Semiconductor device and method for manufacturing semiconductor device

Abstract

This semiconductor device (1) comprises: a semiconductor substrate (2) on which a semiconductor element is formed; a surface electrode (5) that is formed on a first main surface of the semiconductor substrate (2); a rear surface electrode (6) that is formed on a second main surface of the semiconductor substrate (2); and a surface protection film (7) that is formed on the first main surface of the semiconductor substrate (2) so as to cover the surface electrode (5), and has an opening that exposes a portion of the surface electrode (5). The upper surface of the surface protection film (7) is roughened by cutting marks.

Description

Semiconductor device and method for manufacturing the same

[0001] The present disclosure relates to a semiconductor device and a method for manufacturing the semiconductor device.

[0002] There is known a semiconductor device having a surface protection film made of a polyimide resin or the like formed on its surface. For example, Patent Document 1 listed below discloses a technique for making the top surface of the surface protection film uneven (hereinafter referred to as "roughening") by sputtering.

[0003] Japanese Patent Application Laid-Open No. 2007-158113

[0004] When a semiconductor device having a surface protective film is mounted in a resin molded package, if the adhesion between the surface protective film and the molded resin cannot be ensured, the molded resin will peel off from the surface protective film due to stress caused by heat generated during operation of the semiconductor device, thereby reducing the reliability of the semiconductor device. Although roughening the top surface of the surface protective film can be expected to improve the adhesion between the surface protective film and the molded resin, even if the surface is roughened by sputtering as in Patent Document 1, the maximum surface roughness of the top surface of the surface protective film is small, ranging from a few nanometers to a few tens of nanometers, and the adhesion between the surface protective film and the molded resin cannot be sufficiently increased.

[0005] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a semiconductor device that can improve adhesion between a surface protection film and a molding resin.

[0006] The semiconductor device according to the present disclosure comprises a semiconductor substrate on which a semiconductor element is formed, a surface electrode formed on a first main surface of the semiconductor substrate, a back electrode formed on a second main surface of the semiconductor substrate, and a surface protective film formed on the first main surface of the semiconductor substrate so as to cover the surface electrode and having an opening exposing a portion of the surface electrode, wherein the upper surface of the surface protective film is roughened by cutting marks.

[0007] According to the present disclosure, the maximum surface roughness of the upper surface of the surface protection film can be increased, so that when the semiconductor device is sealed with a molding resin, the adhesion between the surface protection film and the molding resin can be increased, which contributes to improving the reliability of the semiconductor device.

[0008] The objects, features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description and the accompanying drawings.

[0009] Fig. 1 is a cross-sectional view showing the configuration of a semiconductor device according to a first embodiment. Fig. 2 is a cross-sectional view showing the configuration of a semiconductor device according to a second embodiment. Fig. 3 is a process diagram showing a method for manufacturing a semiconductor device according to a third embodiment. Fig. 4 is a process diagram showing a method for manufacturing a semiconductor device according to a third embodiment. Fig. 5 is a process diagram showing a method for manufacturing a semiconductor device according to a third embodiment. Fig. 6 is a process diagram showing a method for manufacturing a semiconductor device according to a third embodiment. Fig. 7 is a process diagram showing a method for manufacturing a semiconductor device according to a third embodiment.

[0010] First Preferred Embodiment FIG. 1 is a cross-sectional view showing the configuration of a semiconductor device 1 according to a first preferred embodiment.

[0011] The semiconductor device 1 includes a semiconductor substrate 2 on which a semiconductor element is formed. Here, the upper surface of the semiconductor substrate 2 in FIG. 1 is defined as a "first main surface" and the lower surface thereof is defined as a "second main surface."

[0012] The material of the semiconductor substrate 2 may be silicon (Si) or a wide bandgap semiconductor such as silicon carbide (SiC) or gallium nitride (GaN). When a wide bandgap semiconductor is used as the material of the semiconductor substrate 2, superior characteristics can be obtained in operation at high voltages, large currents, and high temperatures compared to semiconductor devices using silicon. There are no restrictions on the type of semiconductor element formed on the semiconductor substrate 2. When the semiconductor device 1 is a semiconductor device for power control, power elements such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), IGBTs (Insulated Gate Bipolar Transistors), SBDs (Schottky Barrier Diodes), and PNDs (PN Junction Diodes) are formed on the semiconductor substrate 2.

[0013] In this embodiment, an example is shown in which a PN junction diode, which is a vertical power element, is formed on a semiconductor substrate 2. In this case, as shown in Fig. 1, a P-type anode region 3 is formed in a surface layer portion on the first main surface side of an N-type semiconductor substrate 2, and an N-type region below the anode region 3 becomes a cathode region 4. The anode region 3 contains a high concentration of P-type impurities (e.g., boron (B)), and the cathode region 4 contains a high concentration of N-type impurities (e.g., phosphorus (P)).

