JP2013101994A - Diode manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a diode in which a depletion layer is easy to expand form a p-type region to a Schottky contact part.SOLUTION: A manufacturing method of a diode including; an anode electrode formed on one surface of a semiconductor substrate; a cathode electrode formed on another surface of the semiconductor substrate; a p-type region formed in the semiconductor substrate and forming an ohmic contact with the anode electrode; and an n-type region formed in the semiconductor substrate, neighboring the p-type region, forming a Schottky contact with the anode electrode and forming an ohmic contact with the cathode electrode, forms the p-type region by performing a first implantation step of implanting a p-type impurity to the semiconductor substrate through a mask, and a second implantation step of implanting, after the first implantation step, a p-type impurity of the same type of the p-type impurity in the first implantation step into the semiconductor substrate at an impurity depth changed from that in the first implantation step through a mask the same as the mask in the first implantation step.

Description

  The present invention relates to a diode.

  For example, as disclosed in Patent Document 1, a diode in which a Schottky diode and a pn diode are combined is known. In this type of diode, a plurality of p-type regions are discretely formed in a range in contact with the anode electrode. In the range between the p-type regions, the n-type region is Schottky connected to the anode electrode.

  In general, almost no recovery loss occurs in a Schottky diode. For this reason, in the diode in which the Schottky diode and the pn diode described above are combined, the recovery loss can be reduced as compared with a normal pn diode. In general, a Schottky diode is likely to generate a leakage current when a reverse voltage is applied. However, in a diode in which the above Schottky diode and pn diode are combined, a depletion layer spreads from each p-type region to the n-type region when a reverse voltage is applied. The depletion layer pinches off the n-type region between the two p-type regions. Thereby, in this diode, the reverse leakage current in the Schottky diode is suppressed.

JP 2002-314099 A

  In the above-described diode combining a Schottky diode and a pn diode, an n-type region between two p-type regions is formed by a depletion layer extending in a lateral direction (a direction parallel to the surface of the semiconductor substrate) from the p-type region. Pinch off. However, since the distance that the depletion layer extends in the lateral direction is short, the distance between the two p-type regions must be shortened. As a result, the area of the Schottky connection portion is reduced, and recovery loss caused by the diode cannot be significantly reduced. Further, in the technique of Patent Document 1, a wide p-type region is provided at a deep position, thereby narrowing an interval between two p-type regions and securing an area of a Schottky connection portion. However, when such a complicated structure is adopted, there arises a problem that the manufacturing cost of the diode increases. Therefore, the present specification provides a method for manufacturing a diode in which the depletion layer easily spreads from the p-type region to the Schottky connection portion.

  In the diode manufacturing method disclosed in this specification, an anode electrode formed on one surface of a semiconductor substrate, a cathode electrode formed on the other surface of the semiconductor substrate, and a semiconductor substrate are formed in the semiconductor substrate. A p-type region ohmically connected to the anode electrode, and formed in the semiconductor substrate, adjacent to the p-type region, Schottky connected to the anode electrode, and connected to the cathode electrode Thus, a diode having an n-type region that is ohmic-connected is manufactured. In this manufacturing method, a first implantation step of implanting p-type impurities into a semiconductor substrate through a mask, and thereafter, changing the first implantation step and the implantation depth to remove the same p-type impurities as the p-type impurities in the mask. The p-type region is formed by executing a second implantation step of implanting into the semiconductor substrate through the same mask.

  In this manufacturing method, two implantation steps having different implantation depths (first implantation step and second implantation step) are performed using the same mask. Thus, when p-type impurities are implanted at different depths, deep p-type regions can be formed without diffusing the p-type impurities so much thereafter. When the diffusion distance of the p-type impurity is small, the boundary surface between the p-type region and the n-type region constituting the Schottky connection portion can be set to an angle closer to the surface of the semiconductor substrate. As a result, the depletion layer easily extends from the p-type region toward the n-type region constituting the Schottky connection portion. Therefore, according to this manufacturing method, it is possible to manufacture a diode in which reverse leakage current hardly occurs.

