JP6154290B2 - Composite board - Google Patents

Description

  The present invention relates to a composite substrate having a functional layer.

  In recent years, composite substrates in which substrates made of different materials are bonded have been developed. Such a composite substrate assumes that a functional element is formed on at least one substrate.

An example of the composite substrate is an SOS (Silicon On Sapphire) structure. As a method for forming this SOS structure, for example, a technique described in Patent Document 1 is known. According to the technique described in Patent Document 1, a composite substrate in which a silicon layer is epitaxially grown on the entire surface of a flat sapphire substrate can be obtained.

Japanese Patent Laid-Open No. 10-12547

  However, the composite substrate having the SOS structure described in Patent Document 1 is easily damaged by external impact during handling, and there is a risk that the silicon layer as a functional layer is damaged and the productivity is lowered. In addition, when a functional element is formed, the cleaning liquid, resist, and the like cannot be uniformly held on the silicon layer, and there is a concern that the yield may be lowered.

  The present invention has been conceived under the above-described circumstances, and an object thereof is to provide a composite substrate having high productivity and high yield.

  The composite substrate of the present invention has a central part and a peripheral part, and the peripheral part has an upper surface located below the upper surface of the central part in a side view, and a thickness thereof is larger than that of the central part. And a support substrate that is thin and has an acute angle α formed between the upper surface of the peripheral portion and the side surface of the central portion, and a functional layer positioned on the central portion of the support substrate.

  According to the present invention, it is possible to provide a composite substrate with high productivity and high yield by suppressing damage to the functional layer from external impact.

(A) is a top view which shows schematic structure of one Embodiment of the composite substrate concerning this invention, (b) is sectional drawing along the Ib-Ib line | wire shown to (a). (A) is a top view which shows schematic structure of one Embodiment of the composite substrate which concerns on this invention, (b) is sectional drawing along the IIb-IIb line | wire shown to (a). (A) is a top view which shows schematic structure of one Embodiment of the composite substrate based on this invention, (b) is sectional drawing along the IIIb-IIIb line | wire shown to (a). It is a diagram which shows the shape measurement result in a functional layer outer peripheral part.

<First Embodiment of Composite Substrate>
A composite substrate 1 which is an example of an embodiment of a composite substrate of the present invention will be described with reference to the drawings. The composite substrate 1 shown in FIG. 1 includes a support substrate 10 and a functional layer 20.

  The type of the support substrate 10 is not particularly limited as long as it can hold the functional layer 20 positioned on the upper side, and a semiconductor substrate, a piezoelectric substrate, a single crystal substrate, a resin substrate, a glass substrate, or the like can be used. In this embodiment, an example using a single crystal substrate which is an insulating material will be described. Specifically, it is formed of an aluminum oxide single crystal (hereinafter referred to as “sapphire”).

  The support substrate 10 has a central portion 11 located at the center and a peripheral portion 12 located at the periphery thereof. The peripheral edge portion 12 is disposed so as to surround the central portion 11. Here, the “center” indicates a relative positional relationship between the central portion 11 and the peripheral edge portion 12, and does not indicate an absolute positional relationship with respect to the entire support substrate 10. That is, the “center” of the support substrate 10 and the “center” of the central portion 11 do not necessarily coincide with each other.

  The upper surface 12 a of the peripheral edge portion 12 is positioned below the upper surface 11 a of the central portion 11. In this example, the lower surface 11b of the central portion 11 and the lower surface 12b of the peripheral edge portion 12 are aligned and are located on the same plane. Further, the thickness d2 of the support substrate 10 in the peripheral portion 12 is thinner than the thickness d1 in the central portion 11. Although the thickness d1 in the center part 11 will not be specifically limited if the functional layer 20 located in the upper part can be supported, For example, what is necessary is just to be about 600 micrometers-650 micrometers. The thickness d2 at the peripheral edge portion 12 may be, for example, about d1−d2> 10 μm. The support substrate 10 may have a chamfered outer peripheral portion to prevent chipping. In this case, the thickness d2 of the peripheral edge 12 is measured between the upper surface 12a and the lower surface 12b that are parallel to each other. Similarly, the thickness d1 of the central portion 11 is measured between the upper surface 11a and the lower surface 11b that are parallel to each other.

