METHOD FOR MANUFACTURING A SEMICONDUCTOR DEVICE AND SEMICONDUCTOR DEVICE

Abstract

A method for fabricating a semiconductor device is provided, enabling the reduction of the width of a termination region and the suppression of the electric field concentration in that region. The method is for a semiconductor device that has a termination region at the periphery of the active region. In this termination region, a first semiconductor region of a first electrically conductive type has formed a second semiconductor region on its surface, which is a plurality of well regions of a second electrically conductive type. The method is characterized by forming the second semiconductor region by injecting impurities of the second electrically conductive type using a mask. This mask is used to form the second semiconductor region, such that an interval S(x) is substantially equal to the value given by S(x) = S max - (S max- S min ) × (x / XN) 1 / 2 is defined where x is the distance from the reference window at the outermost periphery and the interval S(x) is the interval between the injection window at a position at distance x and an injection window on the side of the active area thereof.

Description

Technical area

[0001] The present invention relates to a method for manufacturing a semiconductor device and a semiconductor device. State of the art

[0002] In recent years, price competition in the field of power semiconductor devices has intensified, and there is a need for cost reduction. To reduce costs, it is necessary to increase the diameter of a wafer, lower the process temperature, and reduce the size of a chip. This requires shallowing the junction in a termination region, reducing the width of the termination region, and suppressing the electric field concentration in the termination region.

[0003] Patent Literature 1 discloses, as a structure of a termination region, for example, a termination structure (32) provided on an outer peripheral portion of a semiconductor element. The termination region (32) includes an N-type drift region (1) formed in a semiconductor substrate (30) and a P-type impurity region (2) formed on an upper surface portion in the N-type drift region (1). When macroscopically observed, a P-type impurity concentration of the P-type impurity region (2) decreases from an inner peripheral portion to an outer peripheral portion of the termination structure (32), and when microscopically observed, the P-type impurity region (2) is formed by a plurality of P-type high-concentration regions (2b) and low-concentration regions (2a) surrounding them, with some portions where the low-concentration regions (2a) are separated from each other (abstract, Fig. 2).

[0004] Furthermore, Patent Literature 1 discloses that an aperture ratio of an injection mask (20) used in ion injection to form such a P-type impurity region (2) is reduced toward the outside of the termination structure (32) (paragraph 0042), and discloses that, although examples of a function for reducing the aperture ratio include a linear function and the like, a function having a high reduction rate such as an exponential function is desirable, and that, for example, by using an exponential function that is downwardly convex or a function that decreases according to a polynomial when viewed macroscopically, a local concentration of the electric field can be reduced (paragraph 0043). Citation listPatent literature

[0005] Patent literature 1: WO 2014 / 054 319 A1 Summary of the inventionTechnical problem

[0006] However, Patent Literature 1 discloses, as the function for reducing the aperture ratio of the injection mask (20), the linear function, the exponential function (a x ), which is downwardly convex, or the function that decreases according to the polynomial. However, as a result of simulations conducted by the inventors of the present application, it was found that the shape of the mask for reducing the width of the termination region and suppressing the electric field concentration in the termination region is desirably a different shape from that specified by the functions disclosed in Patent Literature 1.

[0007] An object of the present invention is to provide a method for manufacturing a semiconductor device and a semiconductor device with which it is possible to realize a reduction in the width of a termination region and a suppression of the electric field concentration in the termination region. Solution to the problem

[0008] In order to achieve the above-described object, a method for manufacturing a semiconductor device of the present invention is, for example, a method for manufacturing a semiconductor device having, in a periphery of an active region, a termination region in which second semiconductor regions, which are a plurality of well regions having a second conductivity type, are formed in a front surface of a first semiconductor region having a first conductivity type, the second semiconductor regions being formed by injecting impurities of the second conductivity type using a mask as a mask for forming the second semiconductor regions in which a distance S(x) between an injection window at a position of a distance x and the nearest injection window on a side of the active region is substantially equal to a value given by S(x)=Smax−(Smax−Smin)×(x / XN)1 / 2 wherein, among the second semiconductor regions in which a depletion layer extending into the first semiconductor region is continuous with the active region in a thermal equilibrium state, the injection window corresponding to the second semiconductor region formed at a position farthest from the active region is defined as a reference window, a position of the reference window on one side of the active region is defined as X0, a distance between a position of the injection window adjacent to the active region on one side of the active region and X0 is defined as XN, a distance between the reference window and the nearest injection window on one side of the active region is defined as Smax,a distance between an end portion of the active region and the injection window adjacent to the active region is defined as Smin and a distance from XO is defined as x.,

