JP2015144228A - semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an effective technique for relaxing a thermal stress generated at a bonding layer with a simple structure in a semiconductor device in which a semiconductor element is bonded on a substrate through the bonding layer.SOLUTION: A semiconductor device 100 includes: a metal substrate 110; and a semiconductor element 120 bonded to the substrate 110 through a bonding layer 130 composed only of a bonding material coated to a bonding region 112 on the substrate 110. A shape of an outer periphery part of the bonding layer 130 is constituted of an R part 131 having a predetermined radius of curvature.

Description

  The present invention relates to a semiconductor device in which a semiconductor element is bonded to a substrate via a bonding layer.

  In recent years, in this type of semiconductor device, the operating temperature level of the semiconductor has increased, and there is a demand for device design that takes heat resistance into consideration. Specifically, since a high thermal stress at the bonding interface between the substrate and the semiconductor element may cause peeling or cracking at the bonding interface, various techniques for relaxing the thermal stress to solve this problem Development is in progress.

  Conventionally, as an example of a technique focusing on thermal stress relaxation at a bonding interface between a substrate and a semiconductor element, for example, semiconductor devices disclosed in Patent Documents 1 to 3 below are known. The semiconductor devices disclosed in Patent Documents 1 and 2 are configured such that a semiconductor element is bonded to a substrate in a state where a stress relaxation member or an intermediate material is sandwiched between bonding material layers where thermal stress is concentrated. The semiconductor device disclosed in Patent Document 3 is configured such that a thermoplastic bonding layer is interposed between a substrate and a semiconductor element, and a part of the thermoplastic bonding layer is liquid-layered (softened) by temperature control. ing.

JP 2008-277317 A JP 2012-291302 A JP 2013-84657 A

(Problems to be solved by the invention)
Since the semiconductor device disclosed in Patent Documents 1 and 2 has a structure in which a stress relaxation member or an intermediate material, which is a member different from the substrate and the semiconductor element, is interposed at the bonding interface between the substrate and the semiconductor element. In addition, the manufacturing process is complicated and the manufacturing cost is increased. In these semiconductor devices, since the bonding material layers are multi-layered, the bonding strength may be reduced due to the occurrence of defects when the bonding state between the layers is not good. Since the semiconductor device disclosed in Patent Document 3 requires a large-scale system including a temperature sensor and a control mechanism for controlling the temperature of the thermoplastic bonding layer, the structure is complicated and the manufacturing cost increases. I have it. Further, in this semiconductor device, since a plurality of bonding materials are interposed in the bonding material layer, the bonding strength is reduced due to the generation of voids and gaps due to the difference in physical property values (melting point, linear expansion coefficient) between the bonding materials. There is a fear.

  The present invention has been made in view of the above points, and one of its purposes is to simplify thermal stress generated in a bonding layer in a semiconductor device in which a semiconductor element is bonded to a substrate via a bonding layer. It is to provide an effective technique to alleviate the structure.

(Means for solving the problem)
In order to achieve the above object, a semiconductor device according to the present invention includes a substrate and a semiconductor element (also referred to as “semiconductor chip”) bonded to the substrate through a bonding layer made of only a bonding material. A bonding layer is formed by heating with a bonding material interposed between the substrate and the semiconductor element. In this case, a member different from the substrate and the semiconductor element is not interposed in the bonding layer that is a bonding interface between the substrate and the semiconductor element. Therefore, the structure of the bonding layer itself is simplified. Further, the shape of the outer peripheral portion of the bonding layer is constituted by an R portion having a predetermined radius of curvature (R dimension). In this case, the stress concentration is less likely to occur in the R portion of the bonding layer than the sharply protruding corner portion, and the thermal stress generated at the bonding interface can be relaxed with a simple structure. In addition, since only the shape of the outer peripheral portion of the bonding layer needs to be changed, the manufacturing process can be simplified and the manufacturing cost can be reduced. In the present invention, it is preferable to exclude all corners of the outer peripheral portion of the bonding layer. However, if at least one R portion is provided in the outer peripheral portion of the bonding layer, a thermal stress relaxation effect can be obtained. .

  In the semiconductor device having the above-described configuration, it is preferable that the bonding layer has a cylindrical shape, and the circular arc radius of the cylindrical shape corresponds to a predetermined curvature radius of the R portion. In this case, the entire outer peripheral portion of the bonding layer is configured as one R portion. As a result, the radius of curvature of the R portion is increased, which is effective in enhancing the effect of mitigating thermal stress.

  In the semiconductor device having the above structure, it is preferable that the bonding layer is formed by heating after a bonding material having thermal fluidity is applied to the bonding region. In this case, the semiconductor device preferably further includes a shape maintaining mechanism for maintaining the shape of the bonding material before and after heating. As a result, it is possible to reliably realize a desired shape of the bonding layer that is effective in enhancing the effect of mitigating thermal stress.

  In the semiconductor device having the above configuration, the shape maintaining mechanism is preferably formed of a concavo-convex structure on the order of nanometers formed on the substrate so as to partition around the bonding region and having a liquid repellent effect on the bonding material. In this case, the bonding material applied to the bonding region hardly flows out of the bonding region beyond the concavo-convex structure on the nanometer order even when it exhibits thermal fluidity by heating. This makes it possible to maintain the shape of the bonding material before and after heating using a physical structure.

  In the semiconductor device having the above structure, the concavo-convex structure is preferably formed by laser processing that irradiates a femtosecond laser on the substrate. Thereby, the uneven structure of nanometer order can be reliably formed using a femtosecond laser.

  In the semiconductor device having the above configuration, the semiconductor element is bonded to the substrate via the auxiliary bonding layer made of only the bonding material in addition to the bonding layer, and the auxiliary bonding layer is located near the R portion in the outer peripheral portion of the bonding layer. Preferably it is arranged. In this case, the auxiliary bonding layer can compensate for the decrease in the bonding area by providing the R portion on the outer peripheral portion of the bonding layer. As a result, it is possible to suppress a decrease in electrical conductivity and heat dissipation between the substrate and the semiconductor element.

  The semiconductor device having the above structure preferably includes a concavo-convex structure in a bonding region on the substrate. Thereby, the bonding area of the substrate with respect to the bonding layer can be increased, and the bonding strength between the substrate and the bonding layer can be increased.

