Method of forming short-circuiting regions for insulated gate semiconductor devices

Abstract: The present invention provides a method of manufacturing a semiconductor device, comprising the steps of selectively diffusing an impurity of a first conductivity type and another impurity of a second conductivity type into a main surface region of a semiconductor substrate (21) so as to form first semiconductor regions (22) of the first conductivity type and second semiconductor regions (23) of the second conductivity type, forming a first semiconductor layer (25) of the second conductivity type on the semiconductor substrate (21), said first semiconductor layer (25) being of at least a single layer structure, forming element regions (26, 27, 28, 29) of the first and second conductivity types by thermal diffusion of impurities into the first semiconductor layer (25), and polishing the opposite main surface of the semiconductor substrate (21) to expose the first semiconductor regions (22) of the first conductivity type and the second semiconductor regions (23) of the second conductivity type. The first semiconductor layer (25) may be of a laminate structure consisting of a plurality of semiconductor layers differing from each other in the impurity concentration.

Description: The present invention relates to a method of manufacturing a semiconductor device such as an IGBT or a thyristor. In general, a semiconductor device such as an IGBT or a thyristor is widely used as a switching element such as an inverter for controlling, for example, a motor. In order to diminish the power conversion loss, the switching element of this type is required to be operated at a high speed and to be turned on at a low forward voltage. Fig. 1 shows an n - -channel type IGBT widely known to the art. As shown in the drawing, the conventional n - -channel type IGBT comprises a gate electrode 1, emitter electrodes 2, 3, a gate oxide film 4, emitter regions 5, 6, p-type base regions 7, 8, an n - -type layer 9, an n + -type buffer layer 10, and a collector electrode 12. In manufacturing the IGBT shown in Fig. 1, used is a wafer comprising a p-type semiconductor layer of a high impurity concentration, an n-type semiconductor layer of a high impurity concentration formed on the p-type semiconductor layer, and an n-type semiconductor layer of a low impurity concentration formed on the n-type layer of the high impurity concentration. The IGBT is obtained by forming element regions in the surface region of the wafer by means of thermal diffusion of impurities. Fig. 2 shows a conventional anode short-circuit type IGBT. The anode short-circuit type IGBT shown in Fig. 2 is substantially equal to the IGBT shown in Fig. 1, except that, in the IGBT shown in Fig. 2, the p + -type layer 11 in Fig. 1 is replaced by a layer 13 consisting of p-type regions and n-type regions which are formed alternately. Incidentally, the reference numerals common with Figs. 1 and 2 denote the same members of the IGBT. The anode short-circuit type IGBT of this type is superior to the ordinary IGBT in the relationship between the switching characteristics and the on-voltage, particularly, in the relationship on the side of a low current. In the manufacture of an ordinary semiconductor element, it is necessary for the semiconductor wafer used to have a thickness of at least about 250 µm where the wafer has a diameter of 5 inches. It should be noted that various steps such as a diffusion step, an etching step and a patterning step are involved in the manufacture of the semiconductor element. Naturally, the semiconductor wafer is transferred several times in the manufacturing process of the semiconductor element, with the result that, the wafer, if unduly thin, is likely to be cracked in the transfer step. When it comes to the IGBT, the optimum thickness of the n + -type buffer layer 10 shown in Fig. 2 is about 15 µm. On the other hand, the optimum thickness of the n - -type layer 9 depends on the grade of the withstand voltage. In the case of an IGBT having a withstand voltage of 1200 V, which has a large demand, the optimum thickness of the n - -type layer 9 is about 100 µm. In this case, the total thickness of the n - -type layer 9 and the n + -type buffer layer 10 is only about 115 µm. It follows that, in the case of manufacturing an IGBT element by using a wafer having a diameter of 5 inches, it is necessary for the layer 13 to have a thickness of at least about 140 µm. What should be noted is that, if the layer 13 has such a large thickness, it is practically impossible to diffuse an n-type impurity through the back surface of the wafer to form an anode short-circuit structure as shown in Fig. 2. To be more specific, a very long diffusion time is required for the n-type impurity diffused through the back