[0009] In addition, a semiconductor device of the present invention is, for example, a semiconductor device having an active region and a termination region formed in a periphery of the active region, wherein the second semiconductor region formed using the method described above is included in the termination region. Advantageous effects of the invention

[0010] According to the present invention, it is possible to realize a method for manufacturing a semiconductor device and a semiconductor device with which it is possible to realize a reduction in the width of a termination region and a suppression of the electric field concentration in the termination region. Short description of the drawings Fig. 1 shows a cross-sectional view of a semiconductor device of Example 1. Fig. 2 is a plan view illustrating a shape of a mask of Example 1. Fig. 3 is a diagram illustrating a distance between one injection window and the next injection window on one side of an active area in the mask of Example 1 and a width of the injection window. Fig. Figure 4 shows a diagram illustrating a dosage profile of Example 1. Fig. Figure 5 shows a diagram illustrating a dosage profile of Example 2. Fig. 6 is a diagram illustrating a distance between one injection window and the next injection window on one side of an active area in a mask of Example 3 and a width of the injection window. Fig. 7 is a diagram illustrating a distance between one injection window and the next injection window on one side of an active area in a mask of Example 4 and a width of the injection window. Fig. Fig. 8 is a diagram illustrating the effect of the present invention. Fig. Fig. 9 is a diagram illustrating the effect of the present invention. Description of embodiments

[0011] Examples of the present invention will be described below with reference to the drawings. In each drawing and example, the same or similar components are denoted by the same reference numerals, and overlapping descriptions are omitted. Example 1

[0012] Fig. 1 shows a cross-sectional view of a semiconductor device of Example 1.

[0013] A semiconductor device 10 of Example 1 includes a termination region 12 in a periphery of an active region 11, in which second semiconductor regions 2, which are a plurality of well regions having a second conductivity type (for example, a p-type), are formed in a front surface of a first semiconductor region 1 having a first conductivity type (for example, an n-type). Here, it is described that the first conductivity type is n-type and the second conductivity type is p-type, but the first conductivity type may be p-type and the second conductivity type may be n-type.

[0014] A semiconductor element such as an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field-effect transistor (MOSFET), a diode, or the like is formed in the active region 11, but is not shown in the drawing. A semiconductor substrate on which the semiconductor device 10 is formed may be made of Si, SiC, or the like, but the present invention is not limited thereto.

[0015] The first semiconductor region 1 and the second semiconductor region 2 are also formed in the active region 11, and the second semiconductor region 2 in the active region 11 is referred to herein as a second semiconductor region 2a.

[0016] In addition, the semiconductor device 10 includes an oxide film 4 formed to cover the first semiconductor region 1 or the second semiconductor region 2, an electrode 5 formed in the active region 11, and a channel stopper 6 formed in the termination region and having a high concentration of a first conductivity type. The electrode 5 is, for example, a gate electrode or an emitter electrode in the case of an IGBT, a gate electrode or a source electrode in the case of a MOSFET, or an anode electrode in the case of a diode. Fig. 1, only a front surface of the semiconductor device 10 is shown, and a back surface is not shown. On the back surface of the semiconductor device 10, an electrode (not shown) is provided, for example, a collector electrode in the case of an IGBT, a drain electrode in the case of a MOSFET, or a cathode electrode in the case of a diode.

[0017] In the semiconductor device 10 of Example 1, in a thermal equilibrium state, a depletion layer 3 extending into the first semiconductor region 1 is continuous from the active region 11 to each of the second semiconductor regions 2, and each of the second semiconductor regions 2 is essentially an intrinsic region. One of the characteristics is that depletion (shrinkage of the intrinsic region) of each of the second semiconductor regions 2 starts from an outer peripheral side (a side away from the active region 11) due to the application of a voltage from the second semiconductor region 2.

[0018] Of the second semiconductor regions 2 in the termination region 12, a plurality of second semiconductor regions 2 overlap each other on a side closer to the active region 11 to form a well region that is also continuous with the second semiconductor region 2a in the active region 11. Of the second semiconductor regions 2 in the termination region 12, the second semiconductor regions 2 form well regions that are separated from each other on a side remote from the active region 11.

