JP6152701B2 - Silicon carbide semiconductor device manufacturing method and silicon carbide semiconductor device - Google Patents

Description

  The present invention relates to a method for manufacturing a silicon carbide semiconductor device and a silicon carbide semiconductor device.

  A semiconductor element using silicon carbide (SiC) as a semiconductor material is expected as a next-generation semiconductor element of a semiconductor element using silicon (Si) as a semiconductor material. The reason is that the SiC semiconductor element can reduce the resistance of the element in the ON state to a hundredth compared to the Si semiconductor element, and can be used in a higher temperature environment (for example, 200 ° C. or more). This is because there are various advantages. These advantages are obtained by the characteristics of SiC itself that the band gap of SiC is about three times as large as that of Si and that the dielectric breakdown electric field strength of SiC is nearly one order of magnitude larger than that of Si.

  As SiC devices (silicon carbide semiconductor devices), Schottky barrier diodes (SBDs), planar type vertical MOSFETs (insulated gate field effect transistors), and the like have been commercialized so far. In recent years, as a method for further reducing the resistance of SiC devices, in a SBD using SiC as a semiconductor material (hereinafter referred to as SiC-SBD), a semiconductor substrate, which has conventionally been about 350 μm thick, is thinned to 150 μm or less. There has been proposed a method of reducing the thickness to the thickness (for example, see Non-Patent Document 1 below).

R. Rupp, 4 others, Performance of a 650V SiC Diode with Reduced Chip Thickness (Performance of a 650V SiC Diode Chip Thickness), Materials Science Forum Volumes 20 (17) Materials Science Forum Volumes 717-720 (2012)), (Switzerland), Trans Tech Publications, May 2012, p. 921-924

  However, as a result of extensive research by the inventor, the following has been newly found. When reducing the resistance by thinning the SiC substrate as in Non-Patent Document 1, a nickel (Ni) film is formed on the back surface of the SiC substrate after grinding, and the Ni film is silicided (chemical reaction). Thus, a Ni silicide alloy electrode to be the back electrode is formed. At this time, by making the back electrode as thin as possible, the contact resistance between the SiC substrate and the back electrode is reduced, and the amount of carbon (C) that is a by-product of silicidation of the Ni film is suppressed. The back electrode is difficult to peel off.

  However, when a damaged layer is formed on the back surface of the SiC substrate by back surface grinding, the crystallinity of the portion where the damaged layer is generated is impaired. Therefore, the silicidation of the Ni film proceeds excessively in this portion, and the back electrode The thickness becomes locally thick. As a result, there arises a problem that the contact resistance between the SiC substrate and the back electrode locally increases or the back electrode is easily peeled off. For this reason, before forming the back electrode on the back surface of the SiC substrate, it is necessary to remove the damaged layer remaining on the back surface of the SiC substrate to a thickness of about several tens of nanometers.

  Conventionally, in a Si device such as an IGBT (insulated gate bipolar transistor) using Si as a semiconductor material, a damaged layer remaining on the back surface of the Si substrate after back surface grinding is removed by chemical etching. However, since SiC is chemically stable, the damaged layer remaining on the ground surface of the SiC substrate cannot be removed by etching with a chemical solution. In Non-Patent Document 1, the back electrode is formed on the back surface of the wafer without removing the damaged layer remaining on the back surface of the wafer after the back surface grinding. However, the contact resistance between the wafer and the back electrode varies within the wafer surface. There is no mention of that the back electrode is easily peeled off.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a silicon carbide semiconductor device and a silicon carbide semiconductor device capable of reducing the resistance of an element in order to solve the above-described problems caused by the prior art. Another object of the present invention is to provide a method for manufacturing a silicon carbide semiconductor device and a silicon carbide semiconductor device capable of preventing electrode peeling in order to eliminate the above-described problems caused by the prior art.

  In order to solve the above-described problems and achieve the object, the present inventor has conducted intensive research, and as a result, gradually reduced the grain size (diameter) of the wheel abrasive grains used for grinding, and performed multiple grinding steps. After reducing the thickness of the damaged layer by performing, it was found that the remaining portion of the damaged layer is removed by dry etching or sacrificial oxidation, thereby reducing the resistance of the SiC device and preventing electrode peeling. . The present invention has been made based on such knowledge.