surface of the wafer to reach the n + -type buffer layer 10. In addition, the impurity in the n + -type buffer layer 10 is also diffused during the diffusion step, resulting in failure to obtain an ideal concentration profile of the impurity in the n + -type buffer layer 10. Such being the situation, it was substantially impossible to obtain an anode short-circuit structure exhibiting satisfactory characteristics. Patent Abstracts of Japan, vol. 11, No. 41 (E-478) [2488], 1987, and JP-A-61 208 268 disclose an anode short circuit type conduction modulation type semiconductor device, wherein the turn-off characteristics shall be improved by preventing the unnecessary thick formation of a drain region and forming an impurity region short-circuiting with an anode corresponding to a gate layer in narrow and sufficient depth size. Especially, N-type substrates are prepared by selectively introducing P-type impurity from one surface thereof. Then, these substrates are joined at the surface where the P-type impurity has been introduced in mirror shape. Thereafter, the outer surfaces are cut and removed and the formation of the semiconductor device is proceeded by applying silicon dioxide and forming gate layer at one surface of the composite substrate. A plurality of reverse conduction type regions and gate layers are formed etc. EP-A-0 080 044 relates to a semiconductor device having rapid removal of majority carriers from an active base region thereof at device turn-off. Regions are selectively formed in the substrate before an epitaxial layer is formed thereon. Various regions N ++ and P ++ are described. It is the object of the present invention to provide a method of manufacturing a semiconductor device of an anode short-circuit structure, which comprises a thin n - -type layer having a withstand voltage of about 2000 V or less and an n + -type buffer layer having an ideal impurity concentration profile. This object is solved by a method as described in new claims 1 and 2, respectively. The subclaims show advantageous further developments of the invention. Especially, according the present invention, the method of manufacturing a semiconductor device, comprises the steps of: selectively diffusing an impurity of a first conductivity type and another impurity of a second conductivity type into a main surface region of a semiconductor substrate so as to form first semiconductor regions of the first conductivity type and second semiconductor regions of the second conductivity type; selectively forming third semiconductor regions of the first conductivity type and fourth semiconductor regions of the second conductivity type in the opposite main surface region of the semiconductor substrate by selectively diffusing impurities of the first and second conductivity types into the substrate through the opposite main surface, wherein the third and fourth semiconductor regions are positioned to be aligned with the first and second semiconductor regions, respectively; combining the first and third semiconductor regions to form regions of the first conductivity type extending through the substrate and the second and fourth semiconductor regions to form regions of the second conductivity type, by continuing the above diffusing steps or by a heat treatment after the above diffusing steps; forming a first semiconductor layer of the second conductivity type on the semiconductor substrate, said first semiconductor layer being of at least a single layer structure; and forming element regions of the first and second conductivity types by thermal diffusion of impurities into said first semiconductor layer. Further, according to the present invention, the method of manufacturing a semiconductor device, comprises the steps of: selectively diffusing an impurity of a second conductivity type having a high concentration into a main surface region of a semiconductor substrate of a first conductivity type so as to form third semiconductor regions; forming a second semiconductor layer of the first or second conductivity type having a low impurity concentration on the surface of the semiconductor substrate; selectively forming first semiconductor regions of the first conductivity type and second semiconductor regions of the second conductivity type in the second semiconductor layer by selective diffusion of impurities, wherein the second semiconductor regions are positioned to be aligned with the third semiconductor regions; combining the first and third semiconductor regions to form regions of the first conductivity type extending through the second semiconductor layer and the second semiconductor regions and the semiconductor substrate to form regions of the second conductivity type extending through the second semiconductor layer by continuing the above diffusing steps or by a heat treatment after the above diffusing steps; forming a first semiconductor layer of the second conductivity type on the semiconductor substrate, said first semiconductor layer being of at least a single layer structure; and forming element regions of the first and second conductivity types by thermal diffusion of impurities into said first semiconductor layer. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a cross sectional view showing a conventional n - -channel type IGBT; Fig. 2 is a cross sectional view showing a conventional anode short-circuit type IGBT; Fig. 3 is a cross sectional view showing a step of manufacturing a semiconductor device according to a first embodiment not forming part of the present invention; Fig. 4 is a cross sectional view showing other steps of manufacturing a semiconductor device according to the first embodiment not forming part of the present invention; Fig. 5 is a cross sectional view showing further steps of manufacturing a semiconductor device according to the first embodiment not forming part of the present invention; Fig. 6 is a cross sectional view showing a step of manufacturing a semiconductor device according to a second embodiment forming part of the present invention; Fig. 7 is a cross sectional view showing another step of manufacturing a semiconductor device according to the second embodiment forming part of the present invention; Fig. 8 is a cross sectional view showing other steps of manufacturing a semiconductor device according to the second embodiment forming part of the present invention; Fig. 9 is a cross sectional view showing further steps of manufacturing a semiconductor device according to the second embodiment forming part of the present invention; Fig. 10 is a cross sectional view showing a step of manufacturing a semiconductor device according to a third embodiment forming part of the present invention; Fig. 11 is a cross sectional view showing other steps of manufacturing a semiconductor device according to the third embodiment forming part of the present invention; Fig. 12 is a cross sectional view showing another step of manufacturing a semiconductor device according to the third embodiment forming part of the present invention; Fig. 13 is a cross sectional view showing other steps of manufacturing a semiconductor device according to the third embodiment forming part of the present invention; Fig. 14 is a cross sectional view showing further steps of manufacturing a semiconductor device according to the third embodiment forming part of the present invention; Fig. 15 is a cross sectional view showing a step of manufacturing a semiconductor device according to a fourth embodiment forming part of the present invention; Fig. 16 is a cross sectional view showing other steps of manufacturing a semiconductor device according to the fourth embodiment forming part of the present invention; Fig. 17 is a cross sectional view showing another step of manufacturing a semiconductor device according to the fourth embodiment forming part of the present invention; Fig. 18 is a cross sectional view showing other steps of manufacturing a semiconductor device according to the fourth embodiment forming part of the present invention; Fig. 19 is a cross sectional view showing further steps of manufacturing a semiconductor device according to the fourth embodiment forming part of the present invention; Fig. 20 is a cross sectional view showing a step of manufacturing a semiconductor device according to a fifth embodiment not forming part of the present invention; Fig. 21 is a cross sectional view showing other steps of manufacturing a semiconductor device according to the fifth embodiment not forming part of the present invention; Fig. 22 is a cross sectional view showing other steps of manufacturing a semiconductor device according to the fifth embodiment not forming part of the present invention; Fig. 23 is a cross sectional view showing a step of manufacturing a semiconductor device according to a sixth embodiment not forming part of the present invention; Fig. 24 is a cross sectional view showing other steps of manufacturing a semiconductor device according to the sixth embodiment not forming part of the present invention; and Fig. 25 is a cross sectional view showing further steps of manufacturing a semiconductor device according to the sixth embodiment not forming part of the present invention. Let us describe the six embodiments which are applied to the manufacture of an n - -channel IGBT. First Embodiment This embodiment which does not form part of the claimed invention comprises the manufacturing steps shown in Figs. 3 to 5. In the first step, p-type regions 22 having a high impurity concentration and n-type regions 23 having a high impurity concentration are selectively formed by