The longitudinal cross-sectional view of the diode 10 (vertical cross-sectional view in the II line | wire of FIG. 3). FIG. 3 is an enlarged cross-sectional view of a p-type region 22 of the diode 10. The top view of the diode 10 which abbreviate | omitted illustration of the anode electrode 20. FIG. 3 is a graph showing a distribution of p-type impurity concentration Np and a distribution of electric field E in the p-type region 22 as viewed along the line AA in FIG. Explanatory drawing of the manufacturing method of an Example. Explanatory drawing of the manufacturing method of an Example. Explanatory drawing of the manufacturing method of an Example. The top view of the diode of a modification. The top view of the diode of a modification. The longitudinal cross-sectional view of the conventional diode. The expanded sectional view of the p-type area | region 22 of the conventional diode. 12 is a graph showing the distribution of the p-type impurity concentration Np and the distribution of the electric field E in the p-type region 22 as viewed along the line BB in FIG. Explanatory drawing of the manufacturing method of the conventional diode.

  First, the structure of the diode 10 manufactured by the manufacturing method of the embodiment will be described. As shown in FIGS. 1 and 2, the diode 10 includes a semiconductor substrate 12, an anode electrode 20 formed on the upper surface of the semiconductor substrate 12, and a cathode electrode 28 formed on the lower surface of the semiconductor substrate 12. Yes. A plurality of p-type regions 22, low-concentration n-type regions 24, and high-concentration n-type regions 26 are formed in the semiconductor substrate 12. The plurality of p-type regions 22 are formed at intervals in a range in contact with the anode electrode 20. Each p-type region 22 is ohmically connected to the anode electrode 20. The low concentration n-type region 24 is formed on the side and the lower side of each p-type region 22. The low concentration n-type region 24 is in contact with the anode electrode 20 in a range between the two p-type regions 22. Hereinafter, the low concentration n-type region 24 sandwiched between two p-type regions 22 is referred to as a Schottky connection region 24a. The Schottky connection region 24 a is Schottky connected to the anode electrode 20. The high concentration n-type region 26 is formed below the low concentration n-type region 24. The n-type impurity concentration in the high-concentration n-type region 26 is higher than the n-type impurity concentration in the low-concentration n-type region 24. The high concentration n-type region 26 is ohmically connected to the cathode electrode 28. The anode electrode 20, the low concentration n-type region 24, the high concentration n-type region 26, and the cathode electrode 28 form a Schottky diode. The anode electrode 20, the p-type region 22, the low-concentration n-type region 24, the high-concentration n-type region 26, and the cathode electrode 28 form a pn diode.

  FIG. 3 shows a top view of the diode 10 with the anode electrode 20 omitted. As shown in FIG. 3, three FLRs (Field Limiting Rings) 40 are formed along the outer periphery of the semiconductor substrate 12 in the range exposed on the upper surface of the semiconductor substrate 12. The cross-sectional structure shown in FIG. 1 is formed in a region surrounded by FLR 40 in FIG. As shown in FIG. 3, each p-type region 22 is formed in a stripe shape parallel to each other.

  On the other hand, FIGS. 10 and 11 show a diode manufactured by a conventional manufacturing method (a diode combining a Schottky diode and a pn diode). 10 and 11, the same reference numerals as those in FIGS. 1 and 2 are assigned to the portions corresponding to the respective portions of the diode in FIGS.

  As apparent from comparison between FIGS. 1 and 10, in the diode 10, compared to the conventional diode, the distance between the two p-type regions 22 (that is, the Schottky connection region 24a and the anode electrode 20 is shot). The width of the key-connected part is large.

