Humidity detection element, semiconductor device, semiconductor module, electric power conversion device, and method of manufacturing humidity detection element

Abstract

To suppress an electrode and a humidity sensing layer of a humidity detection element from peeling from each other owing to change in ambient humidity and temperature.SOLUTION: A humidity detection element (30) comprises a first electrode layer (3) provided on a substrate, a humidity sensing layer (4) which is provided on the first electrode layer (3) and varies in dielectric constant with humidity, and a second electrode layer (5) which is provided on the humidity sensing layer (4). The top surface of the first electrode layer (3) has larger arithmetic means roughness than the boundary surface between the humidity sensing layer (4) and second electrode layer (5).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a humidity detection element, and particularly to a humidity detection element, a power conversion device, and a method for manufacturing the same, which have improved reliability against changes in humidity and temperature.

Background Art

[0002] As a conventional humidity detection element, for example, Patent Document 1 below discloses a capacitive humidity sensor having a structure in which a humidity-sensitive layer whose dielectric constant changes according to humidity is interposed between two opposing electrodes, and detecting humidity based on the capacitance between the two electrodes that changes according to the ambient humidity. The capacitance of a capacitor depends on the parameters represented by C = ε × S / L. Here, ε is the dielectric constant of the humidity-sensitive layer, S is the area of the two opposing electrodes, and L is the distance between the two electrodes.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A humidity detection element is placed in an environment where the surrounding humidity and temperature change. Further, in order to improve the detection sensitivity of the humidity detection element, as can be seen from the above-described capacitance (C) calculation formula, it is effective to increase the electrostatic capacitance of the humidity detection element by increasing the area (S) of the electrodes or decreasing the distance (L) between the two electrodes. However, when the area of the electrodes is increased, when changes in humidity and temperature occur, the stress caused by the difference in the linear expansion coefficients of the electrodes and the humidity-sensitive layer increases, and peeling is likely to occur between the electrodes and the humidity-sensitive layer, so the reliability of the humidity detection element tends to decrease.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to suppress peeling between an electrode and a humidity-sensitive layer caused by changes in ambient humidity and temperature in a humidity detection element.

Means for Solving the Problems

[0006] The humidity detection element according to the present disclosure includes a first electrode layer provided on a substrate, a humidity-sensitive layer provided on the first electrode layer and having a dielectric constant that changes with humidity, and a second electrode layer provided on the humidity-sensitive layer, and an arithmetic mean roughness of an upper surface of the first electrode layer is larger than an arithmetic mean roughness of an interface between the humidity-sensitive layer and the second electrode layer.

Effects of the Invention

[0007] According to the humidity detection element of the present disclosure, peeling between the first and second electrode layers and the humidity-sensitive layer is suppressed, and the reliability of the humidity detection element is improved.

Brief Description of the Drawings

[0008]

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Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the technology according to the present disclosure will be described with reference to the drawings. The following embodiments are merely examples, and not all of the things shown in the description of the embodiments are essential to the technology. Also, the drawings are schematic, and the sizes and positions of the components shown in the drawings are not necessarily accurate. Also, since the same reference numerals are given to the same components in a plurality of drawings, redundant descriptions thereof may be omitted. Also, in the present disclosure, the description of a certain component "comprising", "including" or "having" is not an exclusive expression excluding the existence of other components, unless otherwise specified.

[0010] Also, in the present disclosure, terms (for example, "first...", "second...", etc.) that mean ordinal numbers may be attached to the names of components, but these ordinal numbers are for convenience in order to facilitate understanding of the present disclosure, and unless otherwise specified, they do not particularly limit, for example, the order of arrangement or the order of manufacturing processes to a specific order.

[0011] <Embodiment 1> FIG. 1 and FIG. 2 are diagrams schematically showing an example of the configuration of the humidity detection element 30 according to Embodiment 1. FIG. 1 is a cross-sectional view of the humidity detection element 30, and FIG. 2 is a top view of the humidity detection element 30. The cross-sectional view along the line A1 - A2 shown in FIG. 2 corresponds to FIG. 1.

[0012] As shown in FIGS. 1 and 2, the humidity detection element 30 according to Embodiment 1 is configured by a laminated structure formed on the upper main surface (hereinafter referred to as the "upper surface") of the semiconductor substrate 1, and includes an insulating film 2, a first electrode layer 3, a humidity-sensitive layer 4, and a second electrode layer 5. That is, on the semiconductor substrate 1, the insulating film 2, the first electrode layer 3, the humidity-sensitive layer 4, and the second electrode layer 5 are laminated in this order in the thickness direction of the semiconductor substrate 1.