In order to solve the above-described problems and achieve the object of the present invention, a method for manufacturing a silicon carbide semiconductor device according to the present invention has the following characteristics. First, a grinding process is performed to grind the back surface of a semiconductor substrate made of silicon carbide to reduce the thickness of the semiconductor substrate. Next, an oxidation process is performed in which a damaged layer remaining on the back surface of the semiconductor substrate after grinding by the grinding process is oxidized, and a sacrificial oxide film is formed on the back surface of the semiconductor substrate after grinding by the grinding process. Next, a removal process for removing the sacrificial oxide film is performed. Before the oxidation step, the thickness of the damaged layer is obtained, and the thickness of the sacrificial oxide film in the oxidation step is defined based on the thickness of the damaged layer.

In order to solve the above-mentioned problems and achieve the object of the present invention, a method for manufacturing a silicon carbide semiconductor device according to the present invention has the following characteristics. First, a grinding process is performed to grind the back surface of a semiconductor substrate made of silicon carbide to reduce the thickness of the semiconductor substrate. Next, an etching process is performed in which the damaged layer remaining on the back surface of the semiconductor substrate after grinding by the grinding process is etched to reduce the thickness of the damaged layer. Next, an oxidation process is performed in which the damaged layer remaining on the back surface of the semiconductor substrate after etching by the etching process is oxidized, and a sacrificial oxide film is formed on the back surface of the semiconductor substrate after etching by the etching process. Next, a removal process for removing the sacrificial oxide film is performed. Before the etching step, the thickness of the damaged layer is obtained, and the removal amount of the back surface of the semiconductor substrate in the etching step is defined based on the thickness of the damaged layer.

  Further, in the method for manufacturing a silicon carbide semiconductor device according to the present invention, in the above-described invention, the grinding step repeats the grinding using a grindstone having a different particle diameter twice or more, and the grindstone is repeated each time the grinding is repeated. It is characterized in that the particle size of the is reduced.

  In addition, the method for manufacturing a silicon carbide semiconductor device according to the present invention has the following features in the above-described invention. Before the grinding step, a first forming step for forming a pressure-resistant structure surrounding an active region on the front surface side of the semiconductor substrate; and after the first forming step, a protective film on the front surface of the semiconductor substrate And a second forming step of forming.

Further, in the method for manufacturing a silicon carbide semiconductor device according to the present invention, in the above-described invention, in the grinding step, the thickness of the damaged layer remaining on the back surface of the semiconductor substrate after the grinding step is set in the oxidation step. The thickness is adjusted to be equal to or less than the thickness of the sacrificial oxide film.

Moreover, the manufacturing method of the silicon carbide semiconductor device according to the present invention is the above-described invention, wherein, in the grinding step, the thickness of the damaged layer remaining on the back surface of the semiconductor substrate after the grinding step is calculated in the etching step. The amount is adjusted to be equal to or less than the removal amount of the back surface of the semiconductor substrate.

  In addition, the method for manufacturing a silicon carbide semiconductor device according to the present invention is characterized in that, in the above-described invention, the thickness of the semiconductor substrate is reduced to 200 μm or less in the grinding step.

  In the method for manufacturing a silicon carbide semiconductor device according to the present invention as set forth in the invention described above, the damaged layer is a layer in which crystallinity is impaired.

  In order to solve the above-described problems and achieve the object of the present invention, a silicon carbide semiconductor device according to the present invention is manufactured by using the above-described method for manufacturing a silicon carbide semiconductor device.

  According to the above-described invention, by removing the damaged layer remaining on the back surface of the semiconductor substrate after the back surface grinding by etching, it is possible to form a back electrode having a smaller thickness and a uniform thickness than conventional ones. Since the thickness of the back electrode can be reduced, the contact resistance between the SiC substrate and the back electrode can be reduced. Also, since the thickness of the back electrode can be formed uniformly, the contact resistance is prevented from locally increasing and the amount of carbon deposited at the interface between the SiC substrate and the back electrode is suppressed. Can do.

  According to the method for manufacturing a silicon carbide semiconductor device and the silicon carbide semiconductor device according to the present invention, there is an effect that the resistance of the element can be reduced. Moreover, according to the method for manufacturing a silicon carbide semiconductor device and the silicon carbide semiconductor device according to the present invention, there is an effect that electrode peeling can be prevented.