  2 and 11 indicates the boundary surface between the p-type region 22 and the Schottky connection region 24a (that is, the side boundary surface of the p-type region 22). As is clear from a comparison between FIGS. 2 and 11, in the diode 10, the boundary surface 22 a is formed at an angle closer to perpendicular to the surface of the semiconductor substrate 12 than in the conventional diode.

  4 and 12 show the p-type impurity concentration distribution and the electric field distribution near the boundary surface 22a in the diode 10 and the conventional diode. As is clear from comparison between FIGS. 4 and 12, in the diode 10, the gradient of the p-type impurity concentration in the p-type region 22 is steep in the vicinity of the boundary surface 22a. Therefore, at a position close to the boundary surface 22a (for example, a position 22c at a certain distance from the boundary surface 22a shown in FIGS. 4 and 12), the diode 10 has a higher p-type impurity concentration than the conventional diode.

  Next, the operation of the diode 10 will be described. When a forward voltage is applied to the diode 10, a current flows as indicated by arrows 100 and 102 in FIG. A current path indicated by an arrow 100 is a current path of a Schottky diode. A current path indicated by an arrow 102 is a current path of the pn diode. As described above, in the diode 10, the width of the Schottky connection region 24a is larger than that of the conventional diode shown in FIG. For this reason, as indicated by arrow 100, the current flowing through the current path of the Schottky diode is larger than that of the conventional diode. For this reason, since the effect as a Schottky diode becomes large, when the forward voltage is switched to the reverse voltage, the diode 10 is less likely to cause recovery loss than the conventional diode.

  Further, when a reverse voltage is applied to the diode 10, a depletion layer spreads from the p-type region 22 into the low concentration n-type region 24. In the Schottky connection region 24 a sandwiched between the two p-type regions 22, a depletion layer extends from the p-type regions 22 on both sides as indicated by an arrow 110. As a result, the depletion layer extends over the entire Schottky connection region 24a. That is, the Schottky connection area 24a is pinched off. For this reason, the occurrence of reverse leakage current through the Schottky connection region 24a is suppressed.

  In the diode 10, since the width of the Schottky connection region 24a between the two p-type regions 22 is large, in order to pinch off the Schottky connection region 24a, a large depletion layer is extended in the Schottky connection region 24a. I have to let it. In the diode 10, the depletion layer easily extends in the Schottky connection region 24 a for the following reason.

  The first reason is that, in the diode 10, the side boundary surface 22 a on the side of the p-type region 22 is formed at an angle close to perpendicular to the upper surface of the semiconductor substrate 12. The depletion layer tends to extend in a direction perpendicular to the boundary surface 22 a of the p-type region 22. Therefore, as in the conventional diode shown in FIG. 11, when the boundary surface 22a on the side of the p-type region 22 is greatly inclined, the depletion layer is inclined downward from the p-type region 22 as indicated by an arrow 122. It becomes easy to extend. On the other hand, as shown in FIG. 2, when the boundary surface 22 a is substantially perpendicular to the surface of the semiconductor substrate 12, the depletion layer extends laterally from the p-type region 22 (semiconductor as indicated by an arrow 120 It becomes easy to extend in a direction parallel to the surface of the substrate 12. For this reason, in the diode 10, the depletion layer easily extends in the Schottky connection region 24a.

The second reason is that in the diode 10, the p-type impurity concentration is high in the vicinity of the boundary surface 22 a of the p-type region 22. The distribution of the electric field E in FIGS. 4 and 12 is an electric field distribution when a relatively small reverse voltage (a reverse voltage that does not pinch off the Schottky connection region 24a) is applied to the diode 10 and the conventional diode. 4 and 12, the range where the electric field E is generated (the range where the electric field E is zero or more) is a region where the depletion layer extends. As is apparent from a comparison of FIGS. 4 and 12, the diode 10, since the p-type impurity concentration of the p-type region 22 in the vicinity of the boundary surface 22a high, the distance L ₁ extending the depletion layer in the p-type region 22 decreases, the distance L ₂ extending the depletion layer to the Schottky connection region 24a is large. That is, in the diode 10, the depletion layer easily extends in the Schottky connection region 24 a as compared with the conventional diode.