[0013] As the thickness of each layer of the laminated structure, for example, the insulating film 2 is 500 nm, the first electrode layer 3 is 500 nm, the humidity-sensitive layer 4 is 300 nm, and the second electrode layer 5 is 500 nm. The humidity-sensitive layer 4 is a material whose dielectric constant changes with humidity. For example, a polymer organic material such as polyimide or cellulose acetate can be used. The first electrode layer 3 and the second electrode layer 5 facing each other through the humidity-sensitive layer 4 function as electrodes for humidity detection, and the change in the dielectric constant of the humidity-sensitive layer 4 according to humidity is detected as a change in the capacitance between the first electrode layer 3 and the second electrode layer 5, thereby measuring the humidity.

[0014] Note that the material of the semiconductor substrate 1 may be silicon (Si) or a wide-bandgap semiconductor such as silicon carbide (SiC). Examples of wide-bandgap semiconductors include gallium nitride (GaN)-based materials and diamond in addition to silicon carbide.

[0015] The positional relationship in plan view of the first electrode layer 3, the humidity-sensitive layer 4, and the second electrode layer 5 as shown in FIG. 2 is preferably designed in consideration of the positional accuracy of the resist photomask formed by photolithography technology.

[0016] Hereinafter, the manufacturing method of the humidity detection element 30 according to Embodiment 1 will be described with reference to FIGS. 3 to 13.

[0017] First, as shown in FIG. 3, for example, a semiconductor substrate 1 which is an n-type Si substrate is prepared. Then, an insulating film 2 is formed on the upper surface of the semiconductor substrate 1. After that, as shown in FIG. 4, a first electrode layer 3 is formed on the insulating film 2. For the formation of the first electrode layer 3, for example, a vacuum evaporation method or a sputtering method can be used. As the material of the first electrode layer 3, for example, gold, aluminum, and aluminum alloys can be used.

[0018] Next, a photosensitive resin such as photoresist is applied onto the first electrode layer 3 by a coating method such as spin coating. By photolithography technology, the pattern of the photomask is transferred onto the photoresist to form a resist mask on the first electrode layer 3 (not shown). Then, by etching using the resist mask, as shown in FIG. 5, the surplus portion of the first electrode layer 3 is removed.

[0019] When the removal of the first electrode layer 3 is performed by dry etching, by appropriately adjusting the dry etching conditions such as the flow rate and pressure of the etching gas containing chlorine, bromine, etc., as shown in FIG. 6, the end portion of the first electrode layer 3 can be made into a tapered shape. Also, if the removal of the first electrode layer 3 is performed by wet etching using an etching solution containing phosphoric acid, nitric acid, acetic acid, etc., as shown in FIG. 7, the end portion of the first electrode layer 3 can be made into an isotropic shape. Here, the description will continue assuming that the end portion of the first electrode layer 3 is processed into an isotropic shape as shown in FIG. 7.

[0020] Next, for the structure shown in FIG. 7, by performing a heat treatment of heating at a temperature of 150°C or higher and 400°C or lower for 15 minutes or more, as shown in FIG. 8, unevenness is formed on the surface of the first electrode layer 3. The method of forming the unevenness is not limited to heat treatment, and for example, a dry etching technique using a plasma containing argon or fluorine can also be used. By using heat treatment and plasma treatment in combination, the surface unevenness can be controlled more preferably.

[0021] Thereafter, a humidity-sensitive layer 4 having a property that its dielectric constant changes with humidity is formed so as to cover the first electrode layer 3. For example, when photosensitive polyimide is used as the humidity-sensitive layer 4, after applying the photosensitive polyimide onto the first electrode layer 3 by a spin coating method or the like, patterning is performed by photolithography technology, whereby a humidity-sensitive layer 4 covering the first electrode layer 3 can be formed as shown in FIG. 9. The humidity-sensitive layer 4 does not necessarily have to be a photosensitive material. In that case, after applying the material of the humidity-sensitive layer 4 by a spin coating method or the like, the material is patterned by selective etching using photolithography technology, whereby the structure of FIG. 9 can be obtained.

[0022] Next, with respect to the structure of FIG. 9, for example, heat treatment is performed at 200°C or higher and 400°C or lower, more preferably 250°C or higher and 380°C or lower, whereby the upper end portion of the humidity-sensitive layer 4 is made into a round shape as shown in FIG. 10. As a method for obtaining this round shape, a dry etching technology using plasma containing oxygen and argon can also be used.

[0023] Next, a photosensitive resin such as photoresist is applied onto the upper surface of the semiconductor substrate 1 including the insulating film 2, the first electrode layer 3, and the humidity-sensitive layer 4 by a spin coating method or the like. By transferring the pattern of the photomask to the photoresist by photolithography technology, a patterned resist mask is formed on the insulating film 2, the first electrode layer 3, and the humidity-sensitive layer 4. An opening is provided in this resist mask in a region where the second electrode layer 5 to be formed in the next step is desired to be left.

[0024] Then, a metal layer to be the second electrode layer 5 is formed on the entire surface of the semiconductor substrate 1 including on the resist mask. For forming the metal layer, for example, a vacuum evaporation method or a sputtering method can be used. As the material of the metal layer, for example, gold, aluminum, and aluminum alloy can be used. Thereafter, the resist mask is removed by a chemical solution, and the metal layer on the resist mask is removed by a lift-off method to pattern the metal layer. As shown in FIG. 11, the remaining metal layer at this time becomes the second electrode layer 5.