  Further, an angle α formed between the side surface of the central portion 11 of the support substrate 10 and the upper surface 12a of the peripheral edge portion 12 is an acute angle. In other words, the lower surface 11b of the central portion 11 has a larger area than the upper surface 11a, and the side surface of the central portion 11 forms an inclined surface so as to spread from the upper surface 11a toward the upper surface 12a of the peripheral edge portion 12. In the example illustrated in FIG. 1, the cross-sectional shape of the central portion 11 is a trapezoid when the support substrate 10 is viewed in cross section, but the present invention is not limited to this. For example, the line connecting the end portion 11e of the upper surface 11a of the central portion 11 to the end portion 12e on the side close to the central portion 11 of the upper surface 12a of the peripheral edge portion 12 is not limited to a straight line, and is convex upward or convex downward It may be a curve. The angle α is not particularly limited as long as it is an acute angle, but may be, for example, 10 ° to 45 °.

  In general, the angle α is a straight line connecting the end portion 11e of the upper surface 11a of the central portion 11 and the end portion 12e of the upper surface 12a of the peripheral portion 12 when the support substrate 10 is viewed in cross section. An angle formed by an extension line of the upper surface 12a of the portion 12 is obtained. However, this is not the case when the line connecting the end portion 11e to the end portion 12e is a curve or a line having a refracting portion. In the case of a curved line, an angle formed by a tangent line in the vicinity of the end 12e of the curved line and an extension line of the upper surface 12a of the peripheral edge 12 is defined as an angle α. In the case of a line having a refracting portion, an angle α is an angle formed by a line connecting the refracting portion closest to the end portion 12e and the end portion 12e and an extension line of the upper surface 12a of the peripheral edge portion 12.

  The functional layer 20 is supported and bonded to the upper surface 11 a of the central portion 11 of the support substrate 10. In this example, the functional layer 20 is disposed so as to cover the entire upper surface 11 a of the central portion 11. In other words, the upper surface 11a of the central portion 11 and the lower surface of the functional layer 20 are arranged to be aligned. Examples of the thickness of the functional layer 20 include a range of 50 to 300 [nm].

  The functional layer 20 can have a desired function by, for example, making a semiconductor element, and various materials can be selected depending on the desired function. For example, a material having a coefficient of thermal expansion opposite to that of the support substrate 10 may be selected as a temperature compensation film, or a dielectric material or a piezoelectric material may be selected to form an element having desired electrical characteristics. Alternatively, a material capable of adjusting optical characteristics may be selected to form an element having desired optical characteristics. In this example, a semiconductor material is selected, and an element function portion that functions as a semiconductor element is formed in part. In this example, a silicon single crystal is used as the functional layer 20.

  And the functional layer 20 is arrange | positioned on the support substrate 10 by bonding the support substrate 10 and the functional layer 20 together. Examples of the method of bonding the support substrate 10 and the functional layer 20 include a method of activating and bonding the surfaces of the surfaces to be bonded, and a method of bonding using electrostatic force. Examples of the method for activating the surface include a method of activating by irradiating an ion beam in a vacuum and etching the surface. This joining is preferably performed at room temperature. For this bonding, a method that does not use an adhesive such as a resin is adopted, and bonding is performed by solid state bonding using atomic force or the like.

  In this bonding step, the support substrate 10 having the central portion 11 and the peripheral edge portion 12 and the functional layer 20 may be bonded, or the flat support base and the functional layer 20 to be the support substrate 10 are bonded. After bonding, the support base is processed into the support substrate 10 having the central portion 11 and the peripheral portion 12 by reducing the thickness at the periphery of the main surface (upper surface) bonded to the functional layer 20. Also good.