  The semiconductor device having the above structure preferably includes a groove extending in a long shape in a bonding region on the substrate and having a corrugated cross section having a micrometer order, and the groove constitutes an uneven structure. Thereby, in the case of the base structure which is a flat surface (smooth surface), the shear stress which generate | occur | produces linearly along a flat surface can be disperse | distributed in a some direction with the groove | channel with a wavy cross section. As a result, the thermal stress generated at the bonding interface between the substrate and the bonding layer is relaxed and the thermal fatigue life is improved.

  In the semiconductor device having the above structure, the groove preferably extends continuously from the bonding region to the non-bonding region where the bonding material is not applied on the substrate. Thereby, the organic solvent contained in the bonding material can be discharged from the bonding region to the non-bonding region through the groove. As a result, it is possible to suppress the generation ratio of voids generated due to the residual organic solvent.

  In the semiconductor device having the above configuration, it is preferable that a plurality of grooves extend radially from the central portion of the bonding region to the non-bonding region. In this case, since the organic solvent generally remains in the vicinity of the center of the joining region and voids are easily formed, the use of radial grooves as a means for discharging the organic solvent has a more effective effect of reducing the void generation rate. Get higher.

  The semiconductor device having the above structure is preferably formed by laser processing that irradiates a femtosecond laser on a groove or a substrate. Thereby, the groove | channel where a cross section is a wave shape of a micrometer order can be reliably formed using a femtosecond laser.

  The semiconductor device having the above-described structure preferably further includes a connection groove for connecting adjacent grooves in a bonding region on the substrate. According to this connection groove, in the structure in which the organic solvent contained in the metal nanopaste as the bonding material is guided from the bonding region to the non-bonding region using a plurality of grooves, the direction in which the organic solvent can be guided is set. Can be increased. As a result, even when the organic solvent stagnates or remains in an arbitrary groove, the organic solvent can be reliably guided to the non-joining region through the another groove after being guided to the other groove through the connection groove.

  In the semiconductor device having the above configuration, it is preferable that the cross section of the connection groove is wavy. As a result, the thermal stress (thermal strain) accumulated in the bonding layer under a severe temperature environment can be applied to a plurality of directions (for example, a normal vector direction at an arbitrary point of the wave) by the connecting groove having a wavy cross section. Can be dispersed. As a result, even if the cooling cycle is repeated a plurality of times, it is possible to suppress or delay the progress of cracks in the bonding layer.

  In the semiconductor device having the above configuration, it is preferable that a plurality of connection grooves are arranged so as to extend concentrically around the center portion of the bonding region. Thereby, when a thermal stress (thermal strain) acts in the circumferential direction of the bonding layer, the thermal stress can be reliably dispersed in a plurality of directions by the connection grooves.

  In the semiconductor device having the above structure, it is preferable that the connection groove continues from the bonding region to the non-bonding region where the bonding material is not applied on the substrate. In this case, in addition to the first function of connecting the plurality of grooves, the connection groove has a second function of guiding the organic solvent contained in the metal nanopaste as the bonding material from the bonding region to the non-bonding region. Can fulfill. In particular, when both the groove and the connection groove extend continuously from the bonding region to the non-bonding region, the organic solvent contained in the metal nano paste is not bonded by the cooperation of these two types of grooves. The function of guiding to the area can be strengthened.

  As described above, according to the present invention, in a semiconductor device in which a semiconductor element is bonded to a substrate via a bonding layer, it is possible to reduce thermal stress generated in the bonding layer with a simple structure.

FIG. 1 is a perspective view showing a schematic configuration of a semiconductor device 100 according to an embodiment of the present invention. FIG. 2 is a plan view of the semiconductor device 100 in FIG. FIG. 3 is a diagram schematically showing thermal stress St generated by thermal change in the bonding layer 130 in FIG. 4 is a plan view of a bonding layer 230 according to a modified example of the bonding layer 130 in FIG. FIG. 5 is a graph showing the relationship (CAE analysis) between the R dimension of the bonding layer and the maximum stress. FIG. 6 is a graph showing the maximum stress (CAE analysis) for each of the base-shaped bonding layer, the bonding layer whose four corners are R1.2, and the circular bonding layer. FIG. 7 is a plan view of a bonding layer 330 according to a modified example of the bonding layers 130 and 230. FIG. 8 is a plan view of a bonding layer 430 according to a modified example of the bonding layers 130 and 230. FIG. 9 is a plan view of a semiconductor device 200 according to a modification of the semiconductor device 100 in FIG. FIG. 10 is a diagram showing a cross-sectional structure taken along the line AA of the semiconductor device 200 in FIG. FIG. 11 is an enlarged cross-sectional view of the liquid repellent portion 141 in FIG. FIG. 12 is a plan view of the concavo-convex structure 150 provided on the substrate 110 in the semiconductor device 300 of the present invention. FIG. 13 is a diagram showing the undulation shape of the cross section of the groove 151 of the concavo-convex structure 150 in FIG. FIG. 14 is a graph showing the maximum stress (CAE analysis) for each of the base structure and the concavo-convex structure 150. FIG. 15 is a diagram schematically showing a state in which the bonding material in the groove 151 of the concavo-convex structure 150 is heated and when the bonding is completed. FIG. 16 is a diagram schematically showing a state of measurement of the tensile breaking strength of the joined body TP. FIG. 17 is a graph showing the bonding strength for each of the base structure and the concavo-convex structure 150. FIG. 18 is a diagram schematically showing an internal inspection of the bonding layer 130 by X-ray and optical microscope (SEM) related to void evaluation. FIG. 19 is a graph showing the void ratio for each of the base structure and the concavo-convex structure 150. FIG. 20 is a plan view of a concavo-convex structure 250 according to a modified example of the concavo-convex structure 150. FIG. 21 is a plan view of a concavo-convex structure 350 according to a modified example of the concavo-convex structure 150. FIG. 22 is a plan view of a concavo-convex structure 450 according to a modified example of the concavo-convex structure 150. FIG. 23 is a plan view of a concavo-convex structure 550 according to a modified example of the concavo-convex structure 150. FIG. 24 is a plan view of a concavo-convex structure 650 according to a modified example of the concavo-convex structure 150. FIG. 25 is a view showing the undulation shape of the cross section of the connection groove 253 of the concavo-convex structure 650 in FIG. FIG. 26 is a diagram illustrating an example of a void V that can be generated in the bonding layer 130 by a cooling / heating cycle. FIG. 27 is a partially enlarged view of the concavo-convex structure 650 in FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, a semiconductor device 100 as a “semiconductor device” of the present invention is bonded to a substrate (semiconductor substrate) 110 and a substrate 110 (an upper surface 111 of the substrate 110) via a bonding layer 130. A semiconductor element (semiconductor chip) 120. The substrate 110, the semiconductor element 120, and the bonding layer 130 here correspond to the “substrate”, “semiconductor element”, and “bonding layer” of the present invention, respectively.

