JP2013105761A - Manufacturing method of power semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a power semiconductor device capable of improving an isolation voltage and reliability under a high-temperature environment.SOLUTION: By combining an oxygen plasma surface treatment step (step 5) and a preliminary heating process (step 6) before silicone gel injection, adhesiveness between a silicone gel 9 (a protective material), and an insulating substrate 1 having a conductive pattern and a semiconductor chip 2 is improved, thus an isolation voltage and reliability of a power semiconductor device under a high-temperature environment can be improved.

Description

  The present invention relates to a method for manufacturing a power semiconductor device, and more particularly to a method for manufacturing a power semiconductor device in which silicone gel or the like is enclosed.

  In a power semiconductor device such as a power semiconductor module, silicone is contained in the resin case to protect the conductive pattern of the insulating substrate with the conductive pattern disposed in the resin case and the power semiconductor chip bonded to the conductive pattern with solder or the like. Fill with gel and seal. The silicone gel ensures the insulation performance (insulation breakdown voltage) in the resin case.

  FIG. 11 is a schematic manufacturing process diagram of a conventional power semiconductor device. This process diagram shows a schematic process until the silicone gel is injected. Detailed description of each step is shown in FIGS.

  12 to 16 are cross-sectional views of the main part manufacturing process showing the manufacturing method of the conventional power semiconductor device in the order of processes. Here, the power semiconductor device is a power semiconductor module that houses a power semiconductor chip such as an IGBT or a power MOSFET.

  First, in FIG. 12 (process 1), the power semiconductor chip 2 is joined on the insulating substrate 1 with the conductive pattern, and the power semiconductor chip 2 and the conductive pattern (not shown) of the insulating substrate 1 with the conductive pattern are connected by the bonding wire 3. The insulating substrate with conductive pattern 1 is obtained by bonding a conductive pattern to be a circuit wiring pattern on an insulating substrate such as ceramic (not shown) and bonding a back surface conductive layer on the back surface. This conductive pattern is usually formed of copper foil or the like.

Next, in FIG. 13 (process 2), the back surface conductive layer (not shown) of the insulating substrate 1 with the conductive pattern is joined to the heat dissipation base 4 with solder or the like.
Next, in FIG. 14 (step 3), the bottom of the resin case 5 is fixed to the side surface of the heat dissipation base 4 with an adhesive. The adhesive is an epoxy resin adhesive, and the bonding conditions are a temperature of about 150 ° C. and a processing time of about 3 minutes.

Next, in FIG. 15 (step 4), the power semiconductor chip 2 and the conductive pattern are connected to the external lead-out terminal 6 fixed to the resin case 5 by the bonding wire 3 or the like.
Next, in FIG. 16 (step 5), the silicone gel 9 is injected into the resin case 5.

  Further, in Patent Document 1, electrical connection is made between a semiconductor element and a lead in a state where at least a part of the outer surface of the semiconductor element and the lead is covered with polyimide, and then the leaded semiconductor element is sealed with a sealing resin. A semiconductor device to be stopped is a manufacturing method, and at least a polyimide portion is subjected to plasma treatment prior to resin sealing of the leaded semiconductor element.

  By this plasma treatment, the polyimide surface in contact with the sealing resin is modified and the compatibility with the resin is improved. Therefore, it is described that according to this method, it is possible to obtain a semiconductor device which is excellent in moisture resistance adhesion between the polyimide and the sealing resin at the interface and hardly causes package cracks in the solder reflow process.

  In Patent Document 2, a semiconductor element is mounted on a substrate 31 and formed on a nickel film on a copper electrode in a method of manufacturing an electronic component in which the semiconductor element and an electrode of the substrate are connected by wire bonding. On the surface of the gold film, bonding obstructions generated by the heat treatment at the time of bonding the semiconductor element are removed by the first plasma treatment with argon gas to improve the wire bonding property. Thereafter, the surface of the resist whose adhesion to the resin mold is reduced by the first plasma treatment is modified by the second plasma treatment using oxygen gas plasma to improve the adhesion of the sealing resin to the resin mold. It is described.

