JP6892997B2 - Semiconductor device - Google Patents

Description

The present invention relates to a semiconductor device having a resin-sealed mounting structure in which a semiconductor chip is sealed with a resin.

The characteristics of semiconductor chips that function as transistors and diodes are affected by surface contamination and static electricity. Further, the thin metal wire connected to the electrode arranged on the surface of the semiconductor chip is vulnerable to vibration or the like in the exposed state as it is. Therefore, in general, as described in Patent Document 1, for example, the semiconductor chip and its periphery are filled and sealed mainly with a resin-based insulating material.

Japanese Unexamined Patent Publication No. 2013-062540 Japanese Unexamined Patent Publication No. 2009-0997784

Tsunemasa Taguchi, "21st Century Lights with White LEDs", Journal of the Illuminating Engineering Institute of Japan, Vol. 85, No. 7, 2001, p. 496-501 Naoki Uchiyama, "Laser Dicing Technology for Completely Dry Processes", Journal of Precision Engineering, Vol. 76, No. 7, 2010, p. 747-750

When a forward current flows through the pn junction in such a semiconductor chip, light having energy corresponding to the band gap of the semiconductor forming the pn junction is generated in principle regardless of whether it is a direct transition type or an indirect transition type. The bandgap of silicon (Si) semiconductors is 1.12 eV, and the bandgap of gallium arsenide (GaAs) semiconductors is 1.43 eV. The shortest wavelengths of light emitted from these semiconductors are 1107 nm and 867 nm, respectively, both of which are red. It is outside light. Therefore, even if the generated light is applied to the sealing resin, only heat is generated.

On the other hand, the bandgap of silicon carbide (SiC) semiconductors, which have recently begun to be used as next-generation semiconductors, is 3.26 eV in the case of 4H type, and the bandgap of gallium nitride (GaN) semiconductors is 3.39 eV. is there. The shortest wavelengths of light generated by these wide bandgap semiconductors are 380 nm and 366 nm, respectively, which are ultraviolet light beyond the range of visible light.

Since these ultraviolet lights have the ability to break specific molecular bonds of the resin, it is expected that various properties will deteriorate in the long term depending on the type of resin that encloses the semiconductor chip. For example, in a light emitting element using a light emitting diode (LED) using a wide band gap semiconductor as a light source, ultraviolet light is converted into visible light by a fluorescent substance, and deterioration of the sealing resin due to unconverted ultraviolet light is prevented. Countermeasures have been devised (see, for example, Patent Document 2).

On the other hand, power semiconductor devices using wide bandgap semiconductors have been conventionally packaged by resin encapsulation without considering the correspondence to such ultraviolet light. The reason is that the first transistor to be put into practical use in SiC semiconductors and GaN semiconductors is a unipolar device such as MOSFET, so in normal operation, no forward current flows through the internal pn junction and no ultraviolet light is generated. is there.

However, even in these unipolar devices, the present inventors quickly noticed that, depending on the driving method, a forward current often flows through the parasitic pn diode inherent in the device to generate ultraviolet light. That is, a mounting structure using a sealing resin designed without paying attention to this point may deteriorate slightly faster than expected in terms of characteristics such as adhesion between the semiconductor chip and the sealing resin due to this ultraviolet light. .. Further, in a bipolar device called an IGBT made of a wide bandgap semiconductor, which is being researched for practical use in the future, ultraviolet light is generated during the original operation, so that the same problem may be faced. Further, unlike the LED mounting structure, the sealing resin is opaque in the power semiconductor mounting structure, so that ultraviolet light does not pass through and all affects the molecular binding of the sealing resin.

In view of the above problems, an object of the present invention is to provide a semiconductor device having a mounting structure capable of suppressing deterioration of the sealing resin due to light generated at a pn junction of a semiconductor chip and ensuring long-term reliability.

According to the present invention, a semiconductor chip in which a pn junction is formed, an opaque sealing resin that covers the surface of the semiconductor chip, and an opaque sealing resin that covers the surface of the semiconductor chip are arranged between the semiconductor chip and the sealing resin, and the pn junction is directed forward. The functional region includes a functional region for suppressing the light having a specific wavelength that deteriorates the sealing resin, which is generated by the flow of an electric current, from reaching the sealing resin, and the functional region includes the semiconductor chip and the sealing resin. Provided are a semiconductor device comprising an insulating functional insulating film arranged between them, wherein the functional insulating film contains a fluorescent substance that converts light having a specific wavelength into light having a long wavelength.