[0019] Here, among the second semiconductor regions 2 in which the depletion layer 3 extending into the first semiconductor region 1 is continuous with the active region 11 in a thermal equilibrium state, the second semiconductor region 2 formed at a position farthest from the active region 11 is referred to as the outermost second semiconductor region 2b in which the depletion layer 3 is continuous.

[0020] Fig. 2 is a plan view illustrating a shape of a mask of Example 1. Fig. Figure 3 shows a diagram illustrating a distance between one injection window and the next injection window on one side of an active area in the mask of Example 1 and a width of the injection window. In Fig. 3, a horizontal axis indicates a position POS, a vertical axis on the left side indicates a distance S (corresponding to a width of a blocking portion 21) between an injection window 22 of a mask 20 and the nearest injection window 22 on one side of the active area 11, and a vertical axis on the right side indicates a width W of the injection window 22.

[0021] Impurities of a second conductivity type are determined using the Fig. 2 to form the second semiconductor regions 2. The mask 20 includes the blocking portion 21 for blocking the impurities and the injection window 22, which is an opening for allowing the impurities to pass through. Due to the diffusion of the injected impurities, the size of the second semiconductor region 2 becomes larger than the size of the injection window 22.

[0022] Here, among the injection windows 22, the injection window 22 corresponding to the second semiconductor region 2a of the active region 11 is referred to as an active region injection window 22a, and the injection window 22 corresponding to the outermost second semiconductor region 2b in which the depletion layer 3 is continuous is referred to as a reference window 22b.

[0023] The shape of the mask 20 in Example 1 is such that a distance S(x) between the injection window 22 at a position of a distance x and the nearest injection window 22 on one side of the active region 11 is substantially equal to a value specified by the following equation (1), where a position of the reference window 22b on one side of the active region 11 is defined as X0, a distance between a position of the injection window 22 adjacent to the active region 11 on one side of the active region 11 and X0 is defined as XN, a distance between the reference window 22b and the nearest injection window 22 on one side of the active region 11 is defined as Smax, a distance between an end portion of the active region 11 and the injection window 22 adjacent to the active region 11 is defined as Smin, and a distance from X0 is defined as x. S(x)=Smax−(Smax−Smin)×(x / XN)1 / 2

[0024] As a result, it is possible to reduce the width of the termination region in the termination region 12 and suppress the electric field concentration in the termination region. Details of the effects are described below.

[0025] In addition, the shape of the mask 20 in Example 1 is such that a width W(x) of the injection window 22 at a position of the distance x decreases with increasing distance from the active region 11.

[0026] In this case, the width of the second semiconductor region 2 can be made smaller than in a case where the width W(x) of the injection window 22 is constant regardless of the position of the pitch x and therefore the width of the termination region 12 can be reduced.

[0027] In Example 1, as in Fig. 3, the width W(x) of the injection window at the position of distance x is made to decrease linearly with increasing distance from the active region 11.

[0028] Fig. Figure 4 shows a diagram illustrating a dosage profile of Example 1. In Fig. 4 a horizontal axis indicates a position POS and a vertical axis indicates a dosage amount DO.

[0029] In Example 1, when the impurities of the second conductivity type are injected using the mask 20, the dosage profile is such that a dosage amount in the second semiconductor region 2a of the active region 11 is substantially equal to a dosage amount in the second semiconductor region 2 of the termination region 12.

[0030] As a result, it is possible to form the second semiconductor region 2 by injecting the impurities of the second conductivity type using a single mask 20.

[0031] Next, the effect of realizing the reduction in the width of the termination region 12 and the suppression of the electric field concentration in the termination region 12 due to the shape of the mask 20 of Example 1 will be described in detail.

[0032] Fig. Figure 8 shows a diagram illustrating the effect of the present invention. In Fig. 8, a horizontal axis indicates a position POS and a vertical axis indicates a distance S (corresponding to a width of the blocking portion 21) between the injection window 22 of the mask 20 and the next injection window 22 on one side of the active area 11.