diffusing a p-type impurity and an n-type impurity into a p-type semiconductor substrate 21, as shown in Fig. 3. The p-type semiconductor substrate 21 has a thickness of 400 µm. In the next step, an n + -type buffer layer 24 having a thickness of 15 µm and an n - -type layer 25 having a thickness of 105 µm are successively formed in this order on the p-type regions 22 and the n-type regions 23, as shown in Fig. 4. In this step, the thickness of the entire system is about 520 µm. Then, element regions including p-type base regions 26, 27, n + -type emitter regions 28, 29, a gate oxide film 30, emitter electrodes 31, 32 and a gate electrode 33 are successively formed in the surface region of the n - -type layer 25. Further, the back surface of the semiconductor substrate is polished to diminish its thickness by about 370 µm so as to expose the p-type regions 22 having a high impurity concentration and the n-type regions 23 having a high impurity concentration. After the polishing treatment, a metal thin film 34 acting as a collector electrode is deposited on the polished surface to cover the p-type regions 22 and the n-type regions 23 so as to manufacture an anode short-circuit type IGBT. Second Embodiment This embodiment corresponds to claim 1 and comprises the manufacturing steps shown in Figs. 6 to 9. In the first step, p-type regions 36 having a high impurity concentration and n-type regions 37 having a high impurity concentration are selectively formed by diffusing a p-type impurity and an n-type impurity into a main surface region of a p-type semiconductor substrate 35, as shown in Fig. 6. In the next step, p-type regions 38 having a high impurity concentration and n-type regions 39 having a high impurity concentration are formed by diffusing a p-type impurity and an n-type impurity into a main back surface region of the p-type semiconductor substrate 35, as shown in Fig. 7. It should be noted that these p-type regions 38 and the n-type regions 39 formed in the back surface region of the semiconductor substrate 35 are positioned to be aligned in the vertical direction in the drawing with the p-type regions 36 and the n-type regions 37 formed in said one main surface (or front surface) region of the semiconductor substrate 35. The impurity diffusion is continued until the p-type regions 36 and 38 formed in the front and back surface regions of the semiconductor substrate 35 are joined each other to form p-type regions 40 extending across the semiconductor substrate 35, as shown in Fig. 8. Likewise, the n-type regions 37 and 39 formed in the front and back surface regions of the semiconductor substrate 35 are joined each other to form n-type regions 41 extending across the semiconductor substrate 35. Alternatively, it is possible to form these p-type regions 40 and the n-type regions 41 by a heat treatment for the impurity diffusion after formation of the p-type regions 38 and the n-type regions 39 in the back surface region of the semiconductor substrate. Then, an n + -type buffer layer 42 having a thickness of 15 µm and an n - -type layer 43 having a thickness of 105 µm are successively formed in this order on the p-type regions 40 and the n-type regions 41, as shown in Fig. 8. In this step, the thickness of the entire system is about 520 µm. Then, element regions including p-type base regions 44, 45, n + -type emitter regions 46, 47, a gate oxide film 48, emitter electrodes 49, 50 and a gate electrode 51 are successively formed in the surface region of the n - -type layer 43. The impurity types of the regions and layers may be reversed. It is certainly possible to obtain an anode short-circuit type IGBT by directly depositing a metal thin film on the back surface of the p-type semiconductor substrate 35. However, it is desirable to diminish the thickness of the chip in order to improve the heat dissipation of the element. To be more specific, the back surface of the p-type semiconductor substrate 35 is polished to diminish its thickness by about 200 µm. After the polishing treatment, a metal thin film 52 acting as a collector electrode is deposited on the polished surface to cover the p-type regions 40 and the n-type regions 41 so as to manufacture an anode short-circuit type IGBT which permits dissipating heat efficiently. Third Embodiment This embodiment corresponds to claim 2 and comprises the manufacturing steps shown in Figs. 10 to 14. In the first step, n-type regions 54 having a high impurity concentration are selectively formed by diffusing an n-type impurity into a main surface region of a p + -type semiconductor substrate 53, as shown in Fig. 10. The substrate 53 has an impurity concentration of 1 × 10 19 atoms/cm 2 , and a thickness of 400 µm. Also, the n-type regions 54 are formed to have a depth of about 5 µm. In the next