SEMICONDUCTOR COMPONENT

Description

TECHNICAL FIELD

[0001] The present invention relates to a semiconductor device having a trench structure.BACKGROUND ART

[0002] Fig. 12 illustrates an example of a cross-section of a conventional vertically stacked insulated-gate semiconductor device that includes a trench structure. The semiconductor device 9A includes a first n-type semiconductor layer 911, a second n-type semiconductor layer 912, a p-type semiconductor layer 913, an n-type semiconductor region 914, a trench 93, a gate electrode 94 and a gate insulating layer 95.

[0003] The first n-type semiconductor layer 911 serves as the base of the semiconductor device 9A. The second n-type semiconductor layer 912 is provided on the first n-type semiconductor layer 911. The p-type semiconductor layer 913 is provided on the second n-type semiconductor layer 912. The n-type semiconductor region 914 is provided on the p-type semiconductor layer 913.

[0004] The trench 93 is formed so as to penetrate through the n-type semiconductor region 914 and the p-type semiconductor layer 913, and to reach the second n-type semiconductor layer 912. Inside the trench 93, the gate electrode 94 and the gate insulating layer 95 are located. The gate insulating layer 95 serves to insulate the gate electrode 94 from the second n-type semiconductor layer 912, the p-type semiconductor layer 913, and the n-type semiconductor region 914. The gate insulating layer 95 is formed along the inner wall of the trench 93.

[0005] In the semiconductor device 9A thus configured, when a reverse bias is applied, field concentration takes place on the bottom portion of the gate insulating layer 95. The field concentration may provoke dielectric breakdown of the gate insulating layer 95.

[0006] JP-A-H01-192174 describes a semiconductor device arranged to improve breakdown strength while also reducing cell size. WO97 / 47045 discusses a silicon carbide metal-insulator semiconductor field effect transistor having a u-shaped gate trench and an n-type silicon carbide drift layer. US2007 / 194375 discloses a semiconductor device having particular p-type termination layer structure. JP2001-267570 describes a device in which penetration of electric field into a gate oxide film is obstructed using an electric field shielding region. JP 2004-140086 describes a trench gate semiconductor device, with a p-type region of substantially rectangular cross section formed immediately below a bottom surface of the trench.DISCLOSURE OF THE INVENTIONPROBLEM TO BE SOLVED BY THE INVENTION

[0007] It would be desirable to provide a semiconductor device that can suppress the dielectric breakdown in the insulating layer, and a method of manufacturing such semiconductor device.MEANS FOR SOLVING THE PROBLEM

[0008] The invention provides a semiconductor device as set out in claim 1.

[0009] According to claim 1, the semiconductor layer further includes a semiconductor region formed around the trench; one of the first semiconductor layer, the second semiconductor layer, and the semiconductor region may include a recessed portion; and the close portion and the recessed portion may be disposed so as to overlap in a widthwise direction perpendicular to a depthwise direction of the trench.

[0010] Also disclosed, but not claimed, is a method of manufacturing a semiconductor device, comprising forming a trench and a recessed portion on a surface of a semiconductor substrate; forming an insulating layer in the trench; forming a gate electrode over the insulating layer and inside the trench; irradiating the recessed portion with ion thereby forming a first semiconductor region having a different conductivity type from that of the semiconductor substrate, at a position adjacent to a bottom portion of the recessed portion; and irradiating the surface of the semiconductor substrate with ion thereby forming a second semiconductor region having a different conductivity type from that of the semiconductor substrate; wherein the first and the second semiconductor region are formed in connection with each other; and the trench is formed so as to penetrate through the second semiconductor region.

[0011] Other features and advantages of the present invention will become more apparent through detailed description given below referring to the accompanying drawings.