  The substrate 110 is configured as a plate-like member having a square shape or a rectangular shape as shown in FIG. 2 and having a predetermined plate thickness. The substrate 110 is typically made of metal made of copper or a copper alloy, and the upper surface 111 of the substrate 110 is plated with nickel.

  The semiconductor element 120 is typically configured as a plate-like member that has a square shape in plan view as shown in FIG. 2 and has a predetermined plate thickness. The semiconductor element 120 is configured as a semiconductor element made of SiC (silicon carbide). A wiring joint portion (not shown) is formed on the surface of the semiconductor element 120 (the surface opposite to the surface facing the upper surface 111 of the substrate 110), and electrical wiring is connected to the wiring joint portion. .

  The bonding layer 130 is interposed between a bonding region (upper surface) 112 that is a surface facing the semiconductor element 120 on the upper surface 111 of the substrate 110 and 112 at the bottom surface of the semiconductor element 120. The bonding layer 130 has a circular shape as viewed in plan as shown in FIG. 2 and a cylindrical shape having a predetermined film thickness. The bonding layer 130 is made of a metal nano paste containing an organic solution (organic solvent) and metal nanoparticles having a particle diameter of several nanometers to several tens of nanometers (metal nanoparticles containing silver, copper, nickel, etc.), or by heating. It consists only of a joining material such as solder, which is an alloy mainly composed of lead and tin that has fluidity and fluidity. In this case, a member different from the substrate 110 and the semiconductor element 120 is not interposed in the bonding layer 130 that is a bonding interface between the substrate 110 and the semiconductor element 120. Therefore, the structure of the bonding layer 130 itself is simplified.

  In order to form the bonding layer 130, for example, a metal nano paste as a bonding material is applied or transferred to the bonding region 112 on the substrate 110, and then the bottom surface 121 of the semiconductor element 120 is covered with the metal nano paste. And heat treatment in a non-oxidizing atmosphere. According to this heat treatment, metal nanoparticles are deposited from the organic solution in the bonding material and deposited on the nickel plating, while the organic solution is volatilized and removed. Furthermore, heat treatment in an oxidizing atmosphere can be performed. According to this heat treatment, the organic protective film adsorbed on the surface of the metal nanoparticles is decomposed and removed by heating, and the sintering behavior of the metal nanoparticles is promoted. A metallic bonding action can be obtained between the two. Eventually, the bonding layer 130 is formed from the bonding material.

  By the way, when the temperature of the semiconductor element 120 rises when the semiconductor device 100 having the above configuration is used, a thermal change is applied to the bonding layer 130 that forms the bonding interface between the substrate 110 and the semiconductor element 120. In this case, a thermal stress that is an internal force is generated by a thermal change of the bonding layer 130. Therefore, in this type of semiconductor device 100, a structure for preventing peeling and cracks from occurring due to the thermal stress concentration at which the thermal stress is locally concentrated in the bonding layer 130 is required.

  Therefore, in this embodiment, the cylindrical bonding layer 130 is employed. The bonding layer 130 has a circular shape in plan view, that is, an outer peripheral portion thereof is configured by an R portion 131 having a constant curvature radius (arc radius). That is, the entire outer peripheral portion of the bonding layer 130 is configured as one R portion 131. This shape does not have a “corner (a sharply protruding portion)” with respect to a general shape of the bonding layer (for example, a shape such as a square, a rectangle, or a polygon in plan view). Is different. The bonding layer 130 of this shape can relieve the thermal stress by removing the corner portion where the thermal stress tends to concentrate from the outer peripheral portion. Thereby, the thermal stress which arises in a joining interface with a simple structure can be relieved. In particular, when the bonding layer 130 has a cylindrical shape, the thermal stress St generated by the thermal change in the bonding layer 130 can be evenly distributed in the outer peripheral direction, for example, as indicated by the arrow in FIG. On the other hand, for example, in the case of a bonding layer having a square shape in plan view (hereinafter also referred to as “base shape”), thermal stress exceeding the yield stress of the bonding layer is likely to concentrate on the corners, and as a result, peeling occurs. Or cracks may occur. Further, according to the present embodiment, it is only necessary to change the shape of the outer peripheral portion of the bonding layer, so that the manufacturing process can be simplified and the manufacturing cost can be reduced. Furthermore, a particularly reliable semiconductor device can be constructed in a system that requires a thermal stress relaxation effect such as a high-temperature cooling / heating cycle.

  As a modified example of the bonding layer 130 having the above-described configuration, bonding layers having various shapes that are effective in eliminating corners from the outer peripheral portion and preventing a substantial bonding area involved in bonding from being reduced are employed. be able to. For example, the shape of the bonding layer in plan view may be an ellipse. Further, a bonding layer 230 having a shape as shown in FIG. 4 may be employed. The bonding layer 230 is formed by applying R to each of the four corners of the bonding layer that is square in plan view. That is, the shape of the outer peripheral portion of the bonding layer 230 is constituted by four R portions 231 having a predetermined radius of curvature. According to the bonding layer 230, thermal stress can be relieved in the same manner as the cylindrical bonding layer 130, and the bonding layer 130 is used for a semiconductor element having the same dimensions as the semiconductor element 120 allocated to the bonding layer 130. It becomes possible to increase the bonding area. By increasing the bonding area, it is possible to ensure the bonding strength with respect to each of the substrate 110 and the semiconductor element 120, and to suppress the decrease in electrical conductivity and heat dissipation between the substrate 110 and the semiconductor element 120. Can do.