step, a p - -type layer 55 having a low impurity concentration is formed to have a thickness of about 20 µm by epitaxial growth on the surface of the substrate 53 as shown in Fig. 11, followed by selectively forming p-type regions 56 having a high impurity concentration and n-type regions 57 having a high impurity concentration by diffusing a p-type impurity and an n-type impurity into a surface region of the epitaxial layer 55. It should be noted that these n-type regions 57 formed in the epitaxial layer 55 are positioned to be aligned in the vertical direction in the drawing with the n-type regions 54 formed in said one main surface (or front surface) region of the semiconductor substrate 53. The impurity diffusion is continued until the n-type regions 57 having a high impurity concentration, which are formed in the surface region of the epitaxial layer 55, are joined to the n-type regions 54 formed in the substrate 53 to form n-type regions 58 having a larger area, as shown in Fig. 12. Likewise, the p-type regions 56 formed in a surface region of the epitaxial layer 55 are joined to the p-type semiconductor substrate 53 having a high impurity concentration so as to form p-type regions 59 having a large area. Alternatively, it is possible to form these p-type regions 59 and the n-type regions 58 by a heat treatment for the impurity diffusion after formation of the p-type regions 56 and the n-type regions 57 in the surface region of the epitaxial layer 55. Then, an n + -type buffer layer 60 having a thickness of 15 µm and an n - -type layer 61 having a thickness of 105 µm are successively formed in this order on the p-type regions 59 and the n-type regions 58, as shown in Fig. 13. In the next step, element regions including p-type base regions 62, 63, n + -type emitter regions 64, 65, a gate oxide film 66, emitter electrodes 67, 68 and a gate electrode 69 are successively formed in the surface region of the n - -type layer 61. In this step, the thickness of the entire system is about 520 µm. Then, the back surface of the p-type semiconductor substrate 53 is polished to diminish its thickness by about 390 µm. After the polishing treatment, a metal thin film 70 acting as a collector electrode is deposited on the polished surface to cover the p-type regions 59 having a high impurity concentration and the n-type regions 58 having a high impurity concentration so as to manufacture an anode short-circuit type IGBT which permits dissipating heat efficiently. In this embodiment, each of the p-type regions 59 and the n-type regions 58 has a high impurity concentration, with the result that a satisfactory ohmic contact can be achieved between these diffusion regions and the metal thin film (collector electrode) 70. Fourth Embodiment This embodiment also corresponds to claim 2 and comprises the manufacturing steps shown in Figs. 15 to 19. In the first step, p-type regions 74 having a high impurity concentration are selectively formed by diffusing a p-type impurity into a main surface region of an n + -type semiconductor substrate 73, as shown in Fig. 15. The substrate 73 has an impurity concentration of 1 × 10 19 atoms/cm 2 , and a thickness of 400 µm. Also, the p-type regions 74 are formed to have a depth of about 5 µm. In the next step, a p - -type layer 55 having a low impurity concentration is formed to have a thickness of about 20 µm by epitaxial growth on the surface of the substrate 73 as shown in Fig. 16, followed by selectively forming p-type regions 56 having a high impurity concentration and n-type regions 57 having a high impurity concentration by diffusing a p-type impurity and an n-type impurity into a surface region of the epitaxial layer 55. It should be noted that these p-type regions 56 formed in the epitaxial layer 55 are positioned to be aligned in the vertical direction in the drawing with the p-type regions 74 formed in said one main surface (or front surface) region of the semiconductor substrate 73. The impurity diffusion is continued until the p-type regions 56 having a high impurity concentration, which are formed in the surface region of the epitaxial layer 55, are joined to the p-type regions 74 formed in the substrate 73 to form p-type regions 78 having a larger area, as shown in Fig. 17. Likewise, the n-type regions 57 formed in a surface region of the epitaxial layer 55 are joined to the n-type semiconductor substrate 73 having a high impurity concentration so as to form n-type regions 79 having a large area. Alternatively, it is possible to form these p-type regions 78 and the n-type regions 79 by a heat treatment for the impurity diffusion after formation of the p-type regions 56 and the n-type regions 57 in the surface region of the epitaxial layer 55. Then, an n + -type buffer layer 60 having a thickness of 15 µm and an