[0014] A front surface electrode 5 serving as an anode electrode is formed on a first main surface of the semiconductor substrate 2, and a back surface electrode 6 serving as a cathode electrode is formed on a second main surface of the semiconductor substrate 2. A surface protective film 7 made of a thermosetting resin such as polyimide is formed on the first main surface of the semiconductor substrate 2 so as to cover the front surface electrode 5. An opening is formed in the surface protective film 7 to expose a portion of the front surface electrode 5, and wiring or the like can be connected to the front surface electrode 5 through this opening.

[0015] 1, the semiconductor device 1 is sealed with a mold resin 8. The mold resin 8 is made of a material such as an epoxy resin or a polyimide resin.

[0016] Here, the upper surface of the surface protective film 7 is cut using a cutting machine, and is roughened by the cutting marks. Roughening by cutting can increase the roughness of the upper surface of the surface protective film 7 compared to the roughening by sputtering disclosed in the above-mentioned Patent Document 1. In this embodiment, the maximum surface roughness of the upper surface of the surface protective film 7 is adjusted to 100 nm or more. A surface protective film 7 with such a large maximum surface roughness on the upper surface can achieve high adhesion with the mold resin 8 due to the anchor effect.

[0017] As will be described in detail later, in conventional semiconductor devices, a protective film equivalent to the surface protective film 7 is provided to protect the surface (first main surface) of the semiconductor substrate 2 when processing the back surface (second main surface) of the semiconductor substrate, and is removed when the product is shipped.

[0018] According to the semiconductor device 1 of embodiment 1, high adhesion is obtained between the mold resin 8 and the surface protective film 7, so that the mold resin 8 is prevented from peeling off from the surface protective film 7 due to stress caused by heat generation in the semiconductor device 1, thereby improving the reliability of the semiconductor device.

[0019] The above-described effect is particularly effective when the semiconductor substrate 2 is a wide bandgap semiconductor, since it is expected that the semiconductor device 1 will operate at high temperatures. Furthermore, the thermal stress that occurs when the semiconductor substrate 2 is made of silicon carbide is much greater than when the semiconductor substrate 2 is made of silicon, which is a common semiconductor material, so the above-described effect is very effective when the semiconductor substrate 2 is made of silicon carbide.

[0020] 2 is a cross-sectional view showing the configuration of a semiconductor device 1 according to a second embodiment. As shown in Fig. 2, in the second embodiment, the surface protective film 7 is made up of a first protective film 7a and a second protective film 7b. The other configurations are the same as those in the first embodiment (Fig. 1).

[0021] The first protective film 7a is an upper layer of the surface protective film 7, and its upper surface is roughened by cutting marks. The second protective film 7b is a lower layer of the surface protective film 7, and is interposed between the first protective film 7a and the semiconductor substrate 2. The first protective film 7a and the second protective film 7b are made of a thermosetting resin such as polyimide. However, the materials of the first protective film 7a and the second protective film 7b are selected so that the thermal expansion coefficient of the second protective film 7b is a value between the thermal expansion coefficients of the first protective film 7a and the semiconductor substrate 2. Because the thermal expansion coefficients of silicon and silicon carbide, which are materials for the semiconductor substrate 2, are smaller than those of polyimide, for example, the thermal expansion coefficient of the first protective film 7a is set to 80 ppm / K, and the thermal expansion coefficient of the second protective film 7b is set to 50 ppm / K, for example.

[0022] If the thermal expansion coefficient of the surface protective film 7 differs greatly from that of the semiconductor substrate 2, stress caused by heat generation in the semiconductor device 1 may cause cracks or peeling at the interface between the surface protective film 7 and the semiconductor substrate 2. In this embodiment, the second protective film 7b, which has a thermal expansion coefficient relatively close to that of the semiconductor substrate 2, is interposed in the portion where the surface protective film 7 contacts the semiconductor substrate 2, thereby reducing the stress generated between the surface protective film 7 and the semiconductor substrate 2.

[0023] Third Preferred Embodiment In a third preferred embodiment, a method for manufacturing the semiconductor device 1 shown in the first and second preferred embodiments will be described. Figures 3 to 8 are process diagrams for explaining the manufacturing method.

[0024] First, a semiconductor element such as a PN junction diode (not shown in FIGS. 3 to 8) is formed on the semiconductor substrate 2 , and a surface electrode 5 is formed on the first main surface of the semiconductor substrate 2 .

[0025] 3, a surface protective film 7 that covers the surface electrodes 5 is formed on the first main surface of the semiconductor substrate 2. When forming the semiconductor device 1 according to the second embodiment, the surface protective film 7 has a two-layer structure made up of a first protective film 7a and a second protective film 7b.