According to the present invention, it is possible to provide a semiconductor device having a mounting structure capable of suppressing deterioration of the sealing resin due to light generated at a pn junction of a semiconductor chip and ensuring long-term reliability.

It is a schematic cross-sectional view which shows the structure of the semiconductor device which concerns on 1st Embodiment of this invention. It is a schematic cross-sectional view which shows the other structure of the semiconductor device which concerns on 1st Embodiment of this invention. It is a schematic cross-sectional view which shows the structure of the semiconductor device which concerns on 1st modification of 1st Embodiment of this invention. It is a schematic cross-sectional view which shows the structure of the semiconductor device which concerns on 2nd modification of 1st Embodiment of this invention. It is a schematic cross-sectional view which shows the structure of the semiconductor device which concerns on 3rd modification of 1st Embodiment of this invention. It is a schematic cross-sectional view which shows the structure of the semiconductor device which concerns on 2nd Embodiment of this invention. It is a schematic cross-sectional view which shows the structure of the semiconductor device which concerns on 3rd Embodiment of this invention.

Next, an embodiment of the present invention will be described with reference to the drawings. In the description of the drawings below, the same or similar parts are designated by the same or similar reference numerals. The drawings are schematic, and the dimensions and the aspect ratio in the drawings are different from the actual ones. In addition, there are parts in which the relations and ratios of the dimensions of the drawings are different from each other.

(First Embodiment)
FIG. 1 is a schematic cross-sectional view of the semiconductor device according to the first embodiment of the present invention. In the figure, reference numeral 1 denotes a semiconductor chip, which is a wide bandgap semiconductor such as SiC or GaN in which the wavelength of light corresponding to the bandgap corresponds to ultraviolet light. In order to explain the present invention in the simplest manner, the semiconductor chip 1 is used as a vertical pn diode chip here. Of course, the present invention has the same effect on semiconductor chips such as MOSFETs, bipolar transistors, and IGBTs. The semiconductor chip 1 forms a pn junction 13 by forming a p-type semiconductor region 12 on the surface of an n-type semiconductor region 11 which is a substrate thereof. Further, there is a first main electrode 101 which is a cathode on the back surface. Further, on the surface, there is a second main electrode 102, which is an anode, connected to the p-type semiconductor region 12. The n-type semiconductor region 11 is composed of a high-concentration region that actually occupies most of the region and a low-concentration region formed in layers only in the vicinity of the p-type semiconductor region 12, but here, for convenience, no distinction is made. Illustrated.

The semiconductor chip 1 is mounted on a metal wiring formed on an insulating substrate 40. In the figure, reference numeral 41 denotes a first wiring pattern which is a cathode wiring, and the first main electrode 101 of the semiconductor chip 1 is electrically and physically connected to the first wiring pattern 41 by a bonding material 50 such as solder. It is connected. On the other hand, the second main electrode 102 is formed on the substrate 40 and is electrically connected to the second wiring pattern 42 separated from the first wiring pattern 41 by the metal wire 60. There is. The metal wire 60 is, for example, an alloy mainly composed of aluminum, and is bonded exclusively to the surface of the metal constituting the second main electrode 102 and the surface of the metal constituting the second wiring pattern 42 by an ultrasonic bonding method. ing.

The structure mounted in this way is coated with the sealing resin 30 as shown in FIG. 1 in order to deteriorate the performance of the semiconductor chip 1 due to dust from the outside and to secure the vibration resistance of the metal wire 60. Here, the sealing resin 30 is generally an epoxy resin or the like which is colored black and is opaque. Further, in FIG. 1, a functional insulating film 20 is provided between the semiconductor chip 1 and the sealing resin 30. This is a form of what is called a "functional area" in the "means for solving a problem" of the present specification. That is, when a forward current flows through the pn junction 13 in the semiconductor chip 1 made of a wide bandgap semiconductor, ultraviolet light having the ability to break the molecular bond of the organic substance constituting the sealing resin 30 is emitted (hereinafter, "" Generated light "). The functional insulating film 20, which is a kind of the above-mentioned "functional region", functions to suppress the destruction of this molecular bond.

Next, the function of the functional insulating film 20 will be described.