[0025] When forming the second electrode layer 5, in order to prevent unnecessary connection between the first electrode layer 3 and the second electrode layer 5, it is preferable to remove the residue of the metal layer by using dry etching technology or wet etching technology. Further, when this process is carried out, as shown in FIG. 12, the upper end portions of the first electrode layer 3, the humidity-sensitive layer 4, and the second electrode layer 5 become round-shaped, and the generation of cracks in each layer due to external force can be suppressed, so it is more preferable. In this way, the humidity detection element 30 shown in FIGS. 1 and 2 can be obtained.

[0026] Here, the arithmetic surface roughness, which is an index of the surface roughness, will be described. FIG. 13 is a diagram for explaining the definition of the arithmetic mean roughness. The arithmetic mean roughness (Ra) defined in Japanese Industrial Standards (JIS B 0601:1994, JIS B 0031:1994) is obtained by extracting an interval having a reference length (l) in the direction of the mean line 401 from a curve 400 corresponding to the unevenness of the surface (hereinafter referred to as "roughness curve"), and is defined as the average value of the distances from the mean line 401 to the roughness curve 400 in that interval. That is, when the direction of the mean line 401 in the interval is the X-axis, the direction of the vertical magnification is the Y-axis, and the reference length is l, the arithmetic mean roughness Ra is obtained by the calculation formula described in FIG. 13.

[0027] The inventors of the technology according to the present disclosure performed a 1 mm line scan using an atomic force microscope (AFM) (SPM-9600 manufactured by Shimadzu Corporation) on the upper surface of the first electrode layer 3 (that is, the interface between the first electrode layer 3 and the humidity-sensitive layer 4) and the lower surface of the second electrode layer 5 (that is, the interface between the humidity-sensitive layer 4 and the second electrode layer 5) in the humidity detection element 30 (FIGS. 1 and 2) of the present embodiment to obtain roughness curves, and calculated their arithmetic mean roughnesses (Ra). As a result, in the humidity detection element 30 of the present embodiment, it was confirmed that the upper surface of the first electrode layer 3 has a larger arithmetic mean roughness than the lower surface of the second electrode layer 5. This is because, as described with reference to FIG. 8, unevenness was formed on the surface of the first electrode layer 3 by heat treatment.

[0028] Further, the inventors prepared samples of a plurality of humidity detection elements 30 by changing the conditions of the heat treatment for forming irregularities on the surface of the first electrode layer 3, and for each sample, a storage test (so-called "8585 test") was conducted for 1000 hours in an environment of a temperature of 85°C and a relative humidity of 85%. Then, each sample after the 8585 test was observed with an optical microscope to observe the presence or absence of peeling between the first electrode layer 3, the second electrode layer 5, and the humidity-sensitive layer 4. The results are shown in FIG. 14.

[0029] As can be seen from FIG. 14, in samples (samples 1 and 2) where the arithmetic mean roughness of the upper surface of the first electrode layer 3 was equal to or less than the arithmetic mean roughness of the lower surface of the second electrode layer 5, peeling occurred between the first electrode layer 3, the second electrode layer 5, and the humidity-sensitive layer 4 after the 8585 test. However, in samples (samples 3, 4, and 5) where the arithmetic mean roughness of the upper surface of the first electrode layer 3 was greater than the arithmetic mean roughness of the lower surface of the second electrode layer 5, that is, in the humidity detection element 30 of the present embodiment, no peeling was confirmed between the first electrode layer 3, the second electrode layer 5, and the humidity-sensitive layer 4 after the 8585 test.

[0030] In addition, when the capacitance of each sample was measured, the capacitance of samples 1 and 2 decreased significantly after the 8585 test, but the capacitance of samples 3, 4, and 5 hardly changed before and after the 8585 test. From this, it can also be inferred that no peeling occurred between the first electrode layer 3, the second electrode layer 5, and the humidity-sensitive layer 4 in samples 3, 4, and 5 after the 8585 test.

[0031] Note that the method for measuring the arithmetic mean roughness is not limited to the method described above, and for example, an arbitrary method such as a stylus type step and surface roughness meter or a laser microscope capable of non-contact measurement can be selected.

[0032] Thus, in the humidity detection element 30 of the present embodiment, the arithmetic mean roughness of the upper surface of the first electrode layer 3 is greater than the arithmetic mean roughness of the lower surface of the second electrode layer 5, thereby preventing peeling between the first electrode layer 3, the second electrode layer 5, and the humidity-sensitive layer 4, and improving the reliability of the humidity detection element 30.