It is sectional drawing which shows the state in the middle of manufacture of the silicon carbide semiconductor device concerning Embodiment 1. FIG. It is sectional drawing which shows the state in the middle of manufacture of the silicon carbide semiconductor device concerning Embodiment 1. FIG. It is sectional drawing which shows the state in the middle of manufacture of the silicon carbide semiconductor device concerning Embodiment 1. FIG. It is sectional drawing which shows the state in the middle of manufacture of the silicon carbide semiconductor device concerning Embodiment 1. FIG. It is sectional drawing which shows the state in the middle of manufacture of the silicon carbide semiconductor device concerning Embodiment 1. FIG. FIG. 7 is a cross sectional view showing a state in the middle of manufacture of the silicon carbide semiconductor device according to the second embodiment.

  A preferred embodiment of a method for manufacturing a silicon carbide semiconductor device and a silicon carbide semiconductor device according to the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and the accompanying drawings, it means that electrons or holes are majority carriers in layers and regions with n or p, respectively. Further, + and − attached to n and p mean that the impurity concentration is higher and lower than that of the layer or region where it is not attached. Also, in this specification, in the Miller index notation, “−” means a bar attached to the index immediately after that, and “−” is added before the index to indicate a negative index. Note that, in the following description of the embodiments and the accompanying drawings, the same reference numerals are given to the same components, and duplicate descriptions are omitted.

(Embodiment 1)
The method for manufacturing the silicon carbide semiconductor device according to the first embodiment will be described by taking as an example the case of manufacturing (manufacturing) a Schottky barrier diode (SiC-SBD) using SiC as a semiconductor material. 1 to 5 are cross-sectional views illustrating a state during the manufacture of the silicon carbide semiconductor device according to the first embodiment. First, as shown in FIG. 1, for example, an n-type 4H—SiC single crystal epitaxial substrate having a diameter of 3 inches is prepared as an n semiconductor substrate (hereinafter referred to as a SiC substrate) 1. The initial thickness (before thinning) of SiC substrate 1 may be 350 μm, for example. The front surface 2 of the SiC substrate 1 may be, for example, a (0001) surface (so-called Si surface).

  Next, a step of patterning a resist film or an oxide film formed on the front surface 2 of the SiC substrate 1 to form an ion implantation mask (not shown), and using this ion implantation mask as a mask, impurities are ionized. The step of implanting 11 is repeated to selectively form the pressure resistant structure 4 on the surface layer of the front surface 2 of the SiC substrate 1. The breakdown voltage structure 4 is a region that relaxes the electric field on the front surface 2 side of the SiC substrate 1 and maintains the breakdown voltage, and surrounds the outer periphery of the active region through which current flows in the on state. As the breakdown voltage structure 4, for example, a p-type impurity such as aluminum (Al) may be implanted to form a guard ring in the p-type region, or an n-type impurity such as phosphorus (P) may be implanted to form a p-type. An n-type region may be formed inside the region guard ring to form a double guard ring.

  Next, heat treatment is performed to activate the impurities implanted 11 into the SiC substrate 1. Next, as shown in FIG. 2, a thickness of, for example, 1.0 μm is provided on the front surface 2 of the SiC substrate 1 as a surface protective film that protects the front surface 2 of the SiC substrate 1 during back surface grinding described later. The deposited oxide film 12 is formed. Next, as shown in FIG. 3, the SiC substrate 1 is placed on, for example, a stage (not shown) with the front surface 2 facing down, and the SiC substrate 1 is ground from the back surface 3 side to obtain SiC-SBD. Grind to the position of the product thickness used as. Hereinafter, the back surface of the SiC substrate after being ground to the product thickness position is denoted by reference numeral 3a.

  Specifically, the back surface 3 of the SiC substrate 1 is first ground using a first wheel (not shown), thereby reducing the thickness of the SiC substrate 1 to, for example, about 155 μm. Then, the back surface 3 of the SiC substrate 1 is second ground using a second wheel having finer abrasive grains than the first wheel, whereby the thickness of the SiC substrate 1 is further ground by about 5 μm. As a 1st wheel, you may use the diamond wheel which consists of a grindstone of the abrasive grain in the range whose particle size (diameter) is about 5 micrometers-10 micrometers, for example. As a 2nd wheel, you may use the diamond wheel which consists of a grindstone of the abrasive grain in the range whose particle size is about 2 micrometers-about 4 micrometers, for example.