  The effects of the bonding layers 130 and 230 having the above-described configuration can be confirmed by a simulation based on a known CAE (Computer Aided Engineering) analysis. In this case, the bonding layer to be analyzed can be modeled, and the thermal stress generated in the bonding layer can be calculated using an appropriate numerical analysis method. As a specific example, a heat amount application process in which a heat amount is applied so that the central portion of the semiconductor element 120 (a chip having a vertical dimension and a horizontal dimension of 5 mm) is approximately 250 [° C.] is assumed. The thermal stress generated in the above is derived by CAE analysis when the R dimension (also referred to as “curvature radius”) of the outer peripheral portion of the bonding layer is variously changed. As a result, analysis results as shown in FIGS. 5 and 6 were obtained. According to FIG. 5, as the shape of the bonding layer in plan view approaches the circular shape (perfect circle) from the base shape, the maximum value of thermal stress generated in the bonding layer (hereinafter also referred to as “maximum stress”) decreases. It was confirmed that the maximum value of thermal stress was the lowest when it was circular. This maximum stress decreases relatively remarkably, particularly until the R dimension reaches R1.2, and gradually decreases until it reaches 1.2 after exceeding 1.2. Further, as shown in FIG. 6, the maximum stresses for the base-shaped bonding layer, the bonding layer having four corners of R1.2, and the circular bonding layer are 144 [MPa] and 101 [MPa], respectively. 84.8 [MPa]. Based on these analysis results, it was confirmed that the effect of alleviating thermal stress was particularly enhanced by determining the shape of the outer peripheral portion of the bonding layer so that the R dimension exceeded 1.2.

  Moreover, it can replace with the joining layers 130 and 230 of the said structure, and can also employ | adopt the joining layer of another shape shown in FIG.7 and FIG.8. The bonding layer 330 illustrated in FIG. 7 includes a main bonding layer 331 having the same shape as the bonding layer 130 and four auxiliary bonding layers 332 disposed around the main bonding layer 331 in addition to the main bonding layer 331. In this case, the semiconductor element 120 is bonded to the substrate 110 via one main bonding layer 331 and four auxiliary bonding layers 332. Further, the bonding layer 430 shown in FIG. 8 includes a circular main bonding layer 431 having a smaller diameter than the bonding layer 130 and eight auxiliary bonding layers 432 arranged around the main bonding layer 431 at equal intervals. And. In this case, the semiconductor element 120 is bonded to the substrate 110 via one main bonding layer 431 and eight auxiliary bonding layers 432. Each of these auxiliary bonding layers 332 and 432 is a bonding layer made of only the same bonding material as the bonding layer 130, and the bonding area is larger than that of the base-shaped bonding layer by providing an R portion on the outer peripheral portion of the bonding layer 130. Fulfills the function of compensating for the decline. For this purpose, each auxiliary bonding layer 332 is disposed in the vicinity of the R portion in the outer peripheral portion of the main bonding layer 331. Similarly, each auxiliary bonding layer 432 is disposed in the vicinity of the R portion in the outer peripheral portion of the main bonding layer 431. As a result, it is possible to suppress a decrease in electrical conductivity and heat dissipation between the substrate 110 and the semiconductor element 120. The auxiliary bonding layers 332 and 432 here correspond to the “auxiliary bonding layers” of the present invention.

  In order to realize the shape of the bonding layers 130, 230, 330, and 430 having the above configuration, a shape maintaining mechanism for maintaining the shape of the bonding material forming the bonding layer before and after heating is provided on the substrate 110. Is preferred. 9 and 10 are referred to for the semiconductor device 200 including the shape maintaining mechanism 140 which is an example of the shape maintaining mechanism. This semiconductor device 200 is different from the semiconductor device 100 shown in FIGS. 1 and 2 only in that the shape maintaining mechanism 140 is provided. The shape maintaining mechanism 140 here corresponds to the “shape maintaining mechanism” of the present invention.

  If the bonding material before the bonding layer 130 is formed flows out of the bonding region 112 on the substrate 110 due to thermal fluidity during heating, the bonding layer 130 having a desired shape may not be obtained. Therefore, the shape maintaining mechanism 140 according to the present embodiment functions to prevent the bonding material from flowing out of the bonding region due to thermal fluidity during heating. As shown in FIGS. 9 and 10, the shape maintaining mechanism 140 includes a liquid repellent portion 141 and a receiving groove 142 provided on the substrate 110.

  The liquid repellent portion 141 is configured using a plurality of concentric annular grooves formed on the substrate 110 so as to partition around the circular bonding region 112. The plurality of annular grooves can be formed by laser processing that irradiates the upper surface 111 of the substrate 110 with a known femtosecond laser, an optical laser that oscillates by compressing energy in a short time, generally in units of femtoseconds. In this case, for example, as shown in FIG. 11, in the cross section of the liquid repellent portion 141, the interval D1 between two adjacent convex portions is 700 to 800 [nm], and the height of the convex portion (depth of the concave portion). ) An uneven structure in which D2 is 800 to 1000 [nm] and the width D3 of the recess is 150 to 300 [nm] is included. Such a concavo-convex structure of nanometer order (nano-periodic structure) has poor wettability with respect to the bonding material and exhibits a liquid repellent action (so-called “lotus effect”) that repels the bonding material. A femtosecond laser is particularly effective for reliably forming a concavo-convex structure on the order of nanometers. For this reason, when the bonding material that is about to flow out radially outward from the circular bonding region 112 acts on the uneven portion of the liquid repellent portion 141, the bonding material is repelled by the liquid repellent action of the uneven portion, and the bonding material is It is possible to prevent the wetting and spreading beyond the liquid repellent portion 141. In this case, the bonding material can be prevented from flowing out of the bonding region 112 by a physical structure. As a result, since the shape of the bonding material before and after heating is maintained, the desired shape of the bonding layer effective for enhancing the effect of mitigating thermal stress can be reliably realized.

  The receiving groove 143 functions to store the excess bonding material when the bonding material is excessively applied to the bonding region 112 due to variations in the amount of bonding material applied. As a result, the bonding material can be physically suppressed from flowing out of the bonding region 112. The receiving groove 143 can be formed by using a well-known femtosecond laser used to form the liquid repellent portion 141 under irradiation conditions different from those for the liquid repellent portion 141. In the present embodiment, the shape maintaining mechanism 140 is constructed by combining the receiving groove 143 with the liquid repellent portion 141. However, in the present invention, the shape maintaining mechanism is configured using at least one of the liquid repellent portion 141 and the receiving groove 143. Can be built. For example, the receiving groove 143 can be omitted as necessary.