  In this manner, by bonding the support substrate 10 and the functional layer 20 together, it is possible to suppress the presence of impurities between the support substrate 10 and the functional layer 20, and to obtain a high-quality composite substrate 1. . Further, since the support substrate 10 made of sapphire having high thermal conductivity is directly bonded to the functional layer 20, the composite substrate 1 having high heat dissipation can be obtained. Furthermore, since a silicon single crystal having high crystallinity can be used as the functional layer 20, the quality of the functional layer 20 can be improved as compared with the case where a functional layer having a different lattice constant is epitaxially grown on the support substrate 10.

  As a method of forming the peripheral edge portion 12 on the support base, for example, a method of partially removing using a photomask, a method of etching a desired portion using a mask, or a method of mechanically removing. Can be mentioned. Etching includes a chemical method and a physical method such as an ion beam. Examples of the mask include a metal mask and a photomask, which are appropriately selected according to the etching method.

  Here, the angle α can be adjusted to a desired angle when the peripheral edge portion 12 is formed. For example, when the support substrate 10 is formed by forming the peripheral portion 12 by etching from the bonding surface side of the support base with the functional layer 20, a desired angle is used by using a so-called resist (photomask) receding method. α may be formed. In this method, the end of the photomask is etched particularly quickly, so that it is possible to form a tapered shape using the mask receding phenomenon. In this case, it can be adjusted to a desired angle by appropriately setting the etching conditions. In addition, the taper angle formed on the side surface of the central portion 11 of the support substrate 10 can also be controlled by making the photomask itself tapered in advance and adjusting the taper angle of the photomask appropriately.

  Also, when forming the support substrate 10 by mechanically removing a part of the support base from the side of the bonding surface with the functional layer 20 to form the peripheral portion 12, the angle at which the grinding wheel is processed should be adjusted. Thus, the angle of the angle taper (angle α) can be adjusted.

  In this way, the composite substrate 1 in which the functional layer 20 covers the upper surface 11a of the central portion 11 of the support substrate 10 can be manufactured.

  In the composite substrate 1 described above, the peripheral portion 12 is made thinner than the central portion 11 in which the functional layer 20 on which the element functional portion that functions as a semiconductor element is formed. With such a configuration, even when an impact is applied to the composite substrate 1 from the outside, the peripheral edge portion 12 can alleviate the impact, and the stress due to the impact can be suppressed from being applied to the functional layer 20. It can be made highly. In other words, it is assumed that the peripheral portion 12 is damaged by an external impact, for example, by providing the peripheral portion 12 where the functional layer 20 having a lower strength than the central portion 11 where the functional layer 20 is disposed. In addition, the functional layer 20 on which the semiconductor element is formed can be protected from damage due to external impact.

  The upper surface 11a of the central portion 11 of the support substrate 10 and the functional layer 20 are directly bonded. In this case, since the buffer layer does not exist between the support substrate 10 and the functional layer 20, it is necessary to protect not only the functional layer 20 but also the support substrate 10 from stress caused by an external impact. For this reason, the peripheral edge 12 is important.

  Furthermore, the angle α formed between the side surface of the central portion 11 and the upper surface 12a of the peripheral edge portion 12 is an acute angle.

  For this reason, when a resist is applied to the functional layer 20 by spin coating in order to form a functional element in the functional layer 20, the surface tension at the peripheral portion 12 is reduced, and the wettability of the resist is improved. An increase in resist thickness at the outer edge can be suppressed. That is, a resist having a uniform thickness can be held. As a result, a functional element can be accurately formed in the functional layer 20.

  Further, when the resist is formed and heated by baking or the like, particularly strong stress is applied to the end portion of the resist, but the side surface of the central portion 11 of the support substrate 10 having higher strength than the functional layer 20 is applied. By relaxing the stress stepwise, it is possible to prevent unintended thermal stress from being applied to the functional layer 20.

  Furthermore, residues, particles, and the like can be guided to the outside of the functional layer 20 on the side surface of the central portion 11 of the support substrate 10 in resist peeling, functional layer 20 cleaning, and the like.