[0012] Fig. 11 shows an embodiment of the claimed invention. The other figures do not show embodiments falling under the scope of the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Fig. 1 is a fragmentary cross-sectional view of a first semiconductor device; Fig. 2 is a fragmentary cross-sectional view for explaining a manufacturing process of the semiconductor device shown in Fig.1; Fig. 3 is a fragmentary cross-sectional view for explaining a manufacturing process following the state shown in Fig. 2; Fig. 4 is a fragmentary cross-sectional view of a second semiconductor device; Fig. 5A is a fragmentary cross-sectional view for explaining a manufacturing process of the semiconductor device shown in Fig. 4; Fig. 5B is a fragmentary cross-sectional view for explaining a manufacturing process following the state shown in Fig. 5A; Fig. 6 is a fragmentary cross-sectional view of a third semiconductor device; Fig. 7 is a fragmentary cross-sectional view of a fourth semiconductor device; Fig. 8A is a fragmentary cross-sectional view for explaining a manufacturing process following the state shown in Fig. 7; Fig. 8B is a fragmentary cross-sectional view for explaining a manufacturing process following the state shown in Fig. 8A; Fig. 9A is a fragmentary cross-sectional view for explaining a manufacturing process following the state shown in Fig. 8B; Fig. 9B is a fragmentary cross-sectional view for explaining a manufacturing process following the state shown in Fig. 9A; Fig. 10 is a fragmentary cross-sectional view for explaining a manufacturing process following the state shown in Fig. 9B; Fig. 11 is a fragmentary cross-sectional view of a fifth semiconductor device according to an embodiment of the present invention; and Fig. 12 is a fragmentary cross-sectional view of a conventional semiconductor device. BEST MODE FOR CARRYING OUT THE INVENTION

[0014] Hereunder, preferred embodiments of the present invention will be described in details, referring to the drawings.

[0015] Fig. 1 illustrates a semiconductor device according to a first example. The semiconductor device A1 according to this example includes a first n-type semiconductor layer 11, a second n-type semiconductor layer 12, a p-type semiconductor layer 13, an n-type semiconductor region 14, a high-concentration p-type semiconductor region 13a, a trench 3, a gate electrode 41, a gate insulating layer 5, a source electrode 42, a drain electrode 43 and an interlayer dielectric 6.

[0016] The first n-type semiconductor layer 11 is a substrate constituted of silicon carbide with a high-concentration impurity added thereto. The second n-type semiconductor layer 12 is provided on the first n-type semiconductor layer 11. The second n-type semiconductor layer 12 is constituted of silicon carbide with a low-concentration impurity added thereto.

[0017] The p-type semiconductor layer 13 includes a first p-type semiconductor layer 131 and a second p-type semiconductor layer 132. The first p-type semiconductor layer 131 is provided on the second n-type semiconductor layer 12. Of the boundary between the first p-type semiconductor layer 131 and the second n-type semiconductor layer 12, a portion along a depthwise direction x of the trench 3 will be referred to as a lateral boundary K1, and a portion along a widthwise direction y will be referred to as a bottom boundary K2. In this example, the bottom boundary K2 is spaced from the boundary between the n-type semiconductor region 14 and the source electrode 42, by approximately 1 µm. The impurity concentration of the first p-type semiconductor layer 131 is, for example, 1x10 17< cm -3< to 1x10 20< cm -3< . The second p-type semiconductor layer 132 is provided on the first p-type semiconductor layer 131 and the second n-type semiconductor layer 12. Of the boundary between the second p-type semiconductor layer 132 and the second n-type semiconductor layer 12, a portion along the widthwise direction y will be referred to as a bottom boundary K3. The impurity concentration of the second p-type semiconductor layer 132 is, for example, 1x10 16< cm -3< to 1x10 19< cm -3< . The n-type semiconductor region 14 is provided on the p-type semiconductor layer 13. The high-concentration p-type semiconductor region 13a is provided on the first p-type semiconductor layer 131.

[0018] The trench 3 is formed so as to penetrate through the n-type semiconductor region 14 and the second p-type semiconductor layer 132, and to reach the second n-type semiconductor layer 12. The trench 3 and the first p-type semiconductor layer 131 are spaced from each other by approximately 0.3 µm, when viewed in the widthwise direction y.