  A semiconductor device 300 shown in FIG. 12 is characterized by a surface structure on the substrate 110, while the semiconductor device 100 having the above-described structure is characterized by the shape of the outer peripheral portion of the bonding layer. More specifically, the semiconductor device 300 includes a concavo-convex structure 150 in the bonding region 112 on the substrate 110. The concavo-convex structure 150 includes a plurality of grooves 151 that are arranged in parallel to each other and each extend in a long shape. Specifically, as shown in FIG. 13, each groove 151 extends in a long shape in the bonding region 112 on the substrate 110. With respect to the groove cross section of the groove 151 (also simply referred to as “cross section”), the groove cross section (A′-A ′ line cross section in FIG. 12) in the direction intersecting the extending direction of the plurality of grooves 151 is micrometer. It is preferable to employ a concavo-convex structure (hereinafter also referred to as “first cross-sectional structure”) having an undulating shape (also referred to as “wave shape”). In the groove cross section, for example, the distance D4 between two adjacent convex portions is approximately 60 [μm] or less, and the height (depression depth) D5 of the convex portions is approximately 20 to 30 [μm], which is regular. A wavy shape in which the groove height changes with periodicity (a shape in which a wavy line passing through the groove top and bottom of the groove in the groove cross section continues periodically (sinusoidal waveform)) is included. In this case, all of the plurality of grooves 151 can be formed by laser processing that irradiates the upper surface 111 of the substrate 110 with a femtosecond laser. A femtosecond laser is particularly effective for reliably forming an uneven structure on the order of micrometers. In addition to or in addition to the first cross-sectional structure described above, the groove cross section (the cross section along line A ″ -A ″ in FIG. 12) in the extending direction of the plurality of grooves 151 has a wavy shape on the order of micrometers. A concavo-convex structure (hereinafter also referred to as “second cross-sectional structure”) that is (also referred to as “wavy”) may be employed.

  According to such a micrometer-order concavo-convex structure 150 (micro-periodic structure) formed on the substrate 110, the bonding region 112 has a flat surface (smooth surface) (hereinafter also referred to as “base structure”). In comparison, the bonding area of the substrate 110 to the bonding layer 130 can be increased, and the bonding strength between the substrate 110 and the bonding layer 130 can be increased. Further, in the case of the base structure, the shear stress generated linearly along the flat surface is changed into a plurality of directions (a plurality of directions intersecting the flat surface, for example, undulations (waves) at arbitrary points by the wavy shape of the groove 151. Normal vector direction). As a result, the thermal stress generated at the bonding interface between the substrate 110 and the bonding layer 130 is relaxed and the thermal fatigue life is improved. Note that the bonding layer 130 in the semiconductor device 300 may have a corner in the outer peripheral portion such that the shape in plan view is square or rectangular, or the outer peripheral portion as shown in FIGS. It may have a shape with no corners. The concavo-convex structure 150 and the groove 151 here correspond to the “concavo-convex structure” and “groove” of the present invention, respectively.

  The effect of thermal stress dispersion by the concavo-convex structure 150 can be confirmed by the simulation by the CAE analysis described above. In this case, assuming the same process as the heat application process described above, the thermal stress generated in the bonding layer during the heat application process was calculated by CAE analysis. As a result, an analysis result as shown in FIG. 14 was obtained. According to FIG. 14, the maximum stress generated in the bonding layer was 144 [MPa] in the case of the base structure, whereas it was 106.9 [MPa] in the case of the concavo-convex structure 150. Based on this analysis result, it was confirmed that by adopting the concavo-convex structure 150, the effect of relieving thermal stress is enhanced.

  Each groove 151 of the concavo-convex structure 150 is a region (bonding material) that does not participate in bonding to the bonding material on the substrate 110 from the bonding region 112 that is a region related to bonding to the bonding material (region to which the bonding material is applied). It is preferable to be configured so as to continuously extend to the non-bonding region 113 which is a region where no coating is applied. According to this configuration, each groove 151 can serve as a guide groove that guides the organic solvent contained in the metal nanopaste to the non-bonding region 113 when the metal nanopaste is used as the bonding material. In particular, in the case of the first cross-sectional structure described above, the position of the groove bottom of each groove 151 does not change from the bonding region 112 to the non-bonding region 113 in a substantially constant manner, so that the organic solvent is reliably transferred from the bonding region 112 to the non-bonding region 113. It becomes possible to guide.

  Specifically, as shown in FIG. 15, during the heat treatment for bonding the semiconductor element 120 to the substrate 110, the organic solvent OS accumulates in the bottom space 152 of each groove 151, and passes through the bottom space 152. The non-bonded region 113 is discharged. In this case, since the groove cross-sectional area gradually decreases toward the groove bottom in each groove 151 that forms a wave shape, a bottom space 152 for storing the organic solvent OS can be formed at the groove bottom of each groove 151. . Further, since the organic solvent OS is decomposed by the heat treatment, the metal nanoparticles MN in the metal nanopaste are sintered and solidified while entering the bottom space 152 in the joining process. Therefore, the effect of increasing the bonding strength, the so-called “anchor effect” can be obtained. Further, the structure in which the organic solvent OS is removed makes it difficult for the organic solvent OS to remain at the bonding interface, and the generation ratio of voids (minute cavities and pores) at the bonding interface can be suppressed. As a result, the bonding area between the substrate 110 and the bonding layer 130 can be increased, so that the bonding strength is increased, the heat dissipation characteristics are improved, and the fatigue life is improved. These effects were confirmed by the following evaluation method.

(Tensile fracture strength measurement)
In order to verify that the concavo-convex structure 150 having the above configuration increases the bonding strength, the present inventor performed a tensile fracture strength measurement as shown in FIG. Specifically, two test pieces TP1 and TP2 having the same dimensions (length: 10 [mm], width: 20 [mm], plate thickness: 1.5 [mm]) made of oxygen-free copper are prepared, A joining region 112 which is an overlapping portion of these test pieces TP1 and TP2 is joined with a joining material. Thereby, the joined body TP in which the two test pieces TP1 and TP2 are integrally joined via the joining layer 130 is obtained. In this joined body TP, the area of the joining region 112 (joining area) is set to 100 [mm ² ], and the joining region 112 of the two test pieces TP1 and TP2 has a concavo-convex structure 150 (waviness shape). A plurality of grooves 151) are provided.