JP-A-5-152362 JP-A-11-145120

In the conventional process of FIG. 11 and the conventional manufacturing method of FIGS.
(1) As the insulation resistance characteristics of the power semiconductor device, the dielectric breakdown voltage (insulation breakdown voltage) decreases in a high temperature environment (for example, 150 ° C. atmosphere) as compared with a normal temperature environment as shown in FIG.
(2) Normally, since the power semiconductor device is used in a high temperature state due to the heat generated by the power semiconductor chip 2, a decrease in the withstand voltage at a high temperature causes a decrease in reliability.

These are phenomena that occur because the adhesion between the insulating substrate with a conductive pattern 1 and the power semiconductor chip 2 and the silicone gel 9 is lowered.
In order to prevent this, there is a method of performing surface treatment with O ₂ plasma as described in Patent Documents 1 and 2 above.

  However, the plasma surface treatments disclosed in Patent Documents 1 and 2 are insufficient for power semiconductor devices such as power semiconductor modules used in a high temperature environment, resulting in a decrease in dielectric breakdown voltage and a decrease in dielectric strength. There is a concern about the decline in reliability.

FIG. 17 is a diagram showing the relationship between the conventional IGBT module temperature and the breakdown voltage.
When the dielectric breakdown voltage at normal temperature is 7.0 kV to 8.0 kV, the voltage drops to 5.0 kV to 6.0 kV at a high temperature of 150 ° C.

  In Patent Documents 1 and 2, the IC is a target semiconductor device, and the applied voltage is as low as several tens of volts. On the other hand, a power semiconductor device is as high as several thousand volts, and is more likely to cause dielectric breakdown than an IC.

  Moreover, in the said patent documents 1, 2, the object which plasma-treats is an epoxy resin, and the description which made the silicone gel object is not made. Further, there is no description about preheating after the plasma surface treatment and before covering the surface with a protective material.

  In a power semiconductor device, when an especially large resin case 5 is used, if an epoxy resin is used instead of a silicone gel, the epoxy resin has poor flexibility and a large thermal stress, so that the resin case or the insulating substrate with a conductive pattern is used. It cannot be used because it cracks or breaks.

  Moreover, in the said patent document 2, although the improvement of the adhesiveness of the resist of a board | substrate and resin mold is described, about the adhesiveness of an insulating substrate with a conductive pattern (ceramic board | substrate and circuit wiring pattern) and a silicone gel. Is not listed.

  In addition, although the above-mentioned patent document describes that the adhesion is improved in order to prevent damage due to external force and intrusion of foreign matter, the dielectric breakdown voltage of the semiconductor device is improved as in the present invention. There is no mention of that.

  An object of the present invention is to provide a method of manufacturing a power semiconductor device that can solve the above-described problems and improve the dielectric strength and reliability in a high temperature environment.

  In order to achieve the above object, according to the first aspect of the present invention, an insulating substrate with a conductive pattern bonded on a heat dissipation base and a semiconductor bonded on the insulating substrate with a conductive pattern are provided. In a method for manufacturing a power semiconductor device, comprising: a chip; a resin case that houses the insulating substrate with the conductive pattern and the semiconductor chip; and is bonded to the heat dissipation base; and a protective material filled in the resin case. A step of bonding a semiconductor chip on the insulating substrate, a step of bonding the insulating substrate with the conductive pattern to the heat radiating base, a step of bonding a resin case to the heat radiating base, a surface of the insulating substrate with the heat radiating pattern, and the Performing oxygen plasma surface treatment on the surface of the semiconductor chip, heating the insulating substrate with a heat radiation pattern and the semiconductor chip at a high temperature, Removing the, the manufacturing method characterized by comprising the step of filling the protective material in the resin case, the.

According to the invention described in claim 2, the plasma power is 200W to 600W and the plasma processing time is 30 seconds in the oxygen plasma surface treatment condition. It is preferable that the flow rate of oxygen (O ₂ ) is 30 ml / min to 100 ml / min.

  Further, according to the invention described in claim 3 of the claims, in the invention described in claim 1, the conditions for the high temperature heating are as follows: the temperature is 100 ° C. or more and 200 ° C. or less, and the heating time is 30 minutes. It is good that it is 2 hours or less.

According to the invention described in claim 4 of the claims, in the invention described in claim 1, the protective material may be a silicone gel or an epoxy resin.
According to the invention described in claim 5, the material of the insulating substrate constituting the insulating substrate with conductive pattern in the invention described in claim 1 is Al ₂ O ₃ , Si ₃ N. ₄ or AlN, and the material of the conductive pattern is preferably copper.