[0019] Inside the trench 3, the gate electrode 41 and the gate insulating layer 5 are located. The gate electrode 41 is constituted of, for example, polysilicon. Alternatively, a metal such as aluminum may be employed to form the gate electrode 41. The gate insulating layer 5 is constituted of silicon dioxide for example, and serves to insulate the gate electrode 41 from the second n-type semiconductor layer 12, the p-type semiconductor layer 13, and the n-type semiconductor region 14. The gate insulating layer 5 is provided along the inner wall of the trench 3 and over the bottom portion and the lateral portion of the trench 3.

[0020] In the depthwise direction x, the bottom boundary K3, the bottom portion of the gate electrode 41, the bottom portion of the trench 3, and the bottom boundary K2 are located in the mentioned order, downwardly in Fig. 1.

[0021] The source electrode 42 is for example constituted of aluminum, and located in contact with the n-type semiconductor region 14 and the high-concentration p-type semiconductor region 13a. The drain electrode 43 is also constituted of aluminum for example, and located in contact with the first n-type semiconductor layer 11. The drain electrode 43 is provided on the opposite side of the first n-type semiconductor layer 11 to the second n-type semiconductor layer 12. The interlayer dielectric 6 is formed so as to cover the gate electrode 41.

[0022] Now, an example of the manufacturing method of the semiconductor device A1 will be described, referring to Figs. 2 and 3.

[0023] Referring first to Fig. 2, a semiconductor substrate which is to serve as the first n-type semiconductor layer 11 is prepared. On the upper surface of the substrate, the second n-type semiconductor layer 12 is formed through epitaxial crystal growth. Then a groove T1 is formed on the surface of the second n-type semiconductor layer 12.

[0024] Referring then to Fig. 3, the first p-type semiconductor layer 131 is formed inside the groove T1 through the epitaxial crystal growth. The surface of the substrate is then planarized. On the planarized substrate, the second p-type semiconductor layer 132 is formed through the epitaxial crystal growth.

[0025] Then a mask of a predetermined pattern is placed over the upper surface of the second p-type semiconductor layer 132, and impurity ions (n-type or p-type) are injected. Thus the n-type semiconductor region 14 and the high-concentration p-type semiconductor region 13a are formed.

[0026] The above is followed by the formation of the trench 3, the gate insulating layer 5 and the gate electrode 41 shown in Fig. 1. Then the interlayer dielectric 6, the source electrode 42, and the drain electrode 43 are formed. Through the foregoing process, the semiconductor device A1 can be obtained.

[0027] The advantageous effects of the semiconductor device A1 will now be described hereunder. In this example device, the bottom boundary K2 is at a lower level than the bottom portion of the trench 3, according to the orientation of Fig. 1. Such configuration encourages the field concentration on the boundary between the first p-type semiconductor layer 131 and the second n-type semiconductor layer 12. Accordingly, the field concentration on the bottom portion of the trench 3 is mitigated. Mitigating the field concentration reduces the risk of dielectric breakdown in the gate insulating layer 5. As a result, the withstand voltage of the semiconductor device A1 can be improved.

[0028] The structure according to this example allows reducing the impurity concentration of the second p-type semiconductor layer 132. This facilitates lowering the threshold voltage of the semiconductor device A1. On the other hand, increasing the impurity concentration of the first p-type semiconductor layer 131 allows suppressing extension of a depletion layer in the first p-type semiconductor layer 131, thereby preventing a punch through phenomenon.

[0029] Figs. 4, 5A and 5B illustrate a second example device. In these drawings, the constituents same as or similar to those of the foregoing example are given the same numeral. The semiconductor device A2 according to this example is different from the semiconductor device A1 according to the first example in including a recessed portion T2.