[0026] Then, the upper surface of the surface protective film 7 is cut by a cutting machine, and large irregularities (irregularities corresponding to the shape of the surface electrode 5) on the upper surface of the surface protective film 7 are flattened, while the cutting marks roughen the upper surface of the surface protective film 7, as shown in Fig. 4. After this cutting process, a heat treatment may be performed to harden the surface protective film.

[0027] Next, as shown in FIG. 5 , with the first main surface of the semiconductor substrate 2 covered with the surface protective film 7, the semiconductor substrate 2 is turned over and the second main surface of the semiconductor substrate 2 is processed. In this process, for example, the second main surface is ground to thin the semiconductor substrate 2, and impurities are implanted into the second main surface. Furthermore, as shown in FIG. 6 , with the first main surface of the semiconductor substrate 2 covered with the surface protective film 7, a back electrode 6 is formed on the second main surface of the semiconductor substrate 2. In this manner, the second main surface side of the semiconductor substrate 2 is processed with the first main surface covered with the surface protective film 7. Therefore, the surface protective film 7 also serves to protect the structure on the first main surface side of the semiconductor substrate 2 when the second main surface side of the semiconductor substrate 2 is processed.

[0028] 7, the semiconductor substrate 2 is turned over again and a portion of the surface protective film 7 is removed to form an opening in the surface protective film 7 that exposes a portion of the surface electrode 5. Then, as shown in FIG. 8, the semiconductor substrate 2 is cut into pieces to form chips of the semiconductor device 1.

[0029] Finally, the semiconductor device 1 is sealed with a molding resin 8, thereby obtaining the configuration of the semiconductor device 1 shown in FIG. 1 or FIG.

[0030] In the manufacturing method of semiconductor device 1 according to this embodiment, surface protective film 7 serves as a protective film that protects the structure on the first main surface side of semiconductor substrate 2 when processing the second main surface side of semiconductor substrate 2. As mentioned above, in conventional semiconductor devices, a protective film equivalent to surface protective film 7 is removed before product shipment. However, in this embodiment, surface protective film 7 remains in semiconductor device 1 after commercialization, thereby reducing the number of processes and thereby reducing costs. Furthermore, by processing the top surface of surface protective film 7 by cutting using a cutting machine, it is possible to adjust the maximum surface roughness of the top surface of surface protective film 7 without adding an additional process.

[0031] It is possible to freely combine the embodiments, and to modify or omit the embodiments as appropriate.

[0032] The above description is illustrative in all respects, and it is understood that countless variations not illustrated can be envisioned.

[0033] REFERENCE SIGNS LIST 1 semiconductor device, 2 semiconductor substrate, 3 anode region, 4 cathode region, 5 front surface electrode, 6 rear surface electrode, 7 front surface protective film, 7a first protective film, 7b second protective film, 8 molding resin

Claims

1. A semiconductor substrate on which a semiconductor element is formed; a surface electrode formed on a first main surface of the semiconductor substrate; a back surface electrode formed on a second main surface of the semiconductor substrate; a surface protection film formed on the first main surface of the semiconductor substrate so as to cover the surface electrode and having an opening exposing a portion of the surface electrode; Equipped with The upper surface of the surface protection film is roughened by cutting marks. Semiconductor device.

2. The maximum surface roughness of the upper surface of the surface protection film is 100 nm or more. The semiconductor device according to claim 1 .

3. The surface protective film is a thermosetting resin.

3. The semiconductor device according to claim 1 or 2.

4. the surface protective film includes a first protective film having an upper surface roughened by the cutting trace, and a second protective film interposed between the first protective film and the semiconductor substrate, The thermal expansion coefficient of the second protective film is a value between the thermal expansion coefficient of the first protective film and the thermal expansion coefficient of the semiconductor substrate.

3. The semiconductor device according to claim 1 or 2.

5. The semiconductor substrate is a wide band gap semiconductor.

3. The semiconductor device according to claim 1 or 2.

6. forming a semiconductor element on a semiconductor substrate; forming a surface electrode on a first main surface of the semiconductor substrate; forming a surface protection film on the first main surface of the semiconductor substrate to cover the surface electrodes; cutting an upper surface of the surface protection film and roughening the upper surface of the surface protection film by a cutting mark; forming a back surface electrode on a second main surface of the semiconductor substrate while the first main surface of the semiconductor substrate is covered with the surface protection film; forming an opening in the surface protective film after forming the back surface electrode, the opening exposing a portion of the front surface electrode; forming semiconductor device chips by cutting the semiconductor substrate; A method for manufacturing a semiconductor device comprising the steps of: