irradiating a predetermined region where the pores 120 are to be formed with a laser beam to remove the protective film layer, and then digging the region from which the protective film layer has been removed in the depth direction by a Bosch process of plasma etching. Therefore, the pores 120 can be formed minutely and in large quantities on the front surface 111 of the MEMS device 110, as described below.

[0015] The multiple pores 120 are regularly arranged on the surface 111 of one MEMS device 110 such that the openings 121 of adjacent pores 120 are equally spaced from each other in a planar view. In this embodiment, the pores 120 are arranged in a lattice shape of equilateral triangles in a planar view on the surface 111 of the MEMS device 110 as shown in Fig. 2, but the present invention is not limited to this, and the pores 120 may be arranged in a lattice shape of a regular square or regular hexagon, etc.

[0016] As shown in FIG. 3, the MEMS device 110 includes a base material layer 115 and a device pattern layer 116. The device pattern layer 116 is formed on a back surface 114 behind the front surface 111, and the base material layer 115 is laminated on the front surface 111 side. The base material layer 115 is exposed on the front surface 111 side. In this embodiment, the front surface 111 side is the MEMS device 110, but the present invention is not limited to this, and the back surface 114 side may be the MEMS device 110. The device pattern layer 116 is formed in a thin film shape, sufficiently thinner than the base material layer 115. The pores 120 are formed penetrating the base material layer 115, and the back surface 114 side is blocked by the thin film device pattern layer 116. The MEMS device 110 detects vibrations of the thin film device pattern layer 116 at the locations where the pores 120 are formed, and converts the detected vibrations into predetermined information, which is called sensing. In such a MEMS device 110, the uniformity of the diameter 123 of the openings 121 of the pores 120 and the evenness of the distance 124 between the centers 122 of the openings 121 of the pores 120 greatly contribute to the sensing performance, so the diameter 123 of each pore 120 and the distance 124 between the centers 122 of the openings 121 are important evaluation items. The MEMS device 110 that performs such sensing is used, for example, in a sensor or a microphone.

[0017] In this embodiment, the MEMS device 110 is, for example, about 15 mm (15,000 μm) square in plan view and about 60 μm thick. In this embodiment, the base material layer 115 is about 50 μm thick, and the device pattern layer 116 is about 10 μm thick. Therefore, the depth of the pores 120 is, for example, 50 μm in this embodiment. In addition, the diameter 123 of the pores 120 formed in the MEMS device 110 and the distance 124 between adjacent pores 120 are both minute, 5 μm or more and 0.5 mm (500 μm) or less. In this embodiment, for example, the distance 124 between adjacent pores 120 is even minute, 150 μm or less, the diameter 123 of the pores 120 is a value slightly smaller than the distance 124 between the pores 120, and a large number of pores 120, about 12,000, are formed on the surface 111 of one MEMS device 110.

[0018] 4 is a cross-sectional view showing a configuration example of an evaluation apparatus (MEMS device evaluation apparatus) 1 for performing the MEMS device evaluation method according to the embodiment. In the embodiment, the evaluation apparatus 1 for performing the MEMS device evaluation method includes a holding table 10, a camera 20, and a control unit 30, as shown in FIG.

[0019] In this embodiment, the holding table 10 is a so-called chuck table having, for example, a disk-shaped frame body with a recess formed therein and a disk-shaped suction part fitted into the recess. Note that the holding table 10 is not limited to this in the present invention, and may be any table as long as it can hold and fix the wafer 100 with the front surface 101 exposed. The suction part of the holding table 10 is formed of a porous porous ceramic or the like, and is connected to a vacuum suction source (not shown) via a vacuum suction path (not shown). The upper surface of the suction part of the holding table 10 is a holding surface 11 on which the wafer 100 is placed and which suction-holds the placed wafer 100. In the first embodiment, the holding surface 11 is a holding surface on which the wafer 100 is placed with the front surface 101 facing upward, and suction-holds the placed wafer 100 from the back surface 104 side via an adhesive tape 105. The holding surface 11 and the upper surface of the frame body of the holding table 10 are arranged on the same plane and are formed parallel to a horizontal plane.

[0020] The camera 20 includes an imaging element that captures an image of a surface 111 of the MEMS device 110 formed on the wafer 100 held on the holding table 10, an opening 121 of a pore 120 formed on the surface 111, etc. The imaging element is, for example, a CCD (Charge-Coupled Device) imaging element or a CMOS (Complementary MOS) imaging element. In the first embodiment, the camera 20 moves relatively to the holding table 10 and the wafer 100 held on the holding table 10 by a moving unit (not shown).