[0033] When the arithmetic mean roughness of the upper surface of the first electrode layer 3 is large, the reason why peeling between the first electrode layer 3, the second electrode layer 5, and the humidity sensing layer 4 is suppressed is considered. First, it is considered that the peeling between the first electrode layer 3 and the humidity sensing layer 4 is suppressed because the connection between the first electrode layer 3 and the humidity sensing layer 4 is strengthened by the unevenness of the upper surface of the first electrode layer 3. In addition, since the first electrode layer 3 is restricted in its expansion and contraction by the semiconductor substrate 1, when the connection between the first electrode layer 3 and the humidity sensing layer 4 is strengthened, the expansion and contraction of the humidity sensing layer 4 is also suppressed. As a result, the stress generated between the second electrode layer 5 and the humidity sensing layer 4 is relaxed, and it is considered that peeling between the second electrode layer 5 and the humidity sensing layer 4 is also suppressed.

[0034] [Modification Example] FIGS. 15 and 16 are diagrams showing a modification example of the humidity detection element 30 according to Embodiment 1. FIG. 15 is a cross-sectional view of the humidity detection element 30, and FIG. 16 is a top view of the humidity detection element 30. A cross-sectional view taken along line B1 - B2 shown in FIG. 16 corresponds to FIG. 15.

[0035] The configurations of FIGS. 15 and 16 are such that an opening 5a is provided in the region of the second electrode layer 5 facing the humidity sensing layer 4 as compared with the configurations of FIGS. 1 and 2. The second electrode layer 5 having the opening 5a can be formed by adjusting the pattern of the region where the metal layer remains (specifically, the opening pattern of the resist mask used for lift-off of the metal layer) in the metal layer patterning process of the second electrode layer 5 described with reference to FIG. 11.

[0036] By providing the opening 5a in the second electrode layer 5, the area where the second electrode layer 5 contacts the humidity sensing layer 4 is reduced as compared with Embodiment 1. As a result, the area of the second electrode layer 5 facing the humidity sensing layer 4 is smaller than the area of the first electrode layer 3 facing the humidity sensing layer 4.

[0037] As the area of contact between the second electrode layer 5 and the humidity-sensitive layer 4 decreases, the stress generated between the humidity-sensitive layer 4 and the second electrode layer 5 due to the difference in the linear expansion coefficients is reduced. Further, as the area of the humidity-sensitive layer 4 that is exposed increases, the response speed of the humidity detection element 30 to changes in humidity becomes faster. However, it should be noted that the capacitance of the humidity detection element 30 decreases by the amount by which the area of the second electrode layer 5 decreases.

[0038] Furthermore, as shown in FIG. 17, a passivation layer 6 made of, for example, silicon oxide (SiO 2 ) or silicon nitride (SiN) may be provided so as to cover the second electrode layer 5. Thereby, the humidity detection element 30 becomes mechanically robust, and the reliability of the humidity detection element 30 against external stress is improved.

[0039] In the example of FIG. 17, the passivation layer 6 covers only the second electrode layer 5, but the passivation layer 6 may be formed so as to cover the insulating film 2, the first electrode layer 3, the humidity-sensitive layer 4, and the second electrode layer 5. In that case, it is necessary to provide openings in the passivation layer 6 in a region for connecting external wiring etc. to the first electrode layer 3 and the second electrode layer 5 and in a region necessary for the absorption and desorption of moisture by the humidity-sensitive layer 4.

[0040] <Embodiment 2> FIGS. 18 and 19 are diagrams schematically showing an example of the configuration of a semiconductor device 40 according to Embodiment 2. FIG. 18 is a top view of the semiconductor device 40, and FIG. 19 is a cross-sectional view of the semiconductor device 40. A cross-sectional view taken along line C1 - C2 shown in FIG. 18 corresponds to FIG. 19.

[0041] As shown in FIGS. 18 and 19, the semiconductor device 40 includes a semiconductor substrate 11 on which semiconductor elements are formed, a surface electrode 7 formed on the main surface (hereinafter referred to as the "upper surface" or "surface") on the upper side of the semiconductor substrate 11, a protective insulating film 9 covering a part of the surface electrode 7, and a humidity detection circuit 10 mounted on the surface electrode 7. Further, a back surface electrode 8 is provided on the main surface (hereinafter referred to as the "lower surface" or "back surface") on the lower side of the semiconductor substrate 11. The humidity detection circuit 10 is a circuit that detects the humidity around the semiconductor device 40 and is configured using the humidity detection element 30 described in the first embodiment.

[0042] In order to enable connection of external wiring or the like to the surface electrode 7, an opening that exposes the central portion of the surface electrode 7 is formed in the protective insulating film 9. In other words, the protective insulating film 9 is provided at the peripheral portion of the surface electrode 7. However, the protective insulating film 9 is also provided in the region where the humidity detection circuit 10 is disposed. Therefore, the humidity detection circuit 10 is mounted on the surface electrode 7 via the protective insulating film 9.

[0043] There is no restriction on the type of the semiconductor device 40. For example, semiconductor devices for power control such as MOSFET (Metal Oxide Semiconductor Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), and SBD (Schottky barrier diode) are assumed.