  Then, each of the two test pieces TP1 and TP2 is clamped by a testing machine, and a predetermined pulling speed (for example, a direction indicated by a white arrow) is separated from each other along the extending plane of the test pieces TP1 and TP2. The tensile load is calculated when the bonding layer 130 is broken. This tensile load is converted into a strength per area of the joining region 112 (hereinafter also referred to as “joining strength”). As a result, a result as shown in FIG. 17 was obtained. According to FIG. 17, the bonding strength was 6.4 [MPa] in the case of the base structure, whereas it was 15.7 [MPa] in the case of the concavo-convex structure 150. Based on this measurement result, it was confirmed that the bonding strength was actually increased by the effect of the waviness shape of each groove 151 described above.

(Void evaluation)
The present inventor conducted an internal inspection of the bonding layer 130 of the bonded body TP using an X-ray and an optical microscope (SEM) in order to verify that the uneven structure 150 having the above configuration suppresses the generation of voids. . Specifically, as shown in FIG. 18, for the internal inspection of the bonding layer 130 by X-rays, the bonding region 112 is photographed from above as indicated by the white arrow in the figure, and the photographing result is obtained. Based on this, the number and size of voids included in the predetermined region were measured. For the internal inspection of the bonding layer 130 using an optical microscope, the bonded body TP was cut along the BB line cross section and the CC line cross section in the figure, and the number and size of voids included in the cut surface were measured. As a result, a result as shown in FIG. 19 was obtained. According to FIG. 19, the ratio of voids contained in the bonding layer 130 (void ratio) was 2.3 [%] in the case of the base structure having a flat surface, whereas the uneven structure 150 The case was 0.4 [%]. Based on this internal inspection result, it was confirmed that the bonding strength can be increased by adopting the above-described waviness shape. Based on these internal inspection results, it was confirmed that the occurrence of voids can be suppressed by adopting the above-described wavy shape.

  In the concavo-convex structure 150 described above, a case has been described in which a plurality of linear grooves 151 processed by a femtosecond laser are arranged in parallel to each other. However, in the present invention, the shape of the grooves constituting the concavo-convex structure is described. The arrangement is not limited to this. For example, a configuration in which a plurality of linear grooves intersect, a configuration using one or a plurality of curved grooves, a configuration combining one or a linear groove and one or a plurality of curved grooves, etc. You can also.

  Furthermore, another embodiment of the uneven structure shown in FIGS. 20 to 22 may be employed as a specific example. For example, the concavo-convex structure 250 shown in FIG. 20 is configured using a plurality of grooves 251 that continuously extend from the center of the bonding region 112 to the non-bonding region 113. Further, the concavo-convex structure 350 shown in FIG. 21 is configured using a plurality of grooves 351 extending in a radial spiral continuously from the center of the bonding region 112 to the non-bonding region 113. Further, the concavo-convex structure 450 shown in FIG. 22 is configured by using a plurality of grooves 451 arranged so as to spread concentrically around the central portion of the bonding region 112. The plurality of grooves 451 may be configured by grooves extending only in the bonding region 112, or extending over both the bonding region 112 and the non-bonding region 113. And a groove to be formed. In the concavo-convex structure 250, 350, 450, as in the concavo-convex structure 150, at least one of the first cross-sectional structure and the second cross-sectional structure described above can be adopted. Even when these concavo-convex structures 250, 350, 450 are employed, the same operational effects as those obtained when the concavo-convex structure 150 is employed can be obtained. In general, the organic solvent remains in the vicinity of the center of the bonding region 112 and voids are easily formed. Therefore, as a means for discharging the organic solvent, the radial groove 251, the radial spiral groove 351, and the bonding region 112 and When the groove 451 extending over both regions of the non-bonding region 113 is used, the effect of suppressing the void generation ratio becomes higher.

  It should be noted that a configuration in which the shape (R portion) of the outer peripheral portion of the bonding layer is characterized as in the semiconductor devices 100 and 200 described above, and a surface structure (uneven structure) on the substrate as in the semiconductor device 300 described above. Of course, it is possible to combine with a configuration having characteristics. In this case, at least the thermal stress mitigating effect obtained by the shape characteristic of the outer peripheral portion of the bonding layer and the thermal stress mitigating effect obtained by the surface structure feature on the substrate are combined to reduce the thermal stress at the bonding interface. It becomes possible to further improve the mitigation effect.

  By the way, when the semiconductor device 100 is used under a severe temperature use environment ranging from a low temperature region to a high temperature region, thermal stress (thermal strain) easily accumulates due to repeated stress due to contraction and expansion of the bonding layer 130, and thus the bonding layer 130. There is a possibility that a fine crack is generated in the vicinity of the central portion of the film, and this crack further develops. In such a case, the semiconductor element 120 may be peeled off or peeled off due to a decrease in the bonding area between the semiconductor element 120 and the bonding layer 130.

  Therefore, the present inventor can further improve the concavo-convex structure shown in FIG. 12 and FIG. 20 to FIG. 22, even if the semiconductor device 100 is used in a severe temperature environment. It has been found that an excellent stress relaxation structure capable of obtaining a stress relaxation effect can be realized. For this stress relaxation structure, reference is made to FIGS.

  The concavo-convex structure 550 shown in FIG. 23 corresponds to the stress relaxation structure, and includes a plurality of connection grooves 153 in addition to the plurality of grooves 151 of the concavo-convex structure 150 shown in FIG. The connection groove 153 corresponds to the “connection groove” of the present invention. Each connection groove 153 extends linearly so as to connect the grooves 151 and 151 adjacent to each other in the bonding region 112 on the substrate 110 in a direction intersecting with the groove (a direction orthogonal in FIG. 23), and The groove cross section (cross-sectional view taken along the line DD in FIG. 23) in the direction intersecting with the extending direction (extending direction of the groove 151) is a waviness shape of micrometer order as shown in FIG. 25 (shown in FIG. 13). A sinusoidal waveform similar to the shape). In the example shown in FIG. 23, all of the connection grooves 153 extend so as to be parallel to each other, and a grid-like groove pattern is formed on the upper surface 111 of the substrate 110 by the grooves 151 and the connection grooves 153. . In this case, the groove 151 connects the connection grooves 153 and 153 adjacent to each other, and the groove 151 can also be referred to as a “connection groove” with respect to the connection groove 153.