[0030] In the semiconductor device A2 shown in Fig. 4, the impurity concentration in the first p-type semiconductor layer 131 is higher than that in the second p-type semiconductor layer 132, as in the first embodiment.

[0031] Above the first p-type semiconductor layer 131 according to the orientation of Fig. 4, a recessed portion T2 is provided. In this example, the size of the opening of the recessed portion T2 in the widthwise direction y is slightly smaller than that of the first p-type semiconductor layer 131 in the widthwise direction y. The bottom portion of the recessed portion T2 is located higher than the bottom boundary K2, according to Fig. 4. Also, the bottom portion of the recessed portion T2 is located higher than the bottom boundary K3 in Fig. 4. The high-concentration p-type semiconductor region 13a is located below the recessed portion T2. It is not mandatory that the bottom portion of the recessed portion T2 is located higher than the bottom boundary K3. For example, the bottom portion of the recessed portion T2 may be located lower than the bottom portion of the trench 3. The position of the bottom portion of the recessed portion T2 may be determined irrespective of the position of the bottom boundary K3 and the bottom portion of the trench 3.

[0032] Referring now to Figs. 5A and 5B, an example of the manufacturing method of the semiconductor device A2 will be described hereunder.

[0033] First, as shown in Fig. 5A, a semiconductor substrate which is to serve as the first n-type semiconductor layer 11 is prepared. On the upper surface of the substrate, the second n-type semiconductor layer 12 is formed through the epitaxial crystal growth. Then the recessed portion T2 is formed on the surface of the second n-type semiconductor layer 12, in a depth of approximately 0.5 µm.

[0034] Referring then to Fig. 5B, the first p-type semiconductor layer 131 is formed. To form the first p-type semiconductor layer 131, a mask (not shown) is placed over the upper surface of the substrate, and the recessed portion T2 is irradiated with impurity ions (p-type) from above in Fig. 5B, with energy of approximately 400 KeV. Then the region on the surface of the second n-type semiconductor layer 12 where the recessed portion T2 is not formed is irradiated with impurity ions (p-type), with generally the same energy. As a result, the second p-type semiconductor layer 132 is formed. Here, the ion concentration in the first p-type semiconductor layer 131 and the second p-type semiconductor layer 132 can be controlled by adjusting the duration of the ion irradiation.

[0035] Alternatively, the entire surface of the second n-type semiconductor layer 12 may be irradiated with impurity ions from above in Fig. 5B, without putting the mask on the upper surface of the substrate. By such impurity ion irradiation, the first p-type semiconductor layer 131 and the second p-type semiconductor layer 132 can be formed in different depths from the surface of the second n-type semiconductor layer 12. This process is especially useful in the case where it is not necessary to control the impurity concentration in the first p-type semiconductor layer 131 and the second p-type semiconductor layer 132.

[0036] The above is followed by the formation of the n-type semiconductor region 14 and the high-concentration p-type semiconductor region 13a shown in Fig. 4. These regions can also be formed by injecting impurity ions (n-type or p-type) to the second n-type semiconductor layer 12. Then the trench 3 is formed in the region where the second p-type semiconductor layer 132 has been formed. Inside the trench 3, the gate insulating layer 5 and the gate electrode 41 are formed. Then the interlayer dielectric 6, the source electrode 42, and the drain electrode 43 are formed. Through the foregoing process, the semiconductor device A2 can be obtained.

[0037] According to this example, providing the recessed portion T2 allows forming a deeper portion of the first p-type semiconductor layer 131 by the ion irradiation with lower energy.

[0038] Fig. 6 illustrates a third example device. As in the preceding drawings, the constituents in Fig. 6 same as or similar to those of the foregoing examples are given the same numeral. The semiconductor device A3 according to this example is different from the semiconductor device A2 according to the second example in that the n-type semiconductor region 14 is also provided under the recessed portion T2. Such configuration increases the contact area between the source electrode 42 and the n-type semiconductor region 14. Accordingly, the contact resistance between the source electrode 42 and the n-type semiconductor region 14 can be reduced, in the semiconductor device A3.