[0021] The camera 20 has a field of view 21 with an area including the openings 121 of the multiple pores 120 in all directions in which the openings 121 of the pores 120 are arranged (arrangement direction). Therefore, the camera 20 can photograph the multiple pores 120 in all arrangement directions within one field of view 21, and can obtain an image including the multiple pores 120 in all arrangement directions (for example, image 201 shown in FIG. 6).

[0022] The control unit 30 controls the operation of each component of the evaluation apparatus 1 to cause the evaluation apparatus 1 to perform the evaluation method for a MEMS device according to the embodiment. In this embodiment, the control unit 30 includes a computer system. The computer system included in the control unit 30 includes an arithmetic processing device having a microprocessor such as a CPU (Central Processing Unit), a storage device having a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory), and an input / output interface device. The function of the control unit 30 is realized by the arithmetic processing device of the computer system performing arithmetic processing according to a computer program stored in the storage device of the computer system and outputting a control signal for controlling the evaluation apparatus 1 to each component of the evaluation apparatus 1 via the input / output interface device of the evaluation apparatus 1.

[0023] Next, this specification will explain the operation of the process of the MEMS device evaluation method according to the embodiment with reference to the drawings. Fig. 5 is a flowchart showing the process procedure of the MEMS device evaluation method according to the embodiment. Figs. 6, 7 and 8 are all diagrams explaining the measurement step 1001 of Fig. 5. The MEMS device evaluation method according to the embodiment is an example of an operation process performed by the evaluation apparatus 1, and includes a measurement step 1001 and a pass / fail determination step 1002 as shown in Fig. 5.

[0024] In the method for evaluating a MEMS device according to the embodiment, first, a wafer 100 having MEMS devices 110 to be evaluated is held on a holding surface 11 of a holding table 10 with a front surface 101 facing upward.

[0025] The measurement step 1001 is a step in which the control unit 30 photographs a specified area on the surface 101 of the wafer 100 in which the pores 120 are formed using the camera 20, detects the coordinates of the outer edges of the openings 121 of the pores 120 by image processing from the photographed image 201 (see Figure 6) in which a plurality of pores 120 are photographed, and measures the diameter 123 of each pore 120 and the distance 124 between the centers 122 of the openings 121 of the pores 120.

[0026] In the measurement step 1001, the control unit 30 first moves the camera 20 as shown in Fig. 4 to set the photographing field 21 of the camera 20 to a predetermined area where the pores 120 are formed on the surface 111 of the MEMS device 110 formed on the wafer 100 held on the holding table 10. In the measurement step 1001, the control unit 30 then photographs the camera 20 with the photographing field 21 set to a predetermined area, and obtains a photographed image 201 including a plurality of pores 120 as shown in Fig. 6. In the photographed image 201 photographed by the camera 20 in the measurement step 1001, in this embodiment, as shown in Fig. 6, the area inside the opening 121 of the pore 120 is photographed with high brightness, and the area of ​​the surface 111 of the MEMS device 110 where the pores 120 are not formed is photographed with low brightness.

[0027] In the measurement step 1001, the control unit 30 then performs binarization processing on the acquired photographed image 201 based on a predetermined luminance as shown in Fig. 6, thereby acquiring a binarized image 202. Here, in this embodiment, the predetermined luminance is sufficiently lower than the luminance of the region inside the opening 121 of the pore 120 and sufficiently higher than the luminance of the region of the surface 111 of the MEMS device 110 where the pore 120 is not formed. In the binarized image 202 acquired in the measurement step 1001, in this embodiment, as shown in Fig. 6, the region inside the opening 121 of the pore 120 is represented by a bright luminance, and the region of the surface 111 of the MEMS device 110 where the pore 120 is not formed is represented by a dark luminance.

[0028] In the present invention, the captured image 201 captured by the camera 20 in the measuring step 1001 and the binarized image 202 obtained by binarization are not limited to the above-mentioned forms, and the brightness of the area inside the opening 121 of the pore 120 and the brightness of the area on the surface 111 of the MEMS device 110 where the pore 120 is not formed may be reversed. In this case, in the measuring step 1001, the control unit 30 performs binarization based on a brightness that is sufficiently higher than the brightness of the area inside the opening 121 of the pore 120 and sufficiently lower than the brightness of the area on the surface 111 of the MEMS device 110 where the pore 120 is not formed. Also, the captured image 201 may be image-processed without being binarized to detect the pore 120.

[0029] In the measurement step 1001, the control unit 30 detects the coordinates of the boundary between bright luminance and dark luminance in the acquired binary image 202 as the coordinates of the outer periphery of the opening 121 of the pore 120. In the measurement step 1001, the control unit 30 detects the coordinates of the outer periphery of the opening 121 of the pore 120 for all the pores 120 in the captured image 201 and the binary image 202. In the measurement step 1001, the control unit 30 then calculates the coordinates of the center 122 of the opening 121 of each pore 120 based on the detected coordinates of the outer periphery of the opening 121 of each pore 120.