n - -type layer 61 having a thickness of 105 µm are successively formed in this order on the p-type regions 78 having a high impurity concentration and the n-type regions 79 having a high impurity concentration, as shown in Fig. 18. In the next step, element regions including p-type base regions 62, 63, n + -type emitter regions 64, 65, a gate oxide film 66, emitter electrodes 67, 68 and a gate electrode 69 are successively formed in the surface region of the n - -type layer 61. In this step, the thickness of the entire system is about 520 µm. Then, the back surface of the n-type semiconductor substrate 73 having a high impurity concentration is polished to diminish its thickness by about 390 µm so as to expose the n-type regions 79 having a high impurity concentration and the p-type regions 78 having a high impurity concentration. After the polishing treatment, a metal thin film 70 acting as a collector electrode is deposited on the polished surface to cover the p-type regions 78 having a high impurity concentration and the n-type regions 79 having a high impurity concentration so as to manufacture an anode short-circuit type IGBT which permits dissipating heat efficiently. In this embodiment, each of the p-type regions 78 and the n-type regions 79 has a high impurity concentration, with the result that a satisfactory ohmic contact can be achieved between these diffusion regions and the metal thin film (collector electrode) 70. Fifth Embodiment This embodiment which does not form part of the claimed invention comprises the manufacturing steps shown in Figs. 20 to 22. In the first step, n-type regions 23 having a high impurity concentration are selectively formed to have a depth of about 50 µm by diffusing an n-type impurity into a p-type semiconductor substrate 21, as shown in Fig. 20. The p-type semiconductor substrate 21 has a thickness of 400 µm. In the next step, an n + -type buffer layer 24 having a thickness of 15 µm and an n - -type layer 25 having a thickness of 105 µm are successively formed in this order on the surface of the semiconductor substrate 21 including the n-type diffusion layers 23, as shown in Fig. 21. In this step, the thickness of the entire system is about 520 µm. Then, element regions including p-type base regions 26, 27, n + -type emitter regions 28, 29, a gate oxide film 30, emitter electrodes 31, 32 and a gate electrode 33 are successively formed in the surface region of the n - -type layer 25. Further, the back surface of the semiconductor substrate 21 is polished to diminish its thickness by about 370 µm so as to expose the n-type regions 23 having a high impurity concentration. After the polishing treatment, a metal thin film 34 acting as a collector electrode is deposited on the polished surface so as to manufacture an anode short-circuit type IGBT. Sixth Embodiment This embodiment which does not form part of the claimed invention comprises the manufacturing steps shown in Figs. 23 to 25. In the first step, p-type regions 22 having a high impurity concentration are selectively formed by diffusing a p-type impurity into a main surface region of an n-type semiconductor substrate 81 having a thickness of 400 µm, as shown in Fig. 23. These p-type regions 22 are formed in a depth of about 50 µm. Then, an n + -type buffer layer 24 having a thickness of 15 µm and an n - -type layer 25 having a thickness of 105 µm are successively formed in this order on the surface of the substrate 81 including the p-type regions 22, as shown in Fig. 24. In this step, the thickness of the entire system is about 520 µm. Then, element regions including p-type base regions 26, 27, n + -type emitter regions 28, 29, a gate oxide film 30, emitter electrodes 31, 32 and a gate electrode 33 are successively formed in the surface region of the n - -type layer 25. Then, the back surface region of the n-type semiconductor substrate 81 is polished to diminish its thickness by about 370 µm to expose the p-type regions 22 of a high impurity concentration. After the polishing treatment, a metal thin film 34 acting as a collector electrode is deposited on the polished surface so as to manufacture an anode short-circuit type IGBT. As described above in detail, the present invention provides methods of manufacturing a semiconductor device of an anode short-circuit structure, which comprises a thin n - -type layer having a withstand voltage of about 2000 V or less and an n + -type buffer layer having an ideal impurity concentration profile. The semiconductor device manufactured by the method of the present invention exhibits a satisfactory relationship between the switching characteristics and the on-voltage. Particularly, the relationship in the low current region can be markedly improved in the present invention, compared with the conventional IGBT.