For example, a resin containing a fluorescent substance is used as the functional insulating film 20. Fluorescent substances are substances that have the property of converting part of their energy into heat and emitting long-wavelength light when they receive light with a short wavelength. Therefore, as the fluorescent substance contained in the functional insulating film 20, a substance that converts the ultraviolet light generated at the pn junction 13 in the semiconductor chip 1 into light harmless to the sealing resin 30, for example, visible light is selected. As such a fluorescent substance, an ultraviolet LED or a blue LED is used to realize an LED that emits red, green, or yellow, or a combination of a plurality of fluorescent substances is used to emit light of a plurality of wavelengths to realize a white LED element. It is a material used for such purposes. (See, for example, Non-Patent Document 1.).

The substrate of the functional insulating film 20 is an organic substance that is resistant to generated light and is suitable for covering the entire semiconductor chip 1 mounted on the substrate 40 as shown in FIG. Select. For example, from among aromatic polyimides, a material that can be formed with a uniform film thickness as shown in FIG. 1 by spraying or the like and is not easily sensitive to ultraviolet light emitted from the pn junction 13 is selected. Further, the ultraviolet curable resin, which undergoes a polymerization reaction by irradiation with ultraviolet light, can be used as a substrate of the functional insulating film 20 because the deterioration when the ultraviolet light is continuously irradiated after the polymerization is completed is minor as compared with other resins. .. Further, since the binding energy of the molecular bond related to silicon is generally higher than that of the carbon-based one, heat-resistant silicone or the like can also be used as the substrate of the functional insulating film 20.

Further, the film thickness of the functional insulating film 20 is set to be sufficiently thicker than the wavelength of the generated light. It is desirable to have a thickness of at least several times the wavelength.

As described above, in the semiconductor device according to the first embodiment of the present invention, light having a specific wavelength that deteriorates the sealing resin 30 is sealed between the semiconductor chip 1 and the sealing resin 30. A functional insulating film 20 that prevents the resin from reaching the resin 30 is arranged. Therefore, in the semiconductor device shown in FIG. 1, even if the semiconductor chip 1 made of a wide bandgap semiconductor, for example, emits ultraviolet light from the inside due to its operation, it is possible to prevent the sealing resin 30 from deteriorating. Deterioration is reduced. Therefore, while using a conventional resin that has a proven track record in many characteristics and is easy to use in terms of cost as the sealing resin 30, the life of the semiconductor device on which the semiconductor chip 1 made of a wide bandgap semiconductor is mounted is desired. Only that can be guaranteed.

By the way, in the semiconductor device shown in FIG. 1, an example in which the functional insulating film 20 is formed on the upper surface and the side surface of the semiconductor chip 1 having a substantially uniform thickness is shown, but the functional insulating film 20 is limited to the shape shown in FIG. I can't. For example, as shown in FIG. 2, the functional insulating film 20 may be arranged in a droplet shape as if it were potted on the upper surface of the substrate 40 (the same applies to the following modification).

<First modification>
Next, a first modification of the first embodiment of the present embodiment will be described with reference to FIG. In FIG. 3, the functional insulating film 20 includes a large number of microcrystalline particles 210 made of semiconductors having the same or narrower bandgap than the semiconductors constituting the semiconductor chip 1.

A large number of crystal defects are present inside the microcrystal particles 210, and these crystal defects form various levels in the band gap. As a result, similar to the above-mentioned fluorescent substance, when the generated light is incident on the microcrystal particles 210, light having a longer wavelength is emitted. Therefore, by containing a large number of microcrystalline particles 210 inside the functional insulating film 20, it functions in the same manner as the fluorescent substance.

As the constituent material of the microcrystal particles 210, the same material as that of the semiconductor chip 1 can be used. Alternatively, a material having a narrower bandgap, for example, an inexpensive and easily available microcrystal of Si may be used. The particle size of the microcrystal particles 210 is preferably sufficiently larger than the wavelength of the light generated from the semiconductor chip 1. Further, the density of the microcrystal particles 210 in the functional insulating film 20 is designed so that the generated light does not hit the microcrystal particles 210 and pass through the functional insulating film 20. Desirably, as shown in FIG. 3, it is preferable that several layers of microcrystalline particles 210 are formed in the functional insulating film 20.

As described above, the same effect as that described with reference to FIG. 1 can be obtained by the functional insulating film 20 containing the microcrystal particles 210. Further, according to the configuration of FIG. 3, a fluorescent substance is not essential, and microcrystal particles made of the same type of semiconductor as the semiconductor chip 1 or inexpensive microcrystal particles such as Si can be utilized. Of course, the functional insulating film 20 may contain the same fluorescent substance as in FIG.