[0030] In the measurement step 1001, the control unit 30 calculates the diameter 123 of the opening 121 of each pore 120 based on the coordinates of the outer periphery of the opening 121 of each pore 120 and the coordinates of the center 122 of the opening 121 of each pore 120. In this embodiment, specifically, as shown in Fig. 7, the control unit 30 calculates a circle inscribed and circumscribed on the curve of the coordinates of the outer periphery of the opening 121 of each pore 120, calculates the diameter of the inscribed circle 125 as the minimum hole diameter of the opening 121, and calculates the diameter of the circumscribed circle 126 as the maximum hole diameter of the opening 121, and calculates an average hole diameter, for example, by averaging based on the minimum hole diameter and the maximum hole diameter, and sets this calculated average hole diameter as the diameter 123 of the opening 121 of each pore 120. In the measuring step 1001, the diameter 123 of the evaluation object is the average hole diameter in this embodiment, but the present invention is not limited to this, and the diameter 123 of the evaluation object may be the minimum hole diameter or the maximum hole diameter. In the measuring step 1001, the control unit 30 may also generate distribution data of the calculated diameter 123 of the opening 121 of each fine hole 120. In the measuring step 1001, the control unit 30 may further calculate the roundness and its distribution data, which are calculated as half the difference between the maximum hole diameter and the minimum hole diameter of the opening 121 of each fine hole 120, based on the minimum hole diameter and the maximum hole diameter, and the roundness may also be evaluated.

[0031] Moreover, in the measuring step 1001, the control unit 30 calculates each distance 124 between the centers 122 of the openings 121 of adjacent pores 120 based on the coordinates of the centers 122 of the openings 121 of each pore 120, as shown in Fig. 7. In the measuring step 1001, the control unit 30 may further generate distribution data of each calculated distance 124 between the centers 122 of the openings 121 of adjacent pores 120, as shown in Fig. 8.

[0032] In the pass / fail determination step 1002, the control unit 30 determines whether the values ​​measured in the measurement step 1001 fall within the preset allowable ranges of the diameter 123 and the distance 124. Here, the allowable range refers to a range equal to or greater than a predetermined upper limit and equal to or less than a predetermined lower limit (a value greater than the upper limit), and is the range of diameters of the multiple pores 120 within which the MEMS device 110 can exhibit the required performance, such as sensing. The control unit 30 stores the allowable range data of the diameter 123 and the distance 124 set in advance. In the pass / fail determination step 1002, if all the diameters 123 measured in the measurement step 1001 are within the preset allowable ranges of the diameters 123 and the distances 124 measured in the measurement step 1001 are within the preset allowable ranges of the distances 124, the control unit 30 determines that the MEMS device 110 whose diameters 123 and distances 124 are measured is pass (pass). On the other hand, in pass / fail determination step 1002, if at least one of the diameters 123 measured in the measurement step 1001 is outside the preset tolerance range for the diameters 123, or if at least one of the distances 124 measured in the measurement step 1001 is outside the preset tolerance range for the distances 124, the control unit 30 determines that the MEMS device 110 whose diameters 123 and distances 124 are measured is unsatisfactory (failed). In pass / fail determination step 1002, it may further be determined whether the circularity of the openings 121 of the pores 120 falls within a preset tolerance range.

[0033] In pass / fail determination step 1002, if the control unit 30 determines that the MEMS device 110 whose diameter 123 and distance 124 have been measured has failed, it may calculate the percentage of the diameters 123 measured in measurement step 1001 that are outside the predetermined tolerance range for the diameters 123, or the percentage of the distances 124 measured in measurement step 1001 that are outside the predetermined tolerance range for the distances 124.

[0034] In the pass / fail determination step 1002, the present invention is not limited to this, and the control unit 30 may determine that the MEMS device 110 whose diameters 123 and distances 124 are measured is pass (pass) when all of the diameters 123 measured in the measurement step 1001 are within a preset tolerance range of the diameters 123 or all of the distances 124 measured in the measurement step 1001 are within a preset tolerance range of the distances 124, and may determine the other cases as fail (fail). That is, in the pass / fail determination step 1002, the control unit 30 may determine that the MEMS device 110 whose diameters 123 and distances 124 are measured is pass (pass) when at least one of the cases where all of the diameters 123 measured in the measurement step 1001 are within a preset tolerance range of the diameters 123 and the cases where all of the distances 124 measured in the measurement step 1001 are within a preset tolerance range of the distances 124, and may determine the other cases as fail (fail).