  The concavo-convex structure 650 shown in FIG. 24 corresponds to the stress relaxation structure, and includes a plurality of connection grooves 253 in addition to the plurality of grooves 251 of the concavo-convex structure 250 shown in FIG. This connection groove 253 corresponds to the “connection groove” of the present invention. Each connection groove 253 extends in a circular shape so as to connect the grooves 251 and 251 adjacent to each other in the bonding region 112 on the substrate 110 in a direction intersecting the groove (circumferential direction in FIG. 23). Further, the groove cross section (cross section taken along the line EE in FIG. 24) in the direction intersecting with the extending direction of the plurality of connection grooves 253 (extending direction of the groove 251) is of the order of micrometers as shown in FIG. A wavy shape (sine waveform similar to the shape shown in FIG. 13) is formed. In the example shown in FIG. 24, all of the connection grooves 253 are arranged so as to extend concentrically around the center portion of the bonding region 112, and the spider webs are formed on the upper surface 111 of the substrate 110 by the grooves 251 and the connection grooves 253. A groove pattern is formed. In this case, the groove 251 connects the connection grooves 253 and 253 adjacent to each other, and the groove 251 can also be referred to as a “connection groove” with respect to the connection groove 253.

  According to the connection grooves 153 and 253 having the above configuration, even when the semiconductor device 100 is used in a severe temperature environment, a fine crack is generated in the vicinity of the center portion of the bonding layer 130. Can be prevented from progressing. Specifically, as shown in FIG. 26, when the cooling cycle in which the use temperature condition is changed from the low temperature region to the high temperature region within a unit time is repeated a plurality of times, the diameter from the central portion of the bonding layer 130 is increased. There are cases where voids V that are voids are formed along the circumferential direction at a plurality of positions toward the outside in the direction. That is, the void region by the void V may be formed concentrically as shown by a two-dot chain line in FIG. Such voids V are formed by the cracks extending in the circumferential direction due to the circumferential thermal stress accumulated in the bonding layer 130.

  Therefore, in the concavo-convex structure 650 of the present embodiment, in order to cope with this, each connection groove 253 is configured to extend in the circumferential direction, which is the crack propagation direction in the bonding layer 130 (see FIG. 25). ). In this case, in the groove cross section of the connection groove 253, for example, the distance D4 between two adjacent convex portions is approximately 60 [μm] or less, and the height (the depth of the concave portion) D5 of the convex portion is approximately 20 to 30 [ μm], and includes a wavy shape that changes the height of the groove with regular periodicity (a shape in which a wavy line passing through the groove top and bottom in the groove cross section continues periodically (sinusoidal waveform)). . As a result, the thermal stress acting in the circumferential direction of the bonding layer 130 (driving force of cracks that are to be connected in the circumferential direction) can be applied in a plurality of directions (for example, arbitrary in the undulation (wave) depending on the undulation shape of the connection groove 253 The normal vector direction at the point) can be reliably dispersed. As a result, even if the cooling / heating cycle is repeated a plurality of times, it becomes possible to suppress or delay the progress of cracks in the bonding layer 130, thereby providing the effect of improving the thermal life. In the case where the crack propagation direction in the bonding layer 130 is other than the circumferential direction, it is preferable to set the extending direction of the connection groove 253 so as to match the growth direction. In addition, in place of or in addition to the form in which the wavy shape is formed in the groove cross section of the connection groove 253 along the line E-E in FIG. 24, the groove cross section in the extending direction (circumferential direction) of the connection groove 253 is similar. A form in which a wavy shape is formed can also be adopted.

  The above-described effects have been actually confirmed by a cooling / heating cycle test by the present inventor. In this thermal cycle test, first, two test pieces of the same dimensions (length: 10 [mm], width: 20 [mm], plate thickness: 1.5 [mm]) made of oxygen-free copper were prepared. Groove processing for providing the groove 251 and connection groove 253 shown in FIG. 24 was performed on the upper surface of the evaluation test piece, and such groove processing was not performed on the other test piece for comparison. Thereafter, a bonded body in which the semiconductor elements were integrally bonded to each test piece via the bonding layer 130 was produced. After these two types of bonded bodies were subjected to a predetermined number of times of cooling and heating cycles, the void state inside the bonding layer in each bonded body, specifically, the void ratio (void ratio) was measured by X-ray. Moreover, the joining state of the semiconductor element in each joined body was examined by an optical microscope (SEM). As a result of measurement by X-ray, cracks developed in the comparative test piece as the cooling cycle was repeated and the void ratio increased to about 2 to 5 times the initial state, whereas in the test piece for evaluation, the void ratio was It was confirmed that the initial state was maintained without changing from the initial state. Thereby, it can be inferred that a good bonding state by the bonding layer is maintained even in a thermal cycle test with severe temperature conditions. On the other hand, as a result of inspection with an optical microscope, no cracks, cracks, destruction, etc. of the semiconductor elements themselves were confirmed in any of the semiconductor elements joined to any test piece.

  In addition, according to the connection grooves 153 and 253 having the above-described structure, the direction in which the organic solvent can be guided in the structure in which the organic solvent is guided from the bonding region 112 to the non-bonding region 113 using the plurality of grooves 151 and 251. Can be increased. As a result, even if an organic solvent stays and remains in any groove 151, 251, the organic solvent is guided to another groove 151, 251 through the connection groove 153, 253, and then non-through through this another groove 151, 251. It can be reliably guided to the bonding region 113. For example, in the case of the concavo-convex structure 650 shown in FIG. 24, as shown in FIG. 27, in addition to or instead of the original guide route R1 (route indicated by the dashed arrow) as the guide route for the organic solvent in any groove 251 Thus, guide routes R2 and R3 (routes indicated by solid arrows) connected to the adjacent grooves 251 through the connection grooves 253 can be used. In short, a multidirectional guide route can be formed by branching a unidirectional guide route. In this case, it is possible to suppress the generation ratio of voids generated in the bonding layer 130 due to the residual organic solvent. As a result, the bonding area of the bonding layer 130 with respect to each of the substrate 110 and the semiconductor element 120 can be prevented from decreasing and the bonding strength from being deteriorated. Further, even in a severe temperature use environment, a fine crack is generated in the vicinity of the center portion of the bonding layer 130, and further, the heat resistance can be improved by preventing the crack from progressing.