[0039] Figs. 7 to 10 illustrate a fourth example device. In these drawings, the constituents same as or similar to those of the foregoing embodiments are given the same numeral. The semiconductor device A4 according to this example is different from the semiconductor device A1 according to the first example in including a p-type semiconductor region 15.

[0040] As is apparent in Fig. 7, the p-type semiconductor region 15 is located in contact with the bottom portion of the trench 3. The impurity concentration in the p-type semiconductor region 15 is, for example, 1x10 16< cm -3< to 1x10 21< cm -3< . The size of the boundary between the p-type semiconductor region 15 and the bottom portion of the trench 3 in the widthwise direction y is slightly smaller than that of the gate electrode 41 in the widthwise direction y. Also, a lowermost portion of the p-type semiconductor region 15 according to the orientation of Fig. 7 is located lower than the bottom boundary K2 in the depthwise direction x. Conversely, although not shown, the bottom boundary K2 may be located lower than the lowermost portion of the p-type semiconductor region 15.

[0041] Referring now to Figs. 8 to 10, an example of the manufacturing method of the semiconductor device A4 will be described hereunder.

[0042] The manufacturing method of the semiconductor device A4 is the same as that of the semiconductor device A1 according to the first example, up to the state shown in Fig. 3. Accordingly, the description of the process up to Fig. 3 is not repeated. Referring thus to Fig. 8A, a plasma CVD is performed over the upper surface of the structure shown in Fig. 3, to thereby form a silicon dioxide layer 7. The silicon dioxide layer 7 serves as the mask for forming the trench 3 and the p-type semiconductor region 15, as will be subsequently described. Proceeding to Fig. 8B, a trench 3' is formed so as to penetrate through all of the silicon dioxide layer 7, the n-type semiconductor region 14, and the p-type semiconductor layer 13. The trench 3' is to be formed into the trench 3 shown in Fig. 7. Then the inner wall of the trench 3' is thermally oxidized (not shown).

[0043] Then as shown in Fig. 9A, a polysilicon layer ps is formed all over the inner wall of the trench 3' and the upper surface of the silicon dioxide layer 7. Then as shown in Figs. 9B and 10, a polysilicon layer ps1 and a polysilicon layer ps3 are removed, leaving a polysilicon layer ps2 unremoved. Impurity ions (p-type) are then injected to the bottom portion of the trench 3', as shown in Fig. 10. At this stage, the p-type semiconductor region 15 is formed. Then the entirety of the silicon dioxide layer 7 and the polysilicon layer ps2 are removed. This is followed by the same process as that described in the first example. Thus, the semiconductor device A4 shown in Fig. 7 can be obtained.

[0044] The advantageous effects of the semiconductor device A4 will now be described hereunder.

[0045] The structure of the semiconductor device A4 allows further mitigating the field concentration on the bottom portion of the trench 3. Accordingly, the withstand voltage of the semiconductor device A4 can be further improved. Here, reducing the size of the p-type semiconductor region 15 in the widthwise direction y allows suppressing an increase in on-resistance.

[0046] Fig. 11 illustrates an embodiment of the present invention. In Fig. 11, the constituents same as or similar to those of the foregoing examples are given the same numeral. A difference between the semiconductor device A5 according to this embodiment and the semiconductor device A4 lies in the shape of the trench 3.

[0047] As shown in Fig. 11, the additional p-type semiconductor layer 15 is provided so as to cover the bottom portion of the trench 3. Such configuration allows further increasing the withstand voltage. Also, the bottom portion of the trench 3 is formed in a trapezoidal shape. As a result, the additional p-type semiconductor layer 15 can be formed within an area overlapping with the trench 3 in the widthwise direction y. The foregoing structure prevents the flow of electron in the semiconductor device A5 from being disturbed, thereby suppressing an increase in on-resistance. Consequently, the dielectric breakdown electric field can be further increased, while an increase in on-resistance can be suppressed.