  In this example, the support substrate 10 is made of sapphire, which is a hydrophilic material, and the functional layer 20 is made of silicon, which is a water repellent material. According to such a configuration, for example, when the functional layer 20 is washed with pure water or an aqueous solution, or when the aqueous solution is brought into contact with the functional layer 20 for the purpose of etching or the like, the pure water or the aqueous solution is held at the peripheral portion 12. Then, the semiconductor layer 20 can be stably contacted.

<Modification of First Embodiment of Composite Substrate>
A modification of the composite substrate 1 that is an example of the embodiment of the composite substrate of the present invention will be described.

  In the composite substrate 1 shown in FIG. 1, it is preferable that the arithmetic average roughness of the upper surface 12 a of the peripheral portion 12 is larger than the arithmetic average roughness of the upper surface 11 a of the central portion 11. The upper surface 11a of the central portion 11 refers to a region covered with the functional layer 20.

By adopting such a configuration, stress due to external impact can be relaxed on the upper surface 12 a of the peripheral edge portion 12. That is, by using the upper surface 12a of the peripheral portion 12 as a fracture starting point, it is possible to suppress stress due to external impacts from being concentrated on the upper surface 11a of the central portion 11 covered by the functional layer 20, and Can be protected from external impact.

<Second Embodiment of Composite Substrate>
A composite substrate 1A which is an example of an embodiment of a composite substrate of the present invention will be described with reference to FIG. The composite substrate 1A includes a support substrate 10A having a central portion 11A and a peripheral portion 12A and a functional layer 20A. The composite substrate 1A differs from the composite substrate 1 in the shape of the functional layer 20A. Hereinafter, only different points will be described, and redundant description will be omitted.

  The functional layer 20A is located inside the outer edge of the central portion 11A in a top view. In other words, the upper surface 11Aa of the central portion 11A of the support substrate 10A has a covering region 11x where the functional layer 20A is located and an exposed region 11y exposed from the functional layer 20A. In other words, the side surface of the central portion 11A and the side surface of the functional layer 20A are shifted from each other in the cross-sectional view in the thickness direction.

  In this way, by arranging the exposed region 11y around the covering region 11x in a plan view, the side surface of the central portion 11A and the side surface of the functional layer 20A can be shifted and disposed, so that the central portion 11A due to external stress can be provided. The peeling between the covering region 11x and the functional layer 20A can be suppressed.

  Such an exposed region 11y may be formed by, for example, removing the outer peripheral portion of the functional layer 20A after disposing the functional layer 20A on the support substrate 10A, or having a smaller functional layer 20A than the central portion 11A in advance. May be prepared and arranged near the center on the central portion 11A.

  Note that the peripheral region (outer peripheral portion) of the functional layer 20A may be damaged in various processes for forming the composite substrate 1A. Therefore, if the exposed region 11y is formed by removing the outer peripheral portion of the functional layer 20A, the damaged region can be removed, and the quality of the functional layer 20A is improved.

  Further, when stress is applied from the outside, the stress is concentrated on the tapered portion formed by the side surface of the central portion 11A and the upper surface 12Aa of the peripheral edge portion 12A. Therefore, the functional layer 20 is disposed away from the tapered portion. It can suppress that layer 20A peels from the support substrate 10. FIG. In particular, since the exposed region 11y is provided in the present embodiment, the functional layer 20A can be isolated from the tapered portion. With such a configuration, peeling of the functional layer 20A can be further suppressed, and reliability can be improved.

<Modified example of composite substrate 1A>
Next, a modified example of the composite substrate 1A will be described.

  In the composite substrate 1A shown in FIG. 2, it is preferable that the arithmetic average roughness of the upper surface 12Aa of the peripheral portion 12A is larger than the arithmetic average roughness of the exposed region 11y of the central portion 11A.