[0035] In addition, in the pass / fail determination step 1002, in the present invention, the control unit 30 may determine that the MEMS device 110 whose diameters 123 and distances 124 are measured is pass (success) if the ratio of each diameter 123 measured in the measurement step 1001 that is within the preset allowable range of the diameter 123 is equal to or greater than a preset predetermined ratio, and further determine that the ratio of each distance 124 measured in the measurement step 1001 that is within the preset allowable range of the distance 124 is equal to or greater than a preset predetermined ratio, and may determine that the MEMS device 110 is fail (fail) in other cases. Here, the predetermined ratio is, for example, 90%, 95%, 99%, etc. In addition, in the pass / fail determination step 1002, in the present invention, the control unit 30 may determine that the MEMS device 110 whose diameters 123 and distances 124 were measured is pass (success) if the percentage of each diameter 123 measured in the measurement step 1001 that is within a preset tolerance range of the diameters 123 is equal to or greater than a preset predetermined percentage, or the percentage of each distance 124 measured in the measurement step 1001 that is within a preset tolerance range of the distances 124 is equal to or greater than a preset predetermined percentage, and may determine that the MEMS device 110 whose diameters 123 and distances 124 were measured is fail (fail) in other cases.

[0036] After performing the measurement step 1001 and the pass / fail determination step 1002, the control unit 30 may display, on a display unit (not shown) provided in the evaluation apparatus 1, the evaluation results of the MEMS device evaluation method, such as distribution data of each diameter 123 and each distance 124 measured in the measurement step 1001, the determination result in the pass / fail determination step 1002, and the percentage of each diameter 123 and each distance 124 that is outside the allowable range calculated when a fail determination is made in the pass / fail determination step 1002.

[0037] The method for evaluating a MEMS device according to the embodiment having the above-mentioned configuration captures a plurality of pores 120 formed on the surface 111 of the MEMS device 110 in one image, detects the plurality of pores 120 at once using an image processing technique, determines the center 122 of the opening 121 of each pore 120, measures the diameter 123 of the opening 121 of each pore 120, and measures the distance 124 between the centers 122, thereby quantitatively evaluating the plurality of pores 120 under the same measurement conditions. Therefore, the method for evaluating a MEMS device according to the embodiment can detect a large number of pores 120 at once from one image and measure the diameter 123 and distance 124 of each pore 120 at once, the more minute the pores 120 formed on the surface 111 of the MEMS device 110 are and the greater the number of pores formed. Therefore, the method for evaluating a MEMS device according to the embodiment has an effect of significantly reducing the time required to measure the size (diameter 123) and distance 124 of the fine pores 120 formed in large quantities on the surface 111 of the MEMS device 110.

[0038] Moreover, the MEMS device 110 in which the pores 120, which are the evaluation target of the MEMS device evaluation method according to the embodiment, are formed includes a base material layer 115 and a thin-film device pattern layer 116 which is thinner than the base material layer 115, the pores 120 are formed penetrating the base material layer 115, and the back surface 114 side is blocked by the thin-film device pattern layer 116, and sensing is performed at the location where the pores 120 are formed. Therefore, the MEMS device evaluation method according to the embodiment can quantitatively evaluate important quality items such as uniformity of diameters 123 of openings 121 of the pores 120 and equality of distances 124 between centers 122 of the openings 121 of the pores 120, which greatly contribute to the sensing performance of the MEMS device 110, in a short time under the same measurement conditions.

[0039] The present invention is not limited to the above embodiment. In other words, various modifications can be made without departing from the gist of the present invention. For example, the measurement object may be a pore penetrating not only the base material layer of the wafer but also a thin-film device pattern layer, or a through hole formed in a wafer without a device pattern layer or a pore consisting of a non-penetrating depression. [Explanation of symbols]

[0040] 1. Evaluation device 20 Camera 30 Control Unit 100 wafers 101,111 surface 110 MEMS Devices 120 pores 123 diameter 124 distance

Claims

1. A method for evaluating a MEMS device in which a plurality of pores are formed in a predetermined region on a surface of a wafer by plasma etching, the method comprising the steps of: a measuring step of photographing the predetermined area on the surface of the wafer with a camera, detecting the coordinates of the outer periphery of the plurality of pores from the photographed image by image processing, and measuring the diameter of each of the pores and the distance between the pores; a pass / fail determination step for determining whether or not the value measured in the measurement step falls within a preset allowable range of the diameter and the distance; A method for evaluating a MEMS device comprising:

2. 2. The method for evaluating a MEMS device according to claim 1, wherein the diameter of the hole and the distance are 0.5 mm or less.

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