[0044] Note that the material of the semiconductor substrate 11 may be silicon (Si) or a wide bandgap semiconductor such as silicon carbide (SiC). A semiconductor device formed using a wide bandgap semiconductor is excellent in operation at high voltage, high current, and high temperature compared with a conventional semiconductor device using silicon and has characteristics suitable for a semiconductor device for power control.

[0045] Hereinafter, as a specific example of the semiconductor device 40 according to the second embodiment, a Schottky barrier diode made of a silicon carbide semiconductor (hereinafter referred to as "SiC-SBD") is shown, and its manufacturing method will be described.

[0046] FIG. 20 is a cross-sectional view of the SiC-SBD as the semiconductor device 40 of Embodiment 2. In FIG. 20, the semiconductor substrate 11 is composed of an n-type SiC semiconductor. On the semiconductor substrate 11, as a first epitaxial film, a first drift layer 12 made of n-type SiC is formed. Further, on the first drift layer 12, as a second epitaxial film, a second drift layer 13 made of n-type SiC is formed.

[0047] An interlayer insulating film 14 having an opening is formed on the second drift layer 13, and on it, a Schottky electrode layer 15 connected to the second drift layer 13 through the opening of the interlayer insulating film 14 is formed. The peripheral portion of the Schottky electrode layer 15 riding on the interlayer insulating film 14 functions as a field plate, thereby suppressing the concentration of an electric field under the end portion of the Schottky electrode layer 15. The surface electrode 7, the protective insulating film 9, and the humidity detection circuit 10 are formed on the Schottky electrode layer 15.

[0048] FIG. 21 is a flowchart showing an example of a manufacturing method of the SiC-SBD as the semiconductor device 40 of Embodiment 2. FIGS. 22 to 29 are explanatory diagrams of a manufacturing method of the SiC-SBD equipped with the humidity detection circuit according to the present embodiment. Hereinafter, the manufacturing method of the semiconductor device 40 will be specifically described with reference to the flowchart of FIG. 21 and FIGS. 22 to 29.

[0049] First, a semiconductor substrate preparation step (step S1) is performed. In this step, as shown in FIG. 22, on the upper surface of the semiconductor wafer which is the semiconductor substrate 11, the first drift layer 12 is formed by an epitaxial crystal growth method, and further, the second drift layer 13 is formed on the first drift layer 12. The formation of the second drift layer 13 is performed by an epitaxial crystal growth method at a growth temperature lower than the growth temperature of the first drift layer 12.

[0050] Next, the surface-side circuit formation step (step S2) is performed. In this step, first, as shown in FIG. 23, an interlayer insulating film 14 is formed on the upper surface of the second drift layer 13 by a deposition method such as thermal oxidation or chemical vapor deposition. Then, after forming a mask (not shown) made of resist or the like using photolithography technology, the interlayer insulating film 14 in the unnecessary region is removed as shown in FIG. 24 by dry etching using plasma or wet etching using a chemical solution. Further, the above mask is removed by plasma ashing or wet treatment.

[0051] In the second drift layer 13 in the portion facing the interlayer insulating film 14, an impurity layer such as ion implantation and activation is appropriately formed so that a desired breakdown voltage can be obtained for the SiC-SBD. When forming a p-type impurity layer, boron (B), aluminum (Al), or the like is used as the impurity. When forming an n-type impurity layer, phosphorus (P), nitrogen (N), or the like is used as the impurity.

[0052] Furthermore, wet treatment containing hydrofluoric acid or cleaning with a mixed solution of ammonia and hydrogen peroxide solution, a mixed solution of sulfuric acid and hydrogen peroxide solution, or a mixed solution of hydrochloric acid and hydrogen peroxide solution is appropriately performed. Then, a Schottky electrode layer 15 is formed so as to contact the second drift layer 13. As the material of the Schottky electrode layer 15, titanium (Ti), nickel (Ni), iridium (Ir), platinum (Pt), or the like can be appropriately selected.

[0053] Thereafter, the material of the Schottky electrode layer 15 formed in the surplus portion of the outer peripheral region is removed by patterning using photolithography and etching using plasma or a chemical solution. Then, in order to surely obtain electrical connection between the second drift layer 13 and the Schottky electrode layer 15, heat treatment is performed as necessary. By doing so, a cross-sectional structure as shown in FIG. 25 is obtained, and step S2 is completed.

[0054] Next, the surface electrode formation step (step S3) is performed. In this step, using aluminum, an aluminum alloy composed of aluminum and silicon, nickel, or the like, the surface electrode 7 is formed on the Schottky electrode layer 15 as shown in FIG. 26 by a sputtering method or a vapor deposition method or the like. Thereafter, the excess surface electrode 7 is removed by patterning by photolithography and etching using a plasma or a chemical solution. The surface electrode 7 is electrically connected to the second drift layer 13 via the Schottky electrode layer 15.