[0048] The semiconductor device according to the present invention is not limited to the foregoing embodiments. Specific structure and arrangement of the semiconductor device and according to the present invention may be varied in different manners.

Claims

1. A semiconductor device comprising: a semiconductor layer having a first face provided with a trench (3) and a second face opposite to the first face; a p-type semiconductor region (15) located in contact with a bottom portion of the trench; a gate electrode (41) provided in the trench; an insulating layer (5) provided in the trench so as to insulate the semiconductor layer and the gate electrode from each other; and a source electrode (42) disposed at the first face of the semiconductor layer; wherein the semiconductor layer includes an n-type silicon carbide semiconductor substrate (11) with a high concentration impurity, an n-type silicon carbide semiconductor layer (12) with a low-concentration impurity provided on the n-type silicon carbide semiconductor substrate (11), a p-type semiconductor layer (13) provided on the n-type silicon carbide semiconductor layer, the low-concentration impurity being of smaller concentration than the high-concentration impurity, an n-type semiconductor region (14) formed around the trench (3) and provided on the p-type semiconductor layer (13) and held in contact with the source electrode (42), and a high-concentration semiconductor region (13a) of the p-type in contact with the source electrode and extending into the p-type semiconductor layer (13), the high concentration semiconductor region (13a) having a higher impurity concentration than the p-type semiconductor layer (13) and being spaced apart from the n-type silicon carbide semiconductor layer (12), wherein the trench is formed so as to penetrate through the p-type semiconductor layer (13) and to reach the n-type silicon carbide semiconductor layer (12), wherein the p-type semiconductor layer (13) includes a close portion (131) closer to the second face of the semiconductor layer than the trench is, wherein the p-type semiconductor layer (13) includes a channel region formed along the trench and in contact with the n-type silicon carbide semiconductor layer (12), and wherein impurity concentration in the channel region is lower than impurity concentration in the close portion, wherein the n-type silicon carbide semiconductor layer (12) and the close portion (131) of the p-type semiconductor layer define a bottom boundary (K2) at a lower level than the trench, wherein the high-concentration semiconductor region (13a) is located over the close portion (131) in a depthwise direction of the trench; wherein a size of the high-concentration semiconductor region (13a) in the widthwise direction is smaller than the bottom boundary (K2) in the widthwise direction; wherein the bottom portion of the trench (3) is formed in a trapezoidal shape such that the bottom portion of the trench is narrower in the widthwise direction at the trench bottom than at an upper part of the bottom portion of the trench, and the p-type semiconductor region (15) covers the bottom portion of the trapezoidal shape in a manner such that the p-type semiconductor region (15) is formed within an area covered by and shorter than the trench (3) in the widthwise direction.

2. The semiconductor device according to claim 1, wherein the trench (3) and the close portion are spaced apart from each other by approximately 0.3 µm in the widthwise direction.

3. The semiconductor device according to claim 1, wherein the high-concentration semiconductor region (13a) extends through the n-type semiconductor region (14) to contact the source electrode.

4. The semiconductor device according to claim 1, wherein the p-type semiconductor region (15) is formed in the n-type silicon carbide semiconductor layer (12) and spaced from the p-type semiconductor layer (13).

5. The semiconductor device according to claim 1, wherein the impurity concentration of the close portion (131) is from 1x1017 cm-3 to 1x1020cm-3, and the impurity concentration of the channel region is from 1x1016 cm-3 to 1x1019 cm-3.

6. The semiconductor device according to claim 1, wherein the n-type silicon carbide semiconductor layer (12) is an epitaxially grown layer.

7. The semiconductor device according to claim 1, wherein the n-type silicon carbide semiconductor layer (12) is in direct contact with the bottom of the trench.

8. The semiconductor device according to claim 1, further comprising: a drain electrode (43) provided on the n-type silicon carbide semiconductor substrate (11) opposite from the source electrode (43).