  Thus, since the depletion layer easily extends in the Schottky connection region 24a, the diode 10 can pinch off the Schottky connection region 24a even if the width of the Schottky connection region 24a is large. For this reason, the diode 10 is unlikely to generate a reverse leakage current. Moreover, since the diode 10 has a large width of the Schottky connection region 24a, recovery loss is less likely to occur than the conventional diode.

  Next, a method for manufacturing the diode 10 will be described. When manufacturing the diode 10, p-type impurities are implanted into the upper surface of the semiconductor substrate 12 in order to form the p-type region 22. 5 to 7 show a p-type impurity implantation step. Note that the low-concentration n-type region 24 has already been formed in the semiconductor substrate 12 before the p-type impurity implantation step.

  In the p-type impurity implantation step, first, as shown in FIG. 5, a mask 50 having an opening 52 is formed on the upper surface of the semiconductor substrate 12.

  Next, as shown in FIG. 5, p-type impurities are implanted into the upper surface of the semiconductor substrate 12. In the range where the mask 50 is formed, the mask 50 prevents the p-type impurity from being implanted into the semiconductor substrate 12. For this reason, the p-type impurity is implanted into the semiconductor substrate 12 in the opening 52. Here, the implantation energy of the p-type impurity is adjusted so that the average stop depth of the p-type impurity implanted into the semiconductor substrate 12 becomes the depth D1 (see FIG. 5). Note that the implantation energy of the p-type impurity can be adjusted by an impurity implantation apparatus.

  Thereafter, the p-type impurity is repeatedly implanted into the upper surface of the semiconductor substrate 12 with the mask 50 formed. In the second and subsequent implantations of the p-type impurity, the implantation energy of the p-type impurity is adjusted so that the average stop depth of the p-type impurity is shallower than the average stop depth at the previous implantation of the p-type impurity. For example, FIG. 6 shows a second p-type impurity implantation. As shown in FIG. 6, in the second p-type impurity implantation, the average stop depth D2 of the p-type impurity implanted into the semiconductor substrate 12 is greater than the average stop depth D1 in the first p-type impurity implantation. The implantation energy of the p-type impurity is adjusted so as to be shallower. In this manner, by repeatedly performing the implantation of the p-type impurity while gradually reducing the implantation depth, the p-type impurity is introduced from the shallow position to the deep position in the semiconductor substrate 12 in the opening 52 as shown in FIG. Injected.

  As shown in FIG. 7, after the p-type impurity is implanted, the semiconductor substrate 12 is subjected to heat treatment. As a result, the p-type impurity implanted into the semiconductor substrate 12 is diffused and activated, and a p-type region 22 is formed as shown in FIGS. Since the p-type impurity is implanted from the shallow position to the deep position in the p-type impurity implantation step, the side boundary surface 22a of the p-type region 22 is located with respect to the upper surface of the semiconductor substrate 12 as shown in FIG. It becomes almost vertical. In addition, since the p-type impurity is implanted from the shallow position to the deep position in the p-type impurity implantation process, the p-type region 22 that extends from the shallow position to the deep position is obtained even if the p-type impurity is not diffused so much in the heat treatment process. Can be formed. When the diffusion distance of the p-type impurity in the heat treatment step is reduced, as shown in FIG. 4, the gradient of the p-type impurity concentration in the p-type region 22 becomes steep in the vicinity of the boundary surface 22a. By forming the anode electrode 20 and the cathode electrode 28 after the heat treatment step, the diode 10 shown in FIG. 1 is completed.