[0055] Next, the protective insulating film formation step (step S4) is performed. In this step, as shown in FIG. 27, the protective insulating film 9 is formed on the outermost periphery on the surface side of the SiC-SBD and in the region where the humidity detection circuit 10 is installed. The protective insulating film 9 covers a part of the upper surface of the surface electrode 7 and the portion where the upper surface of the second drift layer 13 is exposed. As the material of the protective insulating film 9, polyimide or silicone resin is preferable. Examples of the method for forming the protective insulating film 9 include a method of spin-coating the material and patterning it using photolithography and etching techniques, and a method of using an inkjet coating technique.

[0056] Next, the humidity detection circuit formation step (step S5) is performed. In this step, as shown in FIG. 28, the humidity detection circuit 10 is formed on the protective insulating film 9 formed on the surface electrode 7. The humidity detection element 30 constituting the humidity detection circuit 10 is formed by the manufacturing method described in the first embodiment.

[0057] Next, the wafer thinning step (step S6) is performed. In this step, in order to reduce the loss during energization, as shown in FIG. 29, the semiconductor substrate 11 is thinned. Specifically, the semiconductor substrate 11 is thinned (made thinner) by machining from the lower surface side of the semiconductor substrate 11 using, for example, a grinding wheel composed of alumina abrasive grains or diamond abrasive grains. Note that this step may be performed as necessary and may be omitted.

[0058] Next, the step of forming the back electrode (step S7) is performed. In this step, the back electrode 8 is formed on the lower surface (back surface) of the semiconductor substrate 11 using titanium, a titanium alloy, aluminum, an aluminum alloy composed of aluminum and silicon, or nickel. In order to prevent the back electrode 8 from being oxidized when soldering is performed on the back electrode 8, an antioxidant film made of gold, platinum, silver, or a silver alloy containing palladium may be formed on the outermost surface of the back electrode 8.

[0059] Thereafter, the plurality of semiconductor devices 40 formed on the semiconductor wafer are separated into individual pieces using a dicing device. Thereby, the semiconductor devices 40 shown in FIGS. 18 and 19 are obtained.

[0060] The semiconductor device 40 equipped with the humidity detection circuit 10 is incorporated into a semiconductor module 50 as illustrated in FIG. 30. In the semiconductor module 50 of FIG. 30, lead frames 19 are respectively connected to the upper surface and the lower surface of the semiconductor device 40 using, for example, solder 18. The semiconductor device 40 and the lead frames 19 are encapsulated with a molding resin 20 which is a sealing resin. However, a part of the lead frame 19 protrudes from the molding resin 20 as an external connection terminal.

[0061] Note that the semiconductor device 40 incorporated into the semiconductor module 50 does not necessarily have to be equipped with the humidity detection circuit 10. For example, as shown in FIG. 31, separately from the semiconductor device 40, a humidity detection element 30 may be mounted on the lead frame 19, and the humidity detection element 30 and the semiconductor device 40 may be encapsulated with the molding resin 20. In that case, it is not necessary for the semiconductor device 40 to be equipped with the humidity detection circuit 10.

[0062] In this way, by incorporating the conductor device 40 equipped with the humidity detection circuit 10, or the semiconductor device 40 and the humidity detection element 30 into the semiconductor module 50, it is possible to detect a high humidity state before a malfunction occurs due to conduction, discharge, or migration of the semiconductor device 40 caused by moisture or humidity that has entered the semiconductor module 50. Thereby, it becomes possible to prevent the above-mentioned malfunction in advance.

[0063] <Embodiment 3> This embodiment applies the humidity detection element 30 according to the above-described Embodiment 1 or the semiconductor device 40 equipped with the humidity detection circuit 10 according to Embodiment 2 to a power conversion device. The semiconductor device for power use is exemplified by a silicon carbide semiconductor device. Although the technology according to the present disclosure is not limited to a specific power conversion device, hereinafter, as the power conversion device in Embodiment 3, a three-phase inverter will be described in detail.

[0064] FIG. 32 is a block diagram schematically showing the configuration of a power conversion system to which the power conversion device 200 according to Embodiment 3 is applied. This power conversion system is composed of a power source 100, a power conversion device 200, and a load 300.

[0065] The power source 100 is a DC power source and supplies DC power to the power conversion device 200. The power source 100 can be configured by various things. For example, it can be configured by a DC system, a solar cell, a storage battery, or it may be configured by a rectifier circuit or an AC / DC converter connected to an AC system. Further, the power source 100 may be configured by a DC / DC converter that converts the DC power output from the DC system into a predetermined power.

[0066] The power conversion device 200 is a three-phase inverter connected between the power source 100 and the load 300. The power conversion device 200 converts the DC power supplied from the power source 100 into AC power and supplies it to the load 300. The power conversion device 200 has a main conversion circuit 201 and a control circuit 203. The main conversion circuit 201 converts the input DC power into AC power and outputs the AC power. The control circuit 203 outputs a control signal for controlling the main conversion circuit 201 to the main conversion circuit 201.