  By performing the second grinding, the thickness of the damaged layer generated on the back surface 3 of the SiC substrate 1 after the first grinding can be reduced. The damaged layer is a layer including a portion where crystallinity is impaired by grinding, for example. The loss of crystallinity means, for example, that the crystal structure is destroyed. The thickness of the damaged layer formed on the back surface 3a of the SiC substrate 1 after the first grinding can be made thinner as the grain size of the abrasive grains of the second wheel used for the second grinding becomes finer. The finer the grain size, the lower the grinding force of the second grinding, making it difficult to grind the SiC substrate 1 with high hardness. Therefore, it is preferable to improve the process efficiency (throughput) by setting the abrasive grains of the first wheel to be coarse and increasing the grinding force of the first grinding.

  You may use the wheel whose particle size of an abrasive grain is 10 micrometers or more as a 1st wheel of 1st grinding. In this case, between the first grinding and the second grinding, the grain size of the abrasive grains is finer than that of the first wheel of the first grinding and the grain size of the abrasive grains is coarser than that of the second wheel of the second grinding. It is preferable that the back surface 3 of the SiC substrate 1 is third ground using three wheels. The reason is that the damage layer generated on the back surface 3 of the SiC substrate 1 after the first grinding is reduced by the second grinding when the grain size difference between the abrasive grains of the first wheel and the abrasive grains of the second wheel is large. It will be difficult. The third grinding may be repeated a plurality of times. In that case, the grain size of the abrasive grains of the third wheel used for the third grinding is gradually reduced.

Next, as shown in FIG. 4, the _second etching of the SiC substrate 1 is performed by dry etching using capacitively coupled plasma (CCP) in a gas atmosphere 13 containing, for example, fluorocarbon (CF ₄ ) gas and oxygen (O ₂ ) gas. Etching is performed from the back surface 3a (ground surface) after grinding by a predetermined thickness (hereinafter referred to as a removal amount), and the damaged layer remaining on the back surface 3a of the SiC substrate 1 is removed after the second grinding. The amount of removal of the back surface 3a of the SiC substrate 1 is determined based on the thickness of the damaged layer obtained in advance by, for example, observing the thickness of the damaged layer remaining on the back surface 3a of the SiC substrate 1 after the second grinding. Is good.

  For example, when the thickness of the damaged layer is 0.15 μm at the maximum, the removal amount of the back surface 3a of the SiC substrate 1 by etching can substantially remove the damaged layer remaining on the back surface 3a of the SiC substrate 1 after the second grinding. It should be about 0.2 μm. In addition, the amount of removal of the back surface 3a of the SiC substrate 1 by etching can be increased by performing etching for a long time of, for example, 30 minutes or more, but considering the process efficiency, for example, about 0.2 μm or more and 0.5 μm or less. Is desirable. For this reason, after the second grinding, the damaged layer remaining on the back surface 3a of the SiC substrate 1 can be removed almost completely by etching with the removal amount within the above range. It is better to adjust the thickness of the remaining damaged layer.

  Next, as shown in FIG. 5, after the deposited oxide film 12 is removed, an interlayer insulating film 5 is formed on the front surface 2 of the SiC substrate 1 so that the active region is exposed. Next, a Ni film is deposited on the back surface 3a and the front surface 2 of the SiC substrate 1 to a thickness of, for example, 0.02 μm. Thereafter, the Ni film on the back surface 3a and the front surface 2 of the SiC substrate 1 is silicidized by heat treatment to form a Ni silicide alloy electrode that becomes the front surface electrode 6 and the back surface electrode 7, respectively. The front surface electrode 6 is an anode electrode (Schottky electrode), and is in contact with the front surface 2 and the breakdown voltage structure 4 of the SiC substrate 1 in the active region. The end of the front electrode 6 may extend on the interlayer insulating film 5. Back electrode 7 is a cathode electrode (ohmic electrode) and contacts the entire back surface 3 a of SiC substrate 1. In this way, the silicon carbide semiconductor device according to the first embodiment is completed.