  With such a configuration, it is possible to relieve stress due to external impact on the upper surface 12Aa of the peripheral edge portion 12A. That is, by using the upper surface 12Aa of the peripheral edge portion 12A as a fracture starting point, it is possible to suppress stress due to external impacts from being concentrated on the covering region 11x of the central portion 11A covered by the functional layer 20A. Can be protected from external impact.

In order to change the arithmetic average roughness between the exposed region 11y of the central portion 11A and the upper surface 12Aa of the peripheral portion 12A in this way, for example, sputtering or blasting is performed on the upper surface 12Aa of the peripheral portion 12A. What is necessary is just to add mechanical processing. At that time, a mask or the like may be disposed in the exposed region 11y to protect it. Further, when the peripheral portion 12A is formed by processing the support base, the surface (upper surface) 12a may be roughened simultaneously with the formation of the peripheral portion 12 by appropriately adjusting conditions such as etching. .

<Modified example of composite substrate 1, 1A>
Next, a composite substrate 1B, which is a modification of the composite substrates 1 and 1A, will be described with reference to FIG. Here, the configuration of the composite substrate 1A will be described as an example.

  The composite substrate 1B includes a support substrate 10B having a central portion 11B and a peripheral portion 12B, and a functional layer 20B. The upper surface 11Ba of the central portion 11B of the support substrate 10B has a covering region 11Bx where the functional layer 20B is located and an exposed region 11By exposed from the functional layer 20B. The side surface of the functional layer 20B is an inclined surface. Here, an angle formed between the side surface of the functional layer 20B and the upper surface 11Ba of the central portion 11B is defined as an angle β.

  In addition, the line connecting the upper end portion 20Bx and the lower end portion 20By of the functional layer 20B in a cross-sectional view in the thickness direction is not limited to a straight line, and may be a curve that is convex upward or downward. Moreover, the line which has a refractive part may be sufficient.

  In general, the angle β is a straight line connecting the upper end portion 20Bx and the lower end portion 20By when viewed in cross section, and an angle formed by the straight line and the upper surface 11Ba of the central portion 11 is obtained. However, this is not the case when the line connecting the upper end 20Bx and the lower end 20By is a curve or a line having a refracting part. In the case of a curved line, an angle formed between a tangent line in the vicinity of the lower end 20By of the curved line and the upper surface 11Ba of the central part 11 is defined as an angle β. In the case of a line having a refracting portion, an angle formed by a line connecting the refracting portion closest to the lower end portion 20By and the lower end portion 20By and the upper surface 11Ba of the central portion 11 is an angle β.

  Here, the angle β may be an acute angle. In that case, it can suppress that the resist thickness becomes thick in the peripheral part of the functional layer 20B. This is because, when a resist is applied by spin coating or the like in the photo process, the surface tension at the exposed region 11By and the peripheral portion 12 is reduced, and the wettability of the resist is improved. Accordingly, it is possible to provide a composite substrate 1B that can be easily processed accurately and has excellent productivity. In addition, the upper surface peripheral portion (upper end portion 20Bx) of the functional layer 20B is less likely to come into contact with other objects, and even if it comes into contact, the obtuse angle makes it difficult to cause chipping.

  Further, when the angle β is an acute angle and larger than the angle α, the function layer 20B is smoothly connected to follow the side surface from the outer edge (upper end portion 20Bx) to the support substrate 10B so as to draw an arc. Residues, particles, and the like can be guided from the layer 20B to the outside of the composite substrate 1B.

  On the other hand, when the angle β is an acute angle and smaller than the angle α, the adhesion strength of the end with respect to the support substrate 10B is reduced by loosening the taper of the functional layer 20B having a thickness smaller than that of the support substrate 10B. And the peeling of the functional layer 20B can be suppressed. In addition, by increasing the angle stepwise from the functional layer 20B toward the support substrate 10B, the wettability of the resist and the cleaning liquid is improved, and the retention of the resist with a uniform thickness and the generation of particles due to the residue of the cleaning liquid are suppressed. It will be possible. Such an angle β may be, for example, 5 ° to 40 °.

Since the edge of the functional layer 20B having such an angle β is located on the inner side of the end portion 11Be of the central portion 11B in top view, when stress is applied from the outside, the stress is concentrated on the tapered portion. Therefore, the functional layer 20B can be prevented from peeling from the support substrate 10 by disposing the functional layer 20B away from the tapered portion.

  Furthermore, the arithmetic average roughness Ra of the side surface of the functional layer 20B is preferably larger than the arithmetic average roughness Ra of the exposed region 11By of the support substrate 10B and smaller than the arithmetic average roughness Ra of the upper surface of the peripheral edge portion 12B. .

  By making the arithmetic average roughness Ra of the side surface of the functional layer 20B larger than the Ra of the exposed region 11By, when the resist is applied to the functional layer 20B, the resist is surely held by an anchor effect at an end portion that is easily peeled off. Therefore, accurate machining can be easily performed. Further, by making the arithmetic mean roughness Ra of the side surface of the functional layer 20B smaller than Ra on the upper surface of the peripheral edge portion 12B, the cleaning liquid collected on the side surface of the functional layer 20B can easily flow to the support substrate 10B side, The particles can be smoothly guided outside the functional layer 20B. Thereby, generation | occurrence | production of the particle by the residue of a washing | cleaning liquid can be suppressed. In particular, when the support substrate 10B is made of hydrophilic sapphire and the functional layer 20B is made of hydrophobic silicon, in the processing and cleaning process of the functional layer 20B, a liquid such as cleaning water held by the support substrate 10B is used. The liquid can be brought into contact with the upper end portion of the layer 20B. This is because the arithmetic average roughness Ra of the side surface of the functional layer 20B is small, so that the contact area of the solution can be increased. Here, it is preferable to make the angle β smaller than the contact angle of water because the above-described solution can be easily brought into contact with the side surface of the functional layer 20B.

  Further, since the Ra on the side surface of the functional layer 20B is smaller than the Ra on the upper surface 12Ba of the peripheral edge portion 12B, the external stress is concentrated on the peripheral edge portion 12B, so that the damage to the functional layer 20B is small and the highly reliable composite. The substrate 1B can be manufactured.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

  For example, the composite substrates (1, 1A, 1B) shown in FIGS. 1 to 3 are arranged so that the peripheral portions (12, 12A, 12B) surround the central portions (11, 11A, 11B). 11 may be arranged in a part of the peripheral region.

  Similarly, the exposed region 11y is disposed so as to surround the covering region 11x, but may be disposed in a part of the peripheral region of the covering region 11x.

  Alternatively, the functional layer (20, 20A, 20B) may be formed by directly bonding a semiconductor substrate to the support substrate (10, 10A, 10B) and processing the semiconductor substrate to a desired thickness. Various methods such as abrasive polishing, chemical etching, and ion beam etching can be adopted as the thinning method, and a plurality of methods may be combined.

When processing thinly, you may employ | adopt simultaneously the process which makes the surface of a semiconductor substrate flat by precision etching. Examples of the etching means used for this precise etching include dry etching. This dry etching includes a chemical reaction and a physical collision. Examples of utilizing chemical reactions include reactive gases (gas), ions and ion beams, and those utilizing radicals. Examples of the etching gas used for the reactive ions include sulfur hexafluoride (SF ₆ ) and carbon tetrafluoride (CF ₄ ). Moreover, what uses an ion beam is mentioned as a thing by physical collision. One using this ion beam includes a method using a gas cluster ion beam (GCIB). By scanning a semiconductor substrate with a movable stage while etching a narrow region using these etching means, accurate etching can be performed satisfactorily even for a large-area material substrate. Further, wet etching, mechanical polishing, or mechanochemical polishing may be performed.