[0067] The load 300 is a three-phase motor driven by the AC power supplied from the power conversion device 200. Note that the load 300 is not limited to a specific application and is a motor mounted on various electrical devices. For example, it is used as a motor for hybrid vehicles, electric vehicles, railway vehicles, elevators, or air conditioning equipment.

[0068] Hereinafter, the details of the power conversion device 200 will be described. The main conversion circuit 201 includes switching elements and freewheeling diodes (not shown). By switching the switching elements, the main conversion circuit 201 converts the DC power supplied from the power source 100 into AC power and supplies it to the load 300. There are various specific circuit configurations of the main conversion circuit 201, but the main conversion circuit 201 according to the present embodiment is a two-level three-phase full-bridge circuit and can be composed of six switching elements and six freewheeling diodes connected in anti-parallel to each of the switching elements. As at least one of the switching elements and the freewheeling diodes of the main conversion circuit 201, a semiconductor device 202 combined with the humidity detection element 30 according to Embodiment 1, or a semiconductor device 202 equipped with the humidity detection circuit 10 according to Embodiment 2 (hereinafter, these are collectively referred to as "semiconductor device 202 equipped with humidity detection element") is applied. The six switching elements are connected in series in pairs of two switching elements to form upper and lower arms, and each upper and lower arm constitutes each phase (U phase, V phase, W phase) of the full-bridge circuit. Then, the output terminals of each upper and lower arm, that is, the three output terminals of the main conversion circuit 201, are connected to the load 300.

[0069] The main conversion circuit 201 also includes a drive circuit (not shown) that drives each switching element. The drive circuit generates a drive signal for driving the switching elements of the main conversion circuit 201 and supplies it to the control electrodes of the switching elements of the main conversion circuit 201. Specifically, in accordance with the control signal from the control circuit 203 described later, a drive signal for turning on the switching element and a drive signal for turning off the switching element are output to the control electrodes of each switching element. When maintaining the switching element in the on state, the drive signal is a voltage signal (on signal) equal to or higher than the threshold voltage of the switching element, and when maintaining the switching element in the off state, the drive signal is a voltage signal (off signal) equal to or lower than the threshold voltage of the switching element.

[0070] The control circuit 203 controls the switching elements of the main conversion circuit 201 so that the desired power is supplied to the load 300. Specifically, the control circuit 203 calculates the time (on time) for which each switching element of the main conversion circuit 201 should be in the on state based on the power to be supplied to the load 300. For example, the main conversion circuit 201 can be controlled by pulse width modulation (PWM) control that modulates the on time of the switching element according to the voltage to be output. Then, at each point in time, the control circuit 203 outputs a control command (control signal) to the drive circuit included in the main conversion circuit 201 so that an on signal is output to the switching element that should be in the on state and an off signal is output to the switching element that should be in the off state. The drive circuit outputs an on signal or an off signal as a drive signal to the control electrodes of each switching element in accordance with this control signal.

[0071] The manufacturing method of the power conversion device 200 has the following steps. By the manufacturing method described in the above-described embodiment or its modification, a semiconductor device 202 provided with a humidity detection element is manufactured. A main conversion circuit 201 having the semiconductor device 202 provided with this humidity detection element is formed. Also, a control circuit 203 is formed. By combining these, the power conversion device 200 is obtained. When the main conversion circuit 201 is formed, the drain electrode (corresponding to the back electrode 8 in the second embodiment) of the semiconductor device 202 provided with the humidity detection element is joined to the mounting substrate. Also, the source electrode (corresponding to the front electrode 7 in the second embodiment) of the semiconductor device 202 provided with the humidity detection element is joined to the mounting substrate via a wire.

[0072] According to the present embodiment, as at least one of the semiconductor devices constituting the main conversion circuit 201, a semiconductor device 202 provided with a humidity detection element is used. Thereby, while improving the reliability of the humidity detection element due to the intrusion of moisture from peripheral members, before an operation failure occurs due to conduction, discharge, or migration of the semiconductor device caused by moisture or humidity that has entered the semiconductor module, a high humidity state is detected, and an operation failure of the semiconductor device constituting the main conversion circuit 201 can be suppressed. Thereby, the reliability of the main conversion circuit 201 is enhanced. Therefore, the reliability of the power conversion device 200 can be enhanced.

[0073] In the present embodiment, an example in which the technology according to the present disclosure is applied to a two-level three-phase inverter has been described. However, the technology according to the present disclosure is not limited to this and can be applied to various power conversion devices. In the present embodiment, the power conversion device is a two-level power conversion device, but it may also be a multi-level power conversion device such as a three-level device. Also, when supplying power to a single-phase load, the technology according to the present disclosure may be applied to a single-phase inverter. Also, when supplying power to a DC load or the like, it is also possible to apply the technology according to the present disclosure to a DC / DC converter or an AC / DC converter.