  According to the method for manufacturing the silicon carbide semiconductor device according to the first embodiment described above, SiC-SBD (hereinafter referred to as Example 1) is manufactured under the above-described various conditions, and the back electrode 7 of Example 1 is observed by cross-sectional observation. The thickness was verified. That is, the back surface grinding of the SiC substrate 1 includes the first grinding using the first wheel of abrasive grains having a particle size in the range of about 5 μm to 10 μm and the first grinding of abrasive grains in the range of about 2 μm to 4 μm. Second grinding using two wheels was performed. After the second grinding, a damaged layer remains at a maximum thickness of 0.15 μm on the back surface 3 a of the SiC substrate 1. Therefore, the SiC substrate 1 is dry-etched by a thickness (removed amount) of 0.2 μm from the back surface 3 a of the SiC substrate 1. The damage layer remaining on the back surface 3a of 1 was removed. As a result, in Example 1, it was confirmed that the back electrode 7 can be uniformly formed with a thickness of 0.04 μm.

  On the other hand, as a comparison, a SiC-SBD (hereinafter referred to as a comparative example) in which the damaged layer remaining on the back surface of the SiC substrate after the second grinding was not removed was produced. And the cross-sectional observation verified the thickness of the back surface electrode of the comparative example similarly to Example 1. The manufacturing method of the comparative example is the same as that of Example 1 except that the damaged layer remaining on the back surface of the SiC substrate after the second grinding is not removed. In the comparative example, it was confirmed that the thickness of the back electrode locally increased by about 0.2 μm. Moreover, as a result of comparing the cross-sectional images of Example 1 and the comparative example, Example 1 is separated from the back surface 3a of the SiC substrate 1 along with the silicidation of the Ni film, as compared with the comparative example. It was confirmed that the amount of carbon deposited at the interface between the back surface 3a and the back electrode 7 can be reduced to about 1/5 times.

  As described above, according to the first embodiment, the damaged electrode remaining on the back surface of the SiC substrate after the back surface grinding is removed by etching, so that the back surface electrode having a smaller thickness and a uniform thickness than the conventional one. Can be formed. Specifically, the thickness of the back electrode can be reduced to about 0.01 μm or less. Since the thickness of the back electrode can be reduced, the contact resistance between the SiC substrate and the back electrode can be reduced. Thereby, the resistance of the element can be reduced. Also, since the thickness of the back electrode can be formed uniformly, the contact resistance is prevented from locally increasing and the amount of carbon deposited at the interface between the SiC substrate and the back electrode is suppressed. Can do. Thereby, the contact resistance between the SiC substrate and the back electrode in the wafer surface can be prevented from varying, the element resistance can be stably reduced, and the back electrode can be prevented from peeling off.

(Embodiment 2)
Next, the method for manufacturing the silicon carbide semiconductor device according to the second embodiment will be described by taking a case of producing SiC-SBD as an example. FIG. 6 is a cross-sectional view showing a state during the manufacture of the silicon carbide semiconductor device according to the second embodiment. The manufacturing method of the silicon carbide semiconductor device according to the second embodiment is different from the manufacturing method of the silicon carbide semiconductor device according to the first embodiment in that the damaged layer remaining on the back surface 3a of the SiC substrate 1 after the second grinding is sacrificed. It is a point to remove.

  Specifically, first, as in the first embodiment, the SiC substrate 1 is prepared, and the steps from the formation of the pressure-resistant structure 4 to the second grinding are sequentially performed (see FIGS. 1 to 3). Next, as shown in FIG. 6, the damaged layer remaining on the back surface 3 a of the SiC substrate 1 after the second grinding is oxidized by dry oxidation (thermal oxidation) at a temperature of about 1000 ° C. for 15 minutes, for example. A thermal oxide film 21 having a thickness of 0.4 μm, for example, is formed on the back surface 3a. Next, the deposited oxide film 12 and the thermal oxide film 21 are removed by buffered hydrofluoric acid (BHF) (sacrificial oxidation). Thereby, the damaged layer remaining on the back surface 3a of SiC substrate 1 after the second grinding can be removed. Thereafter, in the same manner as in the first embodiment, by forming interlayer insulating film 5, back electrode 7 and front surface electrode 6, the silicon carbide semiconductor device according to the second embodiment is completed (see FIG. 5).