In addition, resins generally have a larger coefficient of thermal expansion than semiconductors. Therefore, including the microcrystalline particles 210 made of a semiconductor in the sealing resin 30 relaxes the thermal stress generated between the semiconductor chip 1 and the functional insulating film 20 due to a temperature change during use. Therefore, the configuration shown in FIG. 3 is suitable from the viewpoint of suppressing damage due to thermal stress.

<Second modification>
Next, a second modification of the first embodiment of the present embodiment will be described with reference to FIG. FIG. 4 is a cross-sectional view similar to that of FIG. In FIG. 4, the functional insulating film 20 contains reflective particles 220 whose surface is at least a substance that reflects ultraviolet light from the semiconductor chip 1. Here, as in FIG. 3, the density of the reflective particles 220 in the functional insulating film 20 is shown in FIG. 4 so that the light generated from the semiconductor chip 1 does not hit the reflective particles 220 and passes through the functional insulating film 20. As described above, the reflective particles 220 are designed so that at least several layers are formed in the functional insulating film 20.

As a constituent substance of the reflective particles 220, for example, zinc oxide or titanium oxide is preferably used. However, since these substances have conductivity, the component of the insulating functional insulating film 20 is sure to intervene between the reflective particles 220.

Also here, as in the first modification, the particle size and the thickness of the reflected particles 220 are designed within a range in which the generated light does not reach the sealing resin 30. Further, the particle size of the reflected particles 220 is preferably larger than the wavelength of the generated light.

As described above, the functional insulating film 20 containing the reflective particles 220 that reflect the generated light also has the effect of preventing the generated light from reaching the sealing resin 30. The functional insulating film 20 containing the reflective particles 220 may also contain a fluorescent substance.

<Third modification example>
Next, a third modification of the first embodiment of the present embodiment will be described with reference to FIG. FIG. 5 is an enlarged cross-sectional view of a portion of the functional insulating film 20 in the vicinity of the semiconductor chip 1. The functional insulating film 20 shown in FIG. 5 contains fluorescent fine particles 230, and the fluorescent fine particles 230 are composed of a substantially spherical granular substrate 232 and a fluorescent material layer 231 that covers the surface thereof.

For the granular substrate 232, a material having a refractive index higher than that of the functional insulating film 20 is selected. As a result, as shown by the broken line arrow in FIG. 5, when the generated light L is incident on the surface of the fluorescent fine particles 230 at a shallow angle, the generated light L passes through the inside of the fluorescent material layer 231 containing the fluorescent substance many times. Also interfacially reflects and proceeds. Therefore, in the functional insulating film 20 containing the fluorescent fine particles 230, the wavelength of the generated light L is efficiently converted.

Therefore, the shape of the granular substrate 232 is preferably substantially spherical rather than having an acute-angled portion. The material of the granular substrate 232 is arbitrary as long as it is a material that absorbs the generated light L and does not significantly deteriorate. The material of the granular substrate 232 may be the same as that of the microcrystalline particles 210 and the reflective particles 220, or may be other substances. Further, the film thickness of the fluorescent substance layer 231 is preferably thicker than the wavelength of the generated light L.

Further, from the viewpoint of the coefficient of thermal expansion similar to that in FIG. 3, the material of the granular substrate 232 is a substance having a small coefficient of thermal expansion, for example, low heat that has been mixed and used in a sealing resin of a power semiconductor package. Expanded quartz glass or the like is suitable. With such a configuration, the functional region can be formed with a material that is cheaper than the microcrystalline particles 210 described with reference to FIG.

(Second embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a cross-sectional view of a semiconductor device similar to FIG. The difference is that the bonding material 50 extends from the functional insulating film 20 on the side surface of the semiconductor chip 1.

When a ZnAl material is used for the bonding material 50, when the solid ZnAl material melts, Zn vapor is generated above the melting point of the ZnAl material and adheres to the side surface of the semiconductor chip 1. As a result, the molten ZnAl material crawls up to the side surface of the semiconductor chip 1 and hardens. As a result, as shown in FIG. 6, a metal film made of the ZnAl material used for the bonding material 50 is formed on the side surface of the semiconductor chip 1, and this has a function of reflecting the generated light.

(Third Embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 7 is an enlarged cross-sectional view of FIG. 1 in the vicinity of the left side surface of the semiconductor chip 1. The sealing resin 30 and the like are omitted. The “x” mark shown in FIG. 7 is a polycrystalline region 15 formed in an inactive region adjacent to the side wall of the semiconductor chip 1. Here, the "inactive region" is a region that does not serve as a current path during operation of the semiconductor chip 1 and a region that does not affect the withstand voltage when the semiconductor chip 1 is reverse biased. Specifically, the semiconductor chip 1 It is the peripheral part of the side wall of.

The polycrystalline region 15 can be formed by using a focused pulsed laser used in a technique called laser stealth dicing. A polycrystalline region can be formed extremely locally at an arbitrary position in a semiconductor by a focused pulsed laser (see Non-Patent Document 2). The purpose of laser stealth dicing is to use this technique to form a large number of defect regions in strips so that semiconductor chips can be separated by a relatively weak external force, which is mentioned in FIG. 3 in this embodiment. Similar to the microcrystal particles 210 formed above, a crystal defect region having a function similar to that of a fluorescent substance is locally formed in the semiconductor chip 1. For this reason, by reducing the laser output and forming several layers of the area to be locally irradiated with the laser at appropriate intervals, ultraviolet light emitted from the inside of the semiconductor chip 1 can be avoided while avoiding unintentional deterioration of mechanical strength. Form a region that converts light into harmless light. If the polycrystalline region 15 is formed in the semiconductor chip 1, the functional insulating film 20 becomes unnecessary, or a part of its action can be taken over, and deterioration of the sealing resin 30 can be more easily suppressed. The effect can be realized.

(Other embodiments)
The embodiments described above with individual figures may be implemented individually or may use a plurality of techniques at the same time. Moreover, as long as it is within the scope of claims, embodiments other than those disclosed herein are also within the scope of the present invention.

Further, again, in the above description, a diode chip of a wide band gap semiconductor has been described as an example of the semiconductor chip 1, but if a pn junction is included inside and a forward current can flow there, for example, a MOSFET, a JFET, or the like. The present invention also functions effectively when applied to mounting structures of bipolar transistors, IGBTs and thyristors.

1 ... Semiconductor chip 11 ... n-type semiconductor region 12 ... p-type semiconductor region 13 ... pn junction 14 ... Depleted layer 15 ... Polycrystalline region 20 ... Functional insulating film 30 ... Encapsulating resin 40 ... Substrate 41 ... First wiring pattern 42 ... Second wiring pattern 50 ... Bonding material 60 ... Metal wire 101 ... First main electrode 102 ... Second main electrode 210 ... Microcrystalline particles 220 ... Reflective particles 230 ... Fluorescent fine particles 231 ... Fluorescent material layer 232 ... Granular substrate

Claims (4)

A semiconductor chip with a pn junction formed inside,
An opaque sealing resin that covers the surface of the semiconductor chip,
Light having a specific wavelength, which is arranged between the semiconductor chip and the sealing resin and is generated by a forward current flowing through the pn junction and deteriorates the sealing resin, reaches the sealing resin. With the functional area that suppresses
With
The functional region includes an insulating functional insulating film arranged between the semiconductor chip and the sealing resin.
The functional insulation film, light the semi conductor device you characterized by containing a fluorescent substance that converts the light of a long wavelength having a specific wavelength. A semiconductor chip with a pn junction formed inside,
An opaque sealing resin that covers the surface of the semiconductor chip,
Light having a specific wavelength, which is arranged between the semiconductor chip and the sealing resin and is generated by a forward current flowing through the pn junction and deteriorates the sealing resin, reaches the sealing resin. With the functional area that suppresses
With
The functional region includes an insulating functional insulating film arranged between the semiconductor chip and the sealing resin.
The functional insulating film contains fluorescent fine particles having a structure in which the surface of a granular substrate having a higher refractive index than the functional insulating film is coated with a fluorescent substance that converts light having the specific wavelength into light having a long wavelength. semi conductor arrangement said. The semiconductor device according to claim 2 , wherein the coefficient of thermal expansion of the granular substrate is smaller than the coefficient of thermal expansion of the substrate of the functional insulating film. A semiconductor chip with a pn junction formed inside,
An opaque sealing resin that covers the surface of the semiconductor chip,
Light having a specific wavelength, which is arranged between the semiconductor chip and the sealing resin and is generated by a forward current flowing through the pn junction and deteriorates the sealing resin, reaches the sealing resin. With the functional area that suppresses
With
The functional region includes an insulating functional insulating film arranged between the semiconductor chip and the sealing resin.
The functional insulating film, the semiconductor chip semiconductors devices you characterized in that the semiconductor and the band gap which constitutes the containing fine crystal grains consisting of the same or narrower semiconductor.

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