[0033] It is assumed that the distance S(x) between the injection window 22 at the position of the distance x from X0 and the nearest injection window 22 on one side of the active area 11 can be expressed by the following equation (2). S(x)=Smax−(Smax−Smin)×(x / Lx)α

[0034] In the case of α = 1 / 2, this equation becomes equal to equation (1). Here, assuming that the number of injection windows 22 is 15 and the distance between the position of the injection window 22 adjacent to the active region 11 on one side of the active region 11 and X0 is Lx(α), the distance S(x) and Lx(1 / 4), Lx(1 / 2), Lx(1,0) and Lx(2,0) are calculated for α = 1 / 4, 1 / 2, 1,0 and 2,0, respectively, and Fig. 8 shown.

[0035] As a result, it is found that the smaller α is, the smaller Lx(α) is, that is, the width of the termination region 12 can be made smaller.

[0036] Here, α = 1.0 corresponds to the distance S(x) that increases linearly toward the outer periphery of the termination region 12 (as x approaches 0), which is not strictly the same as, but approximately corresponds to, the case in Patent Literature 1 where the aperture ratio of the injection mask (20) decreases toward the outside of the termination structure (32) according to a linear function. In addition, α = 2.0 approximately corresponds to the case in Patent Literature 1 where the aperture ratio of the injection mask (20) decreases toward the outside of the termination structure (32) according to the polynomial. However, in the case of α = 1.0 or α = 2.0, Lx(1.0) or Lx(2.0) becomes larger than Lx(1 / 2), and it is found that this case is not suitable for reducing the width of the termination region 12.

[0037] Although in Fig. 8, calculations are also carried out for a case in which the distance S(x) depends on e xas an example of an exponential function (which is approximately the case where the aperture ratio of the injection mask (20) decreases according to an exponential function toward the outside of the termination structure (32) in Patent Literature 1), and the results are approximately close to the case of α = 2.0. Therefore, it is determined that this case is also not suitable for reducing the width of the termination region 12.

[0038] When a withstand voltage is examined, it is about 900 V for all of α = 1 / 4, 1 / 2, 1.0 and 2.0, which is a sufficient withstand voltage for use as a 750 V withstand voltage device.

[0039] Fig. Figure 9 shows a diagram illustrating the effect of the present invention. In Fig. 9 indicates a horizontal axis α and a vertical axis indicates the maximum electric field strength Emax (kV / cm) in the termination region 12 when 750 V is applied.

[0040] As in Fig. As shown in Figure 9, it is found that in the case of α = 1 / 2, the maximum electric field strength Emax is the smallest. The fact that the maximum electric field strength Emax is small means that the electric field concentration in the termination region 12 can be suppressed.

[0041] An avalanche breakdown is a phenomenon that occurs when electrons accelerated by an electric field collide with an atom, causing the electrons to be pulled away from the atom in an avalanche-like manner. When the electric field strength at which the breakdown occurs is Ec and the electric field strength is E, a current I suddenly increases as shown by the following equation (3). I=I0 / [1−(E / Ec)k] where I0 and k are constants. Furthermore, since the avalanche breakdown occurs when the electric field strength E reaches the breakdown-occurring electric field strength Ec, E < Ec.

[0042] From equation (3), it can be seen that the smaller the electric field strength E, the larger the denominator of equation (3) becomes and the smaller the current I becomes. As a result, the avalanche breakdown is less likely to occur, and the smaller current is beneficial to ensure long-term reliability when a voltage is applied for a long period of time. As shown in Fig. 9, it is found that in the case of α = 1 / 2, the maximum electric field strength Emax is the smallest and therefore the electric field strength E and current I also become small, which is the most suitable.

[0043] Out of Fig. 8 and Fig. 9, it is found that the case of α = 1 / 2 in equation (2), i.e., equation (1), is the most suitable.

[0044] As described above, according to Example 1, by using the mask 20 having a shape in which the distance S(x) between the injection window 22 at the position of the distance x and the nearest injection window 22 on one side of the active region 11 is substantially equal to the value specified by Equation (1), it is possible to realize a reduction in the width of the termination region 12 and a suppression of the electric field concentration in the termination region 12. Example 2

[0045] Fig. Figure 5 shows a diagram illustrating a dosage profile of Example 2. Fig. 5 shows a diagram that Fig. 4 of Example 1.

[0046] Example 2 differs from Example 1 in the dosage profile.