  In the thermal oxidation for forming the thermal oxide film 21, since the deposited oxide film 12 has already been formed on the front surface 2 of the SiC substrate 1, the oxidation rate of the front surface 2 of the SiC substrate 1 ( The oxidation rate is smaller than the oxidation rate of the back surface 3a. Thereby, it is possible to prevent the breakdown voltage structure 4 already formed on the front surface 2 side of the SiC substrate 1 from being oxidized and broken, and to suppress the deterioration of breakdown voltage characteristics. The breakdown of the pressure-resistant structure 4 means, for example, that the guard ring constituting the pressure-resistant structure 4 becomes thin or the guard ring disappears.

  The thickness of the thermal oxide film 21 is preferably determined based on the thickness of the damaged layer obtained in advance by, for example, observing the thickness of the damaged layer remaining on the back surface 3a of the SiC substrate 1 after the second grinding. . For example, when the damage layer has a maximum thickness of 0.15 μm, the thickness of the thermal oxide film 21 is, for example, about 0.4 μm that can oxidize the damage layer remaining on the back surface 3a of the SiC substrate 1 after the second grinding. There should be. Although the thickness of the thermal oxide film 21 can be increased by thermal oxidation for a long time, for example, 0.4 μm or more and 1.0 μm or less in consideration of the possibility that the pressure-resistant structure 4 may be destroyed by thermal oxidation and the process efficiency. It is desirable to set the degree. Therefore, the damaged layer remaining on the back surface 3a of the SiC substrate 1 after the second grinding so that the damaged layer remaining on the back surface 3a of the SiC substrate 1 after the second grinding can be almost completely oxidized with a thickness within the above range. It is better to adjust the thickness.

  In accordance with the method for manufacturing the silicon carbide semiconductor device according to the second embodiment described above, SiC-SBD (hereinafter referred to as Example 2) is manufactured under the above-described various conditions, and the back electrode 7 of Example 2 is observed by cross-sectional observation. The thickness was verified. That is, the back surface grinding conditions of the SiC substrate 1 in the second embodiment are the same as those in the first embodiment. After the second grinding, the damaged layer remained at a maximum thickness of 0.15 μm on the back surface 3 a of the SiC substrate 1. Therefore, the damaged layer was removed by sacrificial oxidation using the thermal oxide film 21 having a thickness of 0.4 μm. As a result, it was confirmed that the back electrode 7 can be uniformly formed with a thickness of 0.04 μm in Example 2 as in Example 1. In addition, as a result of comparing the cross-sectional images of Example 2 and the above comparative example, in Example 2 as well as in Example 1, carbon deposited on the interface between the back surface 3a of the SiC substrate 1 and the back electrode 7 was obtained. It was confirmed that the amount of precipitation can be reduced.

  As described above, according to the second embodiment, the same effect as in the first embodiment can be obtained by removing the damaged layer remaining on the back surface of the SiC substrate after the back surface grinding by sacrificial oxidation. Further, according to the second embodiment, before the thermal oxide film is formed on the back surface of the SiC substrate, the front surface of the SiC substrate is protected by the deposited oxide film, so that the main surface of the SiC substrate is The oxidation rate of the front surface can be made smaller than the oxidation rate of the back surface of the SiC substrate. Thereby, it is possible to suppress the breakdown structure from being destroyed by thermal oxidation.

(Embodiment 3)
Next, the method for manufacturing the silicon carbide semiconductor device according to the third embodiment will be described by taking as an example the case of producing SiC-SBD. The silicon carbide semiconductor device manufacturing method according to the third embodiment is different from the silicon carbide semiconductor device manufacturing method according to the second embodiment in that the damaged layer remaining on the back surface 3a of the SiC substrate 1 is etched and sacrificed after the second grinding. It is a point to remove in combination with oxidation.