Claims: Method of manufacturing a semiconductor device, comprising the steps of: selectively diffusing an impurity of a first conductivity type and another impurity of a second conductivity type into a main surface region of a semiconductor substrate (35) so as to form first semiconductor regions (36) of the first conductivity type and second semiconductor regions (37) of the second conductivity type; selectively forming third semiconductor regions (38) of the first conductivity type and fourth semiconductor regions (39) of the second conductivity type in the opposite main surface region of the semiconductor substrate (35) by selectively diffusing impurities of the first and second conductivity types into the substrate (35) through the opposite main surface, wherein the third and fourth semiconductor regions (38, 39) are positioned to be aligned with the first and second semiconductor regions (36, 37), respectively; combining the first and third semiconductor regions (36, 38) to form regions (40) of the first conductivity type extending through the substrate and the second and fourth semiconductor regions (37, 39) to form regions (41) of the second conductivity type extending through the substrate, by continuing the above diffusing steps or by a heat treatment after the above diffusing steps; forming a first semiconductor layer (43) of the second conductivity type on the semiconductor substrate (35), said first semiconductor layer (43) being of at least a single layer structure; and forming element regions (44, 45, 46, 47) of the first and second conductivity types by thermal diffusion of impurities into said first semiconductor layer (43). Method of manufacturing a semiconductor device, comprising the steps of: selectively diffusing an impurity of a second conductivity type having a high concentration into a main surface region of a semiconductor substrate (53) of a first conductivity type so as to form third semiconductor regions (54) ; forming a second semiconductor layer (55) of the first or second conductivity type having a low impurity concentration on the surface of the semiconductor substrate (53); selectively forming first semiconductor regions (56) of the first conductivity type and second semiconductor regions (57) of the second conductivity type in the second semiconductor layer (55) by selective diffusion of impurities, wherein the second semiconductor regions (57) are positioned to be aligned with the third semiconductor regions (54) ; combining the first and third semiconductor regions (57, 54) to form regions (58) of the first conductivity type extending through the second semiconductor layer and the second semiconductor regions (56) and the semiconductor substrate (53) to form regions (59) of the second conductivity type, extending through the second semiconductor layer (55), by continuing the above diffusing steps or by a heat treatment after the above diffusing steps; forming a first semiconductor layer (61) of the second conductivity type on the semiconductor substrate (53), said first semiconductor layer (61) being of at least a single layer structure; and forming element regions (62, 63, 64, 65) of the first and second conductivity types by thermal diffusion of impurities into said first semiconductor layer (43). The method according to claim 2, further comprising the step of polishing the opposite main surface of the semiconductor substrate (53) to expose the semiconductor regions (58, 59) of the first and second conductivity types. The method according to claim 1, further comprising the step of polishing the opposite main surface of the semiconductor substrate (35). The method according to any of the preceding claims, characterized in that said first conductivity type means an n-type-conductivity and said second conductivity type means a p-type conductivity. The method according to any of claims 1-4 characterised in that said first conductivity type means a p-type conductivity and said second conductivity type means an n-type conductivity. The method according to any of the preceding claims, characterized in that said first semiconductor layer (43, 61) is of a laminate structure consisting of a plurality of semiconductor layers differing from each other in their impurity concentration.

Inventors: TSUNODA TETSUJIRO, TSUNODA, TETSUJIRO, TSUNODA, TETSUJIRO, C/O INTELLECTUAL PROPERTY DIV.
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1993
Main classification: H01L21
IPC codes: H01L29, H01L21