[0047] The dosage profile of Example 2 is as in Fig. 5 shows a dosage profile in which the dosage amount of the second semiconductor region 2 in the termination region 12a on a side closer to the active region 11 in the termination region 12 is greater than the dosage amount of the second semiconductor region 2 in the termination region 12b on a side further away from the active region 11 in the termination region 12.

[0048] As a result, there is the effect of suppressing a decrease in the dielectric strength due to positive interfacial charges.

[0049] However, in Example 2, in order to change the dosage amount depending on the area, it is necessary to inject the impurities of a second conductivity type using two masks 20, and thus Example 2 also differs from Example 1 in this point.

[0050] Unlike the above, this example is the same as Example 1, and thus the overlapping description is omitted. Example 3

[0051] Fig. 6 is a diagram illustrating a distance between one injection window and the next injection window on one side of an active area in a mask of Example 3 and a width of the injection window. Fig. 6 shows a diagram that Fig. 3 of Example 1.

[0052] Example 3 differs from Example 1 by the width W(x) of the injection window 22 at the position of the distance x. N

[0053] The shape of the mask 20 in Example 3 is such that a width W(x) of the injection window 22 at a position of the distance x decreases linearly with increasing distance from the active region 11, and an inclination of a decrease on a side closer to the active region 11 (x > XN') is greater than an inclination of a decrease on a side farther from the active region 11 (x ≤ XN'). In Fig. 6, Wmax' is a value of the width W(x) of the injection window 22 at a position where the distance x is XN'.

[0054] Next, the reason for changing the slope of the decrease in the width W(x) of the injection window 22 will be explained. By heat treatment after injecting the second conductivity type impurities, the width of the second semiconductor region 2 is increased, and the peak concentration is also reduced. The amount of decrease in the peak concentration is increased when the width W(x) of the injection window 22 is smaller, and decreased when the width W(x) is larger. In contrast, the width of the injection window 22 in the second semiconductor region 2a in the active region 11 is extremely larger than the width W(x) of the injection window in the termination region 12, and thus the decrease in the peak concentration in the second semiconductor region 2a in the active region 11 is smaller than in the case of the second semiconductor region 2 in the termination region 12.Therefore, a difference in peak concentration occurs between the active region 11 and the second semiconductor region 2 adjacent thereto. Here, in a case where there is a large difference in concentration, there is a concern that an electric field concentration may occur at the end of the active region 11, resulting in a decrease in withstand voltage. For this reason, it is preferable that the width W(x) of the injection window 22 be larger near the active region 11. On the other hand, if the width W(x) of the injection window 22 is large, the overall width of the termination region 12 will become large, and thus, it is preferable that the width W(x) be as small as possible. Since the countermeasure against the electric field concentration at the end of the active region 11 is sufficient only near the active region 11, as shown in FIG. Fig. 6, by making the shape of the mask such that the slope of the decrease on a side closer to the active region 11 (x > XN') is greater than the slope of the decrease on a side farther from the active region 11 (x ≤ XN'), it is possible to reduce the total width of the termination region 12 compared to the case of Fig. 3 while taking countermeasures against the electric field concentration at the end of the active region 11. This is the reason why the slope of the decrease in the width W(x) of the injection window 22 is changed.

[0055] In addition, as a result, even in a case where the impurities of the second conductivity type are removed using the single mask 20 with the same dosage profile as that used in Fig. 4 of Example 1 to form the second semiconductor region 2, also has the effect of suppressing a decrease in withstand voltage due to positive interfacial charges, as in the case of Example 2.

[0056] Unlike the above, this example is the same as Example 1, and thus the overlapping description is omitted. Example 4

[0057] Fig. 7 is a diagram illustrating a distance between one injection window and the next injection window on one side of an active area in a mask of Example 4 and a width of the injection window. Fig. 7 shows a diagram that Fig. 3 of Example 1.

[0058] Example 4 differs from Example 1 and Example 3 by the width W(x) of the injection window 22 at the position of distance x.

[0059] The shape of the mask 20 in Example 4 is such that a width W(x) of the injection window 22 at a position of the distance x is substantially equal to a value specified by the following equation (4), where a width of the injection window 22 at a position of a distance XN is defined as Wmax and a width of the injection window 22 as the reference window 22b is defined as Wmin. W(x)=Wmax−(Wmax−Wmin)×(1−x / XN)1 / 2

[0060] In Example 4, the width W(x) of the injection window 22 can be changed smoothly instead of linearly, and a decrease in the withstand voltage due to positive interfacial charges can be suppressed.