  Specifically, first, as in the first embodiment, the SiC substrate 1 is prepared, and the steps from the formation of the pressure-resistant structure 4 to the second grinding are sequentially performed (see FIGS. 1 to 3). Next, as in the first embodiment, the back surface 3a (ground surface) after the second grinding of the SiC substrate 1 is, for example, 0.1 μm thick (removed) by dry etching using capacitively coupled plasma in a gas atmosphere 13, for example. The damage layer remaining on the back surface 3a of the SiC substrate 1 after the second grinding is reduced (see FIG. 4).

  Next, as in the second embodiment, the damaged layer remaining on the back surface 3a of the SiC substrate 1 after dry etching is oxidized by dry oxidation at a temperature of about 1000 ° C. for 10 minutes, for example, and is applied to the back surface 3a of the SiC substrate 1 For example, a thermal oxide film 21 having a thickness of 0.2 μm is formed (see FIG. 6). Next, similarly to the second embodiment, the deposited oxide film 12 and the thermal oxide film 21 are removed (sacrificial oxidation). Thereby, the damaged layer remaining on back surface 3a of SiC substrate 1 after dry etching can be removed. Thereafter, in the same manner as in the first embodiment, by forming interlayer insulating film 5, back electrode 7 and front surface electrode 6, the silicon carbide semiconductor device according to the third embodiment is completed (see FIG. 5).

  The amount of removal of the back surface 3a of the SiC substrate 1 by etching and the amount of removal of the back surface 3a of the SiC substrate 1 by sacrificial oxidation (the thickness of the thermal oxide film 21) are the damages remaining on the back surface 3a of the SiC substrate 1 after the second grinding. The thickness of the layer is preferably acquired in advance by, for example, cross-sectional observation, and is determined based on the acquired thickness of the damaged layer. In order to suppress the breakdown of the pressure-resistant structure due to thermal oxidation, it is preferable to increase the removal amount of back surface 3a of SiC substrate 1 by etching rather than the removal amount of back surface 3a of SiC substrate 1 by sacrificial oxidation. For example, when the thickness of the damaged layer is 0.15 μm at the maximum, the damaged layer is removed to a thickness of 0.1 μm by dry etching, for example, and the damaged layer remaining on the back surface 3 of the SiC substrate 1 after the dry etching is sacrificed. Remove with.

  In accordance with the method for manufacturing the silicon carbide semiconductor device according to the third embodiment described above, SiC-SBD (hereinafter referred to as Example 3) is manufactured under the above-described various conditions, and the back electrode 7 of Example 3 is observed by cross-sectional observation. The thickness was verified. That is, the back surface grinding conditions of the SiC substrate 1 in Example 3 are the same as those in Example 1. After the second grinding, a damaged layer remains at a maximum thickness of 0.15 μm on the back surface 3 a of the SiC substrate 1. Therefore, dry etching is performed from the back surface 3 a of the SiC substrate 1 by a thickness (removal amount) of 0.1 μm to 0.2 μm. The damaged layer was removed by sacrificial oxidation by the thermal oxide film 21 having a thickness of. As a result, it was confirmed that the back electrode 7 can be uniformly formed with a thickness of 0.04 μm in Example 3 as in Examples 1 and 2. Further, as a result of comparing the cross-sectional images of Example 3 and the above comparative example, Example 3 also precipitates at the interface between back surface 3a and back electrode 7 of SiC substrate 1 in the same degree as Examples 1 and 2. It was confirmed that the amount of carbon deposited can be reduced.

  As described above, according to the third embodiment, the same effects as those of the first and second embodiments are obtained by removing the damaged layer remaining on the back surface of the SiC substrate after the back surface grinding by a combination of etching and sacrificial oxidation. Can be obtained. Further, according to the third embodiment, the thickness of the thermal oxide film for sacrificial oxidation can be reduced as compared with the case where the damaged layer remaining on the back surface of the SiC substrate after the back surface grinding is removed only by sacrificial oxidation. Therefore, it is possible to suppress the breakdown structure from collapsing due to thermal oxidation.

  As described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in each embodiment, the case where a SiC-SBD is manufactured is described as an example. For example, a SiC (metal-oxide-semiconductor) type semiconductor device using SiC as a semiconductor material may be used. Applicable to devices. In each embodiment, the (0001) plane of the SiC substrate is used as the front surface, and the (000-1) plane (so-called C plane) serving as the back surface is ground. Has confirmed that a damage layer having the same thickness is formed on both the (0001) plane and the (000-1) plane, and the present invention can also be applied to the case where the (000-1) plane is the front plane. It is.