  The connection grooves 153 and 253 having the above-described configuration are preferably formed by laser processing in which a waviness shape on the order of micrometers is irradiated with a femtosecond laser onto the upper surface 111 of the substrate 110 as in the grooves 151 and 251. According to this laser processing, it is possible to reliably form a waviness shape on the order of micrometers in the connection grooves 153 and 253. In this case, a groove structure in which the center side end portions of the plurality of grooves 251 and the plurality of connection grooves 253 are not concentrated at one point (a structure in which the groove closest to the center portion is circular) as in the concavo-convex structure 650 in FIG. ), It is possible to prevent the laser light from being repeatedly irradiated to one point on the substrate 110 during laser processing, and as a result, problems such as holes in the substrate 110 are less likely to occur.

  Moreover, it is preferable that all of the connection grooves 153 and 253 having the above-described configuration extend continuously from the bonding region 112 to the non-bonding region 113 where the bonding material is not applied on the substrate 110. Thereby, in addition to the 1st function which connects the some groove | channel 151,251, the connection groove | channels 153 and 253 remove the organic solvent contained in the metal nano paste which is a joining material from the joining area | region 112 to the non-joining area | region 113. The second function of guiding to can be performed. In particular, when both the grooves 151 and 251 and the connection grooves 153 and 253 extend continuously from the bonding region 112 to the non-bonding region 113, the two types of grooves cooperate to include the metal nano paste. The function of guiding the organic solvent to the non-bonding region 113 can be enhanced.

  The present invention is not limited to the above exemplary embodiment, and various applications and modifications are possible. For example, each of the following embodiments to which the above embodiment is applied can be implemented.

  In the above embodiment, an example in which all corners of the outer peripheral portion of the bonding layer are excluded has been described. However, in the present invention, if at least one R portion is provided in the outer peripheral portion of the bonding layer, A thermal stress relaxation effect can be obtained. Therefore, if necessary, for example, a structure including both a corner portion and an R portion on the outer peripheral portion of the bonding layer may be employed.

  In the above embodiment, the grid-like groove pattern shown in FIG. 23 and the cobweb-like groove pattern shown in FIG. 24 formed on the substrate by the combination of the groove and the connection groove are described. Is not limited to these, and various groove patterns can be adopted as necessary. For example, a groove pattern in which a plurality of grooves 151 shown in FIG. 12 and a plurality of connection grooves 253 shown in FIG. 24 are combined may be employed.

  In the above embodiment, the groove and the connection groove on the substrate are both described in the case of forming a concavo-convex structure by making the groove cross section waviness shape (sinusoidal waveform) on the order of micrometers. When forming a groove or connection groove, the groove section has a wavy shape other than a micrometer order, or the groove cross section has a shape other than a wavy shape, for example, a wavy shape other than a wavy shape or a rectangular shape (non-sinusoidal waveform). Can also be adopted. Further, the number and shape of the grooves and connection grooves on the substrate can be appropriately changed according to the shape of the bonding layer.

  DESCRIPTION OF SYMBOLS 100 ... Semiconductor device, 110 ... Board | substrate, 120 ... Semiconductor element (semiconductor chip), 130 ... Bonding layer, 131 ... R part, 140 ... Shape maintenance mechanism, 141 ... Liquid-repellent part, 143 ... Receiving groove, 150, 250, 350 , 450, 550, 650 ... uneven structure, 151, 251, 351, 451 ... groove, 153, 253 ... connection groove

Claims (15)

A metal substrate, and a semiconductor element bonded to the substrate through a bonding layer made of only a bonding material applied to a bonding region on the substrate,
A semiconductor device, wherein a shape of an outer peripheral portion of the bonding layer is configured by an R portion having a predetermined radius of curvature. The semiconductor device according to claim 1,
The semiconductor device, wherein the bonding layer has a cylindrical shape, and an arc radius of the cylindrical shape corresponds to the predetermined curvature radius of the R portion. The semiconductor device according to claim 1 or 2,
The bonding layer is formed by heating after the bonding material having heat fluidity is applied to the bonding region,
A semiconductor device comprising a shape maintaining mechanism for maintaining the shape of the bonding material before and after heating. The semiconductor device according to claim 3,
The shape maintaining mechanism is a semiconductor device which is formed on the substrate so as to partition around the bonding region, and is configured by a concavo-convex structure of nanometer order having a liquid repellent effect on the bonding material. The semiconductor device according to claim 4,
The uneven structure is a semiconductor device formed by laser processing that irradiates a femtosecond laser on the substrate. A semiconductor device according to any one of claims 1 to 5,
The semiconductor element is bonded to the substrate via an auxiliary bonding layer made of only the bonding material in addition to the bonding layer, and the auxiliary bonding layer is disposed in the vicinity of the R portion in the outer peripheral portion of the bonding layer. A semiconductor device. A semiconductor device according to any one of claims 1 to 6,
A semiconductor device comprising an uneven structure in the bonding region on the substrate. The semiconductor device according to claim 7,
A semiconductor device comprising a groove extending in a long shape in the bonding region on the substrate and having a corrugated cross section of the order of micrometers, and the concavo-convex structure is constituted by the wavy shape of the groove. The semiconductor device according to claim 8,
The groove extends continuously from the bonding region to a non-bonding region where the bonding material is not applied on the substrate. The semiconductor device according to claim 9,
A semiconductor device, wherein a plurality of the grooves extend radially from the center of the bonding region to the non-bonding region. A semiconductor device according to any one of claims 8 to 10,
The groove is a semiconductor device formed by laser processing that irradiates a femtosecond laser on the substrate. The semiconductor device according to any one of claims 9 to 11, further comprising:
The semiconductor device provided with the connection groove | channel which connects the said adjacent groove | channels in the said junction area | region on the said board | substrate. The semiconductor device according to claim 12,
A semiconductor device, wherein the connection groove has a wavy cross section. The semiconductor device according to claim 13,
A semiconductor device, wherein a plurality of the connection grooves are arranged so as to extend concentrically around a central portion of the junction region. A semiconductor device according to any one of claims 12 to 14,
The connection groove is a semiconductor device that continues from the bonding region to a non-bonding region where the bonding material is not applied on the substrate.

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