[0061] Unlike the above, this example is the same as Example 1 and Example 3, and thus the overlapping description is omitted.

[0062] Although the examples of the present invention have been described above, the present invention is not limited to the configurations described in the examples, and various modifications are possible within the scope of the technical concept of the present invention. In addition, some or all of the configurations described in each example can be combined and applied. List of reference symbols 1 First semiconductor area 2 Second semiconductor area 3 Depletion layer 4 Oxide film 5 Electrode 6 channel stoppers 10 semiconductor device 11 Active area 12, 12a, 12b final area 20 Mask 21 Blocking section 22 injection windows 22a Injection window of the active area 22b Reference window S Distance between the injection window and the next injection window on the side of the active area W Width of the injection window x distance DO dosage amount POS Position QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2014 / 054 319 A1

[0005]

Claims

[1] A method of manufacturing a semiconductor device having, in a periphery of an active region, a termination region in which second semiconductor regions, which are a plurality of well regions having a second conductivity type, are formed in a front surface of a first semiconductor region having a first conductivity type, the second semiconductor regions being formed by injecting impurities of the second conductivity type using a mask as a mask for forming the second semiconductor regions in which a distance S(x) between an injection window at a position of a distance x and the nearest injection window on a side of the active region is substantially equal to a value expressed by S(x) = S max - (S max - S min ) × (x / XN) 1 / 2is specified, wherein, among the second semiconductor regions in which a depletion layer extending into the first semiconductor region is continuous with the active region in a thermal equilibrium state, the injection window corresponding to the second semiconductor region formed at a position farthest from the active region is defined as a reference window, a position of the reference window on one side of the active region is defined as X0, a distance between a position of the injection window adjacent to the active region on one side of the active region and X0 is defined as XN, a distance between the reference window and the nearest injection window on one side of the active region is defined as Smax,a distance between an end portion of the active region and the injection window adjacent to the active region is defined as Smin and a distance from X0 is defined as x., [2] The method of claim 1, wherein in the mask, a width W(x) of the injection window at a position of the distance x decreases with increasing distance from the active region. [3] The method of claim 2, wherein in the mask, a width W(x) of the injection window at a position of the distance x decreases linearly with increasing distance from the active region. [4] The method of claim 2, wherein in the mask, a width W(x) of the injection window at a position of the distance x decreases linearly with increasing distance from the active region, and an inclination of a decrease on a side closer to the active region is larger than an inclination of a decrease on a side farther from the active region. [5] Method according to claim 2, wherein in the mask, a width W(x) of the injection window at a position of distance x is substantially equal to a value defined by W(x) = W max - (W max - W min ) × (1 - x / XN) 1 / 2 is specified, where a width of the injection window at a position of the distance XN is defined as Wmax and a width of the injection window as the reference window is defined as Wmin. [6] The method of claim 1, wherein when the impurities of the second conductivity type are injected using the mask, a dosage amount in the second semiconductor region of the active region is substantially equal to a dosage amount in the second semiconductor region of the termination region. [7] The method of claim 1, wherein when the impurities of the second conductivity type are injected using the mask, a dosage amount in the second semiconductor region on a side closer to the active region in the termination region is larger than a dosage amount in the second semiconductor region on a side farther from the active region in the termination region. [8] A semiconductor device comprising an active region and a termination region formed in a periphery of the active region, wherein the second semiconductor region formed using the method according to any one of claims 1 to 7 is included in the termination region. [9] The semiconductor device according to claim 8, wherein, among the second semiconductor regions, in a range from the second semiconductor region formed by the injection window adjacent to the active region to the second semiconductor region formed by the reference window, in a thermal equilibrium state, the depletion layer spreading into the first semiconductor region is continuous from the active region, each second semiconductor region is a substantially intrinsic region, and depletion of each of the second semiconductor regions occurring due to application of a voltage starts from the second semiconductor region formed by the reference window. [10] The semiconductor device according to claim 8, wherein, among the second semiconductor regions in a range from the second semiconductor region formed by the injection window adjacent to the active region to the second semiconductor region formed by the reference window, a plurality of the second semiconductor regions overlap each other on a side closer to the active region to form a well region, and the second semiconductor regions form the well regions separated from each other on a side farther from the active region.

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