  Next, a manufacturing method of the conventional diode shown in FIGS. In the conventional diode manufacturing method, p-type impurities are implanted into the upper surface of the semiconductor substrate 12 through a mask 60 as shown in FIG. At this time, a p-type impurity is implanted at a position near the surface of the semiconductor substrate 12. That is, here, the implantation energy of the p-type impurity is adjusted so that the average stop depth D3 of the p-type impurity implanted into the semiconductor substrate 12 becomes extremely small. Thereafter, the semiconductor substrate 12 is heat-treated to diffuse and activate the implanted p-type impurity. As a result, a p-type region 22 is formed as shown in FIGS. Since the p-type impurity is implanted only in the vicinity of the surface of the semiconductor substrate 12 in the p-type impurity implantation process, the p-type impurity is diffused to a deep position by increasing the diffusion distance of the p-type impurity in the heat treatment process. In this way, when the p-type region 22 is formed by diffusing the p-type impurity implanted at a shallow position for a long distance, as shown in FIG. 11, the lateral boundary surface 22a and the lower boundary surface of the p-type region 22 are formed. 22 b are smoothly connected, and the boundary surface 22 a is inclined with respect to the upper surface of the semiconductor substrate 12. In addition, when the diffusion distance of the p-type impurity is large as described above, the gradient of the p-type impurity concentration in the p-type region 22 becomes gentle in the vicinity of the boundary surface 22a as shown in FIG.

  As described above, in the manufacturing method of this embodiment, the p-type impurity is implanted into the semiconductor substrate a plurality of times by changing the implantation depth through the same mask. That is, without changing the positional relationship between the mask and the semiconductor substrate, the implantation depth is changed and the p-type impurity is implanted into the semiconductor substrate a plurality of times. Therefore, in the manufacturing method of the present embodiment, the side boundary surface 22a on the side of the p-type region 22 can be formed at an angle close to the vertical with respect to the upper surface of the semiconductor substrate 12 as compared with the conventional manufacturing method. Further, in the manufacturing method of the present embodiment, the gradient of the p-type impurity concentration in the p-type region 22 in the vicinity of the boundary surface 22a can be made steep compared to the conventional manufacturing method. For this reason, the depletion layer easily spreads in the lateral direction from the p-type region 22, and the width between the two p-type regions 22 (the width of the Schottky connection region 24a) can be widened. Therefore, according to the manufacturing method of the present embodiment, it is possible to manufacture the diode 10 that is less likely to cause reverse leakage current and less likely to cause recovery loss than in the past.

  In the manufacturing method of the above-described embodiment, the p-type impurity is repeatedly implanted into the semiconductor substrate while changing the implantation depth through the same mask. However, if the number of implantation times of the p-type impurity is two times or more, how many times. But you can. If the number of injections is 2 or more, the characteristics of the diode can be improved as compared with the conventional case. Further, in the manufacturing method of the above-described embodiment, when the p-type impurity implantation is repeated, the implantation depth is gradually decreased. However, the p-type impurity implantation depth may be changed in any way.

  In the diode 10 described above, the p-type region 22 is formed in a stripe shape as shown in FIG. 3, but may be formed in other shapes. For example, the p-type region 22 may be formed in a circular shape as shown in FIG. 8, or the p-type region 22 may be formed in a lattice shape as shown in FIG.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

10: Diode 12: Semiconductor substrate 20: Anode electrode 22: P-type region 24: Low-concentration n-type region 26: High-concentration n-type region 28: Cathode electrode

Claims (1)

An anode electrode formed on one surface of the semiconductor substrate;
A cathode electrode formed on the other surface of the semiconductor substrate;
A p-type region formed in the semiconductor substrate and ohmically connected to the anode electrode;
An n-type region formed in the semiconductor substrate, adjacent to the p-type region, Schottky connected to the anode electrode, and ohmic connected to the cathode electrode;
A method of manufacturing a diode having
a first implantation step of implanting the p-type impurity into the semiconductor substrate through the mask, and then changing the first implantation step and the implantation depth to pass the same p-type impurity as the p-type impurity through the same mask as the mask. The p-type region is formed by executing a second implantation step for implanting the semiconductor substrate.

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