[0074] In addition, the power conversion device to which the technology according to the present disclosure is applied is not limited to the case where the above-described load is an electric motor. For example, it can also be used as a power supply device for any of an electric discharge machine, a laser processing machine, an induction heating cooker, and a contactless power feeding system. Furthermore, it can also be used as a power conditioner for a photovoltaic power generation system or a power storage system, etc.

[0075] Note that it is possible to freely combine the respective embodiments or to appropriately modify or omit the respective embodiments.

[0076] <Appendix> Hereinafter, various aspects of the present disclosure will be collectively described as an appendix.

[0077] (Appendix 1) A first electrode layer provided on a substrate, A humidity-sensitive layer provided on the first electrode layer and having a dielectric constant that changes with humidity, A second electrode layer provided on the humidity-sensitive layer, Comprising, The arithmetic mean roughness of the upper surface of the first electrode layer is larger than the arithmetic mean roughness of the interface between the humidity-sensitive layer and the second electrode layer, Humidity detection element.

[0078] (Appendix 2) The area of the second electrode layer facing the humidity-sensitive layer is smaller than the area of the first electrode layer facing the humidity-sensitive layer, The humidity detection element according to Appendix 1.

[0079] (Appendix 3) Further comprising a passivation layer covering at least the second electrode layer, The humidity detection element according to Appendix 1 or Appendix 2.

[0080] (Appendix 4) A semiconductor device equipped with a humidity detection circuit including the humidity detection element according to any one of Appendices 1 to 3.

[0081] (Appendix 5) The semiconductor device described in Supplementary Note 4, a sealing resin for sealing the semiconductor device, and a semiconductor module including the same.

[0082] (Supplementary Note 6) a humidity detection element described in any one of Supplementary Notes 1 to 3, a semiconductor device encapsulated in a sealing resin together with the humidity detection element, and a semiconductor module including the same.

[0083] (Supplementary Note 7) a semiconductor device including a humidity detection element described in any one of Supplementary Notes 1 to 3, a main conversion circuit that converts input power and outputs the converted power, a control circuit that outputs a control signal for controlling the main conversion circuit to the main conversion circuit, and a power conversion device including the same.

[0084] (Supplementary Note 8) a step of forming a first electrode layer on a substrate, a step of forming irregularities on the upper surface of the first electrode layer, a step of forming a humidity-sensitive layer whose dielectric constant changes with humidity on the first electrode layer, a step of forming a second electrode layer on the humidity-sensitive layer, and a method for manufacturing a humidity detection element including the same.

Explanation of Reference Numerals

[0085] 1 semiconductor substrate, 2 insulating film, 3 first electrode layer, 4 humidity-sensitive layer, 5 second electrode layer, 5a opening, 6 passivation layer, 7 surface electrode, 8 back surface electrode, 9 protective insulating film, 10 humidity detection circuit, 11 semiconductor substrate, 12 first drift layer, 13 second drift layer, 14 interlayer insulating film, 15 Schottky electrode layer, 18 solder, 19 lead frame, 20 mold resin, 30 humidity detection element, 40 semiconductor device, 50 semiconductor module, 100 power supply, 200 power conversion device, 201 main conversion circuit, 202 semiconductor device including humidity detection element, 203 control circuit, 300 load.

Claims

1. a first electrode layer provided on a substrate; a humidity-sensitive layer provided on the first electrode layer and having a permittivity that changes with humidity; a second electrode layer provided on the humidity-sensitive layer; comprising: wherein an arithmetic mean roughness of an upper surface of the first electrode layer is greater than an arithmetic mean roughness of an interface between the humidity-sensitive layer and the second electrode layer; a humidity detection element.

2. wherein an area of the second electrode layer facing the humidity-sensitive layer is smaller than an area of the first electrode layer facing the humidity-sensitive layer; the humidity detection element according to Claim 1.

3. further comprising a passivation layer covering at least the second electrode layer; the humidity detection element according to Claim 1 or Claim 2.

4. a semiconductor device mounted with a humidity detection circuit including the humidity detection element according to Claim 1 or Claim 2; a semiconductor device.

5. the semiconductor device according to Claim 4; a sealing resin for sealing the semiconductor device; a semiconductor module comprising:

6. the humidity detection element according to Claim 1 or Claim 2; a semiconductor device sealed in a sealing resin together with the humidity detection element; a semiconductor module comprising:

7. having a semiconductor device including the humidity detection element according to Claim 1 or Claim 2, a main conversion circuit configured to convert input power and output the converted power, a control circuit configured to output a control signal for controlling the main conversion circuit to the main conversion circuit; a power conversion device comprising:

8. a step of forming a first electrode layer on a substrate; a step of forming irregularities on an upper surface of the first electrode layer; a step of forming a humidity-sensitive layer having a permittivity that changes with humidity on the first electrode layer; a step of forming a second electrode layer on the humidity-sensitive layer; a method for manufacturing a humidity detection element comprising:

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