  In the first and third embodiments, the case where the damaged layer remaining on the back surface of the SiC substrate after the back surface grinding is removed by dry etching is described as an example. However, the present invention is not limited to this. For example, wet etching is used instead of dry etching. May be used. In the second and third embodiments, when the damaged layer remaining on the back surface of the SiC substrate after the back surface grinding is removed by sacrificial oxidation, a thermal oxide film is formed on the back surface of the SiC substrate by dry oxidation. Alternatively, a thermal oxide film may be formed by wet oxidation. Further, the protective film for protecting the front surface of the SiC substrate is not limited to the deposited oxide film, and may be, for example, a resist film. In addition, the present invention has been described by taking an example in which silicon carbide is used as a semiconductor material. However, the present invention is not limited thereto, and other materials having a band gap larger than Si are used as a semiconductor material. The present invention is also applicable when used as a semiconductor material. Further, the present invention is similarly established even when the conductivity type is reversed.

  As described above, the method for manufacturing a silicon carbide semiconductor device and the silicon carbide semiconductor device according to the present invention are useful for a silicon carbide semiconductor device in which a semiconductor substrate is thinned to reduce resistance by grinding.

DESCRIPTION OF SYMBOLS 1 SiC substrate 2 SiC substrate front surface 3 SiC substrate back surface 3a Product thickness position of SiC substrate 4 Withstand voltage structure 5 Interlayer insulating film 6 Front surface electrode 7 Back electrode 11 Ion implantation 12 Deposited oxide film 13 Gas Atmosphere 21 Thermal oxide film

Claims (8)

Grinding the back surface of the semiconductor substrate made of silicon carbide, and reducing the thickness of the semiconductor substrate;
Oxidizing the damaged layer remaining on the back surface of the semiconductor substrate after grinding by the grinding step, and forming a sacrificial oxide film on the back surface of the semiconductor substrate after grinding by the grinding step;
A removal step of removing the sacrificial oxide film;
Only including,
Prior to the oxidation step, the thickness of the damaged layer is obtained, and the thickness of the sacrificial oxide film in the oxidation step is defined based on the thickness of the damaged layer. Manufacturing method. Grinding the back surface of the semiconductor substrate made of silicon carbide, and reducing the thickness of the semiconductor substrate;
Etching the damaged layer remaining on the back surface of the semiconductor substrate after grinding by the grinding step, and reducing the thickness of the damaged layer;
Oxidizing the damaged layer remaining on the back surface of the semiconductor substrate after etching by the etching step, and forming a sacrificial oxide film on the back surface of the semiconductor substrate after etching by the etching step;
A removal step of removing the sacrificial oxide film;
Only including,
Before the etching step, the thickness of the damaged layer is obtained, and the removal amount of the back surface of the semiconductor substrate in the etching step is defined based on the thickness of the damaged layer Device manufacturing method. The thickness of the damaged layer remaining on the back surface of the semiconductor substrate after the grinding step is adjusted to be equal to or less than the thickness of the sacrificial oxide film in the oxidation step in the grinding step. A method for manufacturing a silicon carbide semiconductor device. The said grinding process adjusts the thickness of the said damage layer which remains on the back surface of the said semiconductor substrate after the said grinding process below to the removal amount of the back surface of the said semiconductor substrate in the said etching process. The manufacturing method of the silicon carbide semiconductor device of description. 5. The grinding process according to claim 1, wherein the grinding using a grindstone having a different particle diameter is repeated twice or more, and the grindstone diameter is reduced each time the grinding is repeated. A method for manufacturing a silicon carbide semiconductor device according to claim 1. Before the grinding process,
A first forming step of forming a breakdown voltage structure surrounding an active region on the front surface side of the semiconductor substrate;
A second forming step of forming a protective film on the front surface of the semiconductor substrate after the first forming step;
The method for manufacturing a silicon carbide semiconductor device according to claim 1, further comprising:   The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein in the grinding step, the thickness of the semiconductor substrate is reduced to 200 μm or less.   The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the damaged layer is a layer in which crystallinity is impaired.

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