  The oxygen plasma surface treatment in the present invention refers to cleaning or hydrophilizing the surface to be treated with ions or active species in plasma generated using an oxidizing gas such as oxygen.

  In this invention, by combining the oxygen plasma surface treatment step and the preheating step before the silicone gel injection, the adhesion between the silicone gel (protective material), the insulating substrate with the conductive pattern, and the semiconductor chip is improved, under a high temperature environment. Thus, it is possible to improve the withstand voltage and reliability of the power semiconductor device.

It is a manufacturing process figure of the power semiconductor device of 1st Example of this invention. It is principal part manufacturing process sectional drawing of the power semiconductor device of 1st Example of this invention. FIG. 3 is a cross-sectional view showing the main part manufacturing process of the power semiconductor device according to the first embodiment of the invention, following FIG. 2; FIG. 4 is a cross-sectional view showing the main part manufacturing process of the power semiconductor device according to the first embodiment of the invention, following FIG. 3; FIG. 5 is a cross-sectional view of the essential part manufacturing process of the power semiconductor device according to the first embodiment of the invention, following FIG. 4. FIG. 6 is a cross-sectional view of the essential part manufacturing process of the power semiconductor device according to the first embodiment of the invention, following FIG. 5. FIG. 7 is a cross-sectional view of the essential part manufacturing process of the power semiconductor device according to the first embodiment of the invention, following FIG. 6; FIG. 8 is a cross-sectional view of the main part manufacturing process of the power semiconductor device according to the first embodiment of the invention, following FIG. 7. It is a figure which shows the relationship between oxygen plasma processing conditions and withstand voltage. It is a figure which shows the relationship between IGBT module temperature and a dielectric breakdown voltage when the manufacturing method of this invention is applied. It is a schematic manufacturing-process figure of the conventional power semiconductor device. It is principal part manufacturing process sectional drawing of the conventional power semiconductor device. FIG. 13 is a main-portion manufacturing process cross-sectional view of the conventional power semiconductor device, following FIG. 12; FIG. 14 is a main-portion manufacturing process cross-sectional view of the conventional power semiconductor device, following FIG. 13; FIG. 15 is a main-portion manufacturing process cross-sectional view of the conventional power semiconductor device, following FIG. 14; FIG. 16 is a main-portion manufacturing process cross-sectional view of the conventional power semiconductor device, following FIG. 15; It is a figure which shows the relationship between the conventional IGBT module temperature and a dielectric breakdown voltage. It is a figure which shows the suitable range of oxygen plasma surface treatment conditions.

Embodiments will be described in the following examples. The same reference numerals are assigned to the same parts as in the prior art.
<Example 1>
FIG. 1 is a manufacturing process diagram of a power semiconductor device according to a first embodiment of the present invention. This process diagram shows the process until the silicone gel is injected. Detailed description of each step is shown in FIGS.

  2 to 8 are cross-sectional views of the main part manufacturing process showing the method of manufacturing the power semiconductor device according to the first embodiment of the present invention in the order of processes. Here, the power semiconductor device is a power semiconductor module that houses a power semiconductor chip such as an IGBT or a power MOSFET.

  First, in FIG. 2 (process 1), the power semiconductor chip 2 is joined on the insulating substrate 1 with the conductive pattern, and the conductive pattern (not shown) of the power semiconductor chip 2 and the insulating substrate 1 with the conductive pattern is connected to the connecting conductor such as the bonding wire 3. Connect with. Although not shown, the insulating substrate with a conductive pattern 1 is formed by bonding a conductive pattern serving as a circuit wiring pattern on an insulating substrate such as ceramic and bonding a back conductive layer on the back surface. This conductive pattern is usually formed of copper foil or the like.

Next, in FIG. 3 (process 2), the back surface conductive layer (not shown) of the insulating substrate 1 with the conductive pattern is joined to the heat radiating base 4 with solder (not shown).
Next, in FIG. 4 (step 3), the bottom of the resin case 5 is fixed to the side surface of the heat dissipation base 4 with an adhesive. The adhesive is an epoxy resin adhesive, and the bonding conditions are a processing temperature of about 150 ° C. and a processing time of about 3 minutes.

  Next, in FIG. 5 (step 4), the power semiconductor chip 2 and the conductive pattern are connected to the external lead-out terminal 6 fixed to the resin case 5 with a connection conductor such as the bonding wire 3.

Next, in FIG. 6 (step 5), oxygen plasma surface treatment is performed on the surface of the insulating substrate with conductive pattern 1 and the surface of the power semiconductor chip 2 in the plasma processing apparatus 50. As described above, the conductive pattern of the insulating substrate with a conductive pattern 1 is a copper foil, and the material of the insulating substrate is ceramic such as Al ₂ O ₃ , Si ₃ N ₄ , AlN.

  Next, in FIG. 7 (step 6), the preheating conditions for preheating before injecting the silicone gel 9 are as follows. The heating temperature is about 150 ° C. and the heating time is about 1 hour. This preheating is performed using a thermostat 8 or a hot plate.

Next, in FIG. 8 (step 7), the silicone gel 9 is injected into the resin case 5.
In FIG. 6 (step 5), the size of the parallel plate electrode 7 for generating oxygen plasma provided in the plasma processing apparatus 50 is, for example, L (vertical) × W (horizontal) = about 250 mm × It is about 150 mm. The interelectrode distance D is, for example, about 50 mm to 100 mm. The oscillation frequency f of plasma generation is 13.56 MHz. The flow rate Q of oxygen (O ₂ ) 10 introduced into the plasma processing apparatus is preferably about 50 ml / min. The flow rate Q is preferably 30 ml or more and 100 ml or less. If the flow rate Q exceeds 100 ml, the film quality of the plasma oxide film is changed and the dielectric strength is reduced. On the other hand, if it is less than 30 ml, the plasma oxide film is too thin, the adhesion is lowered, and the withstand voltage is lowered. As the oxidizing gas used for the plasma treatment, nitrous oxide (N ₂ O) or the like may be used in addition to oxygen.

In addition, the results of experiments on the oxygen plasma processing conditions and the withstand voltage in FIG. 6 (step 5) will be described.
FIG. 9 is a diagram showing the relationship between oxygen plasma treatment conditions and withstand voltage. In the figure, ◯ indicates that the withstand voltage is improved, Δ indicates no change in withstand voltage, and x indicates a decrease in withstand voltage.

  As oxygen plasma surface treatment conditions, the plasma power P is 200 W to 600 W, and the plasma treatment time t is 30 seconds to 700 seconds. If the plasma power P or the plasma processing time t exceeds this range, the thermal oxide film grows and the film quality is changed from the plasma oxide film. Therefore, the adhesiveness is lowered and the insulation resistance is lowered. On the other hand, when the thickness is smaller than this range, the thickness of the plasma oxide film is reduced, the adhesion is also lowered, and the dielectric strength is lowered. Further, it is more preferable that the plasma power P is 250 W to 600 W and the plasma processing time t is 30 seconds to 600 seconds from the viewpoint of improving the dielectric strength.

  Further, as can be seen from FIG. 9, in the preferable oxygen plasma surface treatment conditions, the relationship between the plasma power P and the plasma treatment time t has an inversely proportional relationship. FIG. 18 shows this relationship, and the shaded area indicates the range of preferable conditions. Accordingly, when the plasma power P is increased within the range of FIGS. 9 and 18, the dielectric strength can be improved by reducing the plasma processing time t. Although the reason why the dielectric strength is improved is unknown, the adhesion of the silicone gel 9 is improved when the thickness of the plasma oxide film is several nm or more under the above conditions.

  In this embodiment, after the oxygen plasma surface treatment in the above step 5 is performed, the preheating in the above step 6 is performed so that the insulating substrate 1 with the conductive pattern and the power semiconductor chip 2 on the other side to which the silicone gel 9 is in close contact. The surface is dried and moisture is removed. Therefore, compared with the case where it does not preheat, the adhesiveness of the silicone gel 9, and the insulated substrate 1 with a conductive pattern, and the power semiconductor chip 2 can be improved.

  In FIG. 7 (Step 6), as preheating conditions, the heating temperature is preferably 100 ° C. or more and 200 ° C. or less, and the heating time is 30 minutes or more and 2 hours or less. Outside this range, problems such as oxidation and insufficient moisture removal occur.

  As described above, the combination of the oxygen plasma surface treatment step and the preheating step before injecting the silicone gel allows the adhesion between the silicone gel 9 and the insulating substrate 1 with the conductive pattern, the silicone gel 9 and the power semiconductor chip 1. The adhesion between the two can be improved.

By improving the adhesion, a reduction in the withstand voltage of the power semiconductor device under a high temperature environment (for example, about 150 ° C.) can be prevented, and the reliability of the power semiconductor device can be improved.
FIG. 10 is a diagram showing the relationship between the IGBT module temperature and the dielectric breakdown voltage when the manufacturing method of the present invention is applied.

  When the breakdown voltage at room temperature is about 7.0 kV to 8.0 kV, the breakdown voltage is about 7.0 kV to 9.5 kV at a high temperature of 150 ° C. When the breakdown voltage at a high temperature in the conventional manufacturing method is compared with the breakdown voltage at a high temperature of the present invention, the breakdown voltage at a high temperature of the IGBT module to which the manufacturing method of the present invention is surely applied is high.

  That is, in this embodiment, in the method of manufacturing a semiconductor device, by combining an oxygen plasma surface treatment step and a preheating step before silicone gel injection, a silicone gel (protective material), an insulating substrate with a conductive pattern, and a semiconductor chip Therefore, the withstand voltage of the power semiconductor device can be improved.

  In addition, the said process 6 demonstrated the case where it put just before the said process 7. FIG. This is because it is preferable to put it immediately before the step 7 because the standing time until the step 7 is shortened. However, even if the process is not performed immediately before the process 7 but is performed between the process 2 and the process 7, the breakdown voltage is improved.

  Although the silicone gel 9 has been described as a protective material for ensuring the insulating performance of the power semiconductor device, the protective material is not limited to this as long as the protective material has high insulation and elasticity. Moreover, when the resin case of the power semiconductor device is relatively small, an epoxy resin may be used.

  In particular, in a power semiconductor device manufactured from SiC or GaN, the size of the resin case 5 is relatively small, and an epoxy resin is used as a protective material for high-temperature operation. In this case, the same effect can be obtained by using the manufacturing method of the present invention.

DESCRIPTION OF SYMBOLS 1 Insulation board | substrate with a conductive pattern 2 Power semiconductor chip 3 Bonding wire 4 Radiation base 5 Resin case 6 External lead-out terminal 7 Electrode 8 Thermostatic bath 9 Silicone gel 10 Oxygen

Claims (5)

Insulating substrate with conductive pattern bonded on heat dissipation base, semiconductor chip bonded on insulating substrate with conductive pattern, and resin case containing said insulating substrate with conductive pattern and said semiconductor chip and bonded to said heat dissipation base And a manufacturing method of a power semiconductor device comprising a protective material filled in the resin case,
Bonding a semiconductor chip on an insulating substrate with a conductive pattern;
Bonding the insulating substrate with a conductive pattern to a heat dissipation base;
Bonding a resin case to the heat dissipation base;
Performing oxygen plasma surface treatment on the surface of the insulating substrate with a heat radiation pattern and the surface of the semiconductor chip;
Heating the insulating substrate with a heat radiation pattern and the semiconductor chip at a high temperature to remove moisture;
Filling the resin case with a protective material;
The manufacturing method of the power semiconductor device characterized by the above-mentioned. In the oxygen plasma surface treatment conditions, the plasma power is 200 W to 600 W, the plasma treatment time is 30 seconds to 700 seconds, and the flow rate of oxygen (O ₂ ) is 30 ml / min to 100 ml / min. A method for manufacturing a power semiconductor device according to claim 1.   2. The method of manufacturing a power semiconductor device according to claim 1, wherein the high-temperature heating conditions are a temperature of 100 ° C. to 200 ° C. and a heating time of 30 minutes to 2 hours.   The method for manufacturing a power semiconductor device according to claim 1, wherein the protective material is silicone gel or epoxy resin. _2. The power semiconductor according to claim 1, wherein a material of an insulating substrate constituting the insulating substrate with a conductive pattern is Al ₂ O ₃ , Si ₃ N ₄ or AlN, and a material of the conductive pattern is copper. Device manufacturing method.