  Here, using a semiconductor substrate having a dopant concentration distribution at least in a certain region to be bonded to the support substrate, the semiconductor substrate is thinned by mechanical grinding, and then isotropic mirror etching is performed. Thereafter, it is preferable to obtain a functional layer (20, 20A, 20B) having a desired thickness by etching having selectivity with respect to the dopant concentration. The following steps can be exemplified as examples using selective etching. That is, first, as a semiconductor substrate, a region (hereinafter referred to as a first region) in which the dopant concentration increases from the side bonded to the support substrate to the opposite main surface is formed in advance. Then, when the first substrate is thinned to be a functional layer after bonding to the support substrate, an etchant for selective etching whose etching rate is remarkably reduced when the dopant concentration falls below a certain threshold may be used. As such an etchant, for example, when a Si substrate is used as a semiconductor substrate and boron (B) is used as a dopant, a mixed solution of hydrofluoric acid, nitric acid, and acetic acid can be exemplified. By using the semiconductor substrate and the etchant, the etching rate by selective etching is reduced in the middle of the thickness of the semiconductor substrate (in the middle of the thickness of the first region), and a part of the first region is caused to function as an etching stop layer. be able to. By appropriately adjusting the thickness position of the first region and the dopant concentration distribution in the first region in the semiconductor substrate, it is possible to reduce the thickness to a desired thickness position.

  In the thinning process of the semiconductor substrate until reaching the first region, it is preferable to perform mechanical grinding and isotropic mirror etching. By thinning in this order, the time and cost for thinning can be reduced, productivity can be improved, and the upper surface of the functional layer can be made flat. In particular, by adopting the steps of mirror etching and selective etching in this order when forming the functional layer 20B, the side surface taper of the functional layer 20B is made acute and the arithmetic average roughness Ra is reduced. And Ra on the upper surface of the functional layer 20B can be reduced.

  In FIG. 4, the shape of the outer peripheral portion of the functional layer 20B when the mirror surface etching and the selective etching are performed in this order and when only the selective etching is performed is measured by a stylus type surface shape measuring device (Deck tack). Results are shown. As is clear from FIG. 4, mirror etching and selective etching are performed in this order, so that the angle β can be made acute without using a mask or the like, and the arithmetic of the side surface of the functional layer 20B is performed. It was confirmed that the average roughness Ra can be reduced.

  In the case of only selective etching, it is expected that the concentration of the etching solution and the flow of the etching solution are not uniform near the outer periphery of the functional layer 20B, and as a result, it is difficult to control the etching rate near the outer periphery. Specifically, the etching rate at the outer periphery tends to decrease. On the other hand, it is confirmed that the functional layer 20B having a desired shape can be provided even after subsequent selective etching by positively proceeding with the etching of the outer peripheral portion of the functional layer 20B by mirror etching in advance. did it.

1, 1A, 1B ... Composite substrate 10, 10A, 10B ... Support substrate 10a ... Upper surface 11, 11A, 11B ... Central portion 11x ... Exposed region 11y ... Covered region 12, 12A , 12B ... peripheral edge 20, 20A, 20B ... functional layer

Claims (4)

The peripheral portion has a central portion and a peripheral portion, and in the side view, the peripheral portion is located on the lower side of the upper surface of the central portion, the thickness thereof is thinner than the central portion, A support substrate in which an angle α formed between the upper surface of the peripheral portion and the side surface of the central portion is an acute angle;
See containing and a functional layer disposed on the central portion of the supporting substrate,
The functional layer is located inside the outer edge of the upper surface of the central portion of the support substrate in a top view,
The arithmetic average roughness of the side surface of the functional layer is larger than the arithmetic average roughness of the region exposed from the functional layer in the upper surface of the central portion of the support substrate, and is larger than the arithmetic average roughness of the upper surface of the peripheral portion. Smaller than
Double if the substrate. The composite substrate according to claim 1, wherein the support substrate is sapphire and the functional layer is made of silicon .   The composite substrate according to claim 1, wherein an angle β formed between a side surface of the functional layer and an upper surface of the central portion of the support substrate is smaller than the angle α. The composite substrate according to claim 1 , wherein the functional layer is made of a piezoelectric material .

Images