CN108231866B - Structure and preparation method of silicon carbide Schottky diode with improved surge capability - Google Patents

Abstract

The invention discloses a silicon carbide Schottky diode structure with improved surge capability and a preparation method, wherein the diode structure comprises a silicon carbide substrate of a first conductivity type, a drift layer on the silicon carbide substrate, an anode electrode and a cathode electrode , the surface of the drift layer has a main junction of the second conductivity type; a narrow active region of the second conductivity type, a shallowly doped region of the second conductivity type, a narrow-deeply doped region of the second conductivity type, a Two conductive type wide-deep doped regions and second conductive type active injection regions; a second conductive type terminal injection region is provided on the other side of the main junction; second conductive type narrow active regions, second conductive type shallow The widths of the doped region, the narrow-deep doped region of the second conductivity type, and the wide-deep doped region of the second conductivity type increase in sequence. The structure can prevent the surge current from concentrating on the main junction to reduce the surge capability of the device and improve the surge resistance capability of the device.

Description

Structure and preparation method of silicon carbide Schottky diode with improved surge capability

technical field

The invention belongs to the field of semiconductors and power semiconductors, and in particular relates to a silicon carbide Schottky diode structure and a preparation method for improving surge capability.

Background technique

Compared with other semiconductor materials such as silicon, silicon carbide has a wider band gap, higher critical breakdown electric field, higher saturation drift velocity and thermal conductivity. The characteristics of these superior materials make SiC devices have extremely broad application prospects in the fields of high frequency, high temperature resistance and radiation resistance. Silicon carbide Schottky diodes have high breakdown voltage, high current density and high operating frequency, and have broad development prospects. One of the main bottlenecks facing SiC Schottky diodes is how to improve the surge and avalanche capability of the device.

In order to achieve higher device blocking performance, the SiC Schottky diode realizes a P-type doped region on the surface of the active region by ion implantation, and reduces the surface electric field through the pinch-off effect. By reducing the forward voltage drop generated by the inrush current, the anti-surge capability of the device is improved and the device is prevented from burning. Simulation proves that the larger the width of the P-type doped region, the lower the turn-on voltage of the PN junction; the lower the surface doping concentration of the P-type doped region, the higher the turn-on voltage of the PN junction.

In order to ensure the relative independence of the electric field distribution between the active region and the terminal protection area of the device, the width of the main junction is much larger than the width of the P-type doped region inside the active region. With the increase of forward voltage, the main junction part is turned on first. Due to the participation of minority carriers in conduction, the on-current of the device increases rapidly, so most of the surge current of the device is concentrated in the main junction part, and the main junction part is only partially metallized , too concentrated inrush current will cause the device to burn out. Due to the small width of the P-type region inside the active region, the conduction voltage of the PN junction is too high, which cannot play a role in anti-surge.

SUMMARY OF THE INVENTION

Purpose of the invention: In view of the problems in the prior art, the present invention discloses a structure and a preparation method of a silicon carbide Schottky diode with improved surge capability. At the same time, it can greatly improve the hindering effect of the main junction and its adjacent areas on the current, thereby avoiding the reduction of the avalanche resistance caused by the excessive concentration of avalanche current in the main junction area, and improving the avalanche resistance of the device.

Technical scheme: the present invention adopts the following technical scheme:

One aspect of the present invention discloses a silicon carbide Schottky diode structure with improved surge capability, comprising a first conductivity type silicon carbide substrate (1), a drift layer (2) on the silicon carbide substrate, an anode electrode ( 13) and a cathode electrode (14), the surface of the drift layer has a second conductivity type main junction (11); on one side of the main junction (11) is provided a second conductivity type narrow active region (5), a second conductivity type A conductive type shallow doped region (6), a second conductive type narrow-deep doped region (7), a second conductive type wide-deep doped region (8), and a second conductive type active implant region (9); A second conductive type terminal implantation region (10) is provided on the other side of the main junction (11); the width of the second conductive type narrow active region (5) is smaller than that of the second conductive type shallowly doped region ( 6) width; the depth of the second conductivity type narrow active region (5) is equal to the depth of the second conductivity type shallowly doped region (6); the width of the second conductivity type shallowly doped region (6) is smaller than that of the second conductivity type The width of the type narrow-deep doped region (7); the depth of the second conductivity type shallowly doped region (6) is less than the depth of the second conductivity type narrow-deep doped region (7); the second conductivity type narrow-deep The width of the doped region (7) is smaller than the width of the second conductivity type wide-deeply doped region (8); the depth of the second conductivity type narrow-deeply doped region (7) is equal to the second conductivity type wide-deeply doped Depth of zone (8).

There are multiple active injection regions (9) of the second conductivity type, and each of the active injection regions (9) of the second conductivity type has a uniform width and a uniform spacing.

The second conductive type narrow active region (5), the second conductive type shallowly doped region (6), the second conductive type narrow-deep doped region (7), the second conductive type wide-deeply doped region (8) The surface doping concentration of the main junction (11) is higher than the inner doping concentration; the second conductive type narrow active region (5), the second conductive type shallow doping region (6), the second conductive type narrow active region (5), the second conductive type The conductive type narrow-deeply doped region (7), the second conductive type wide-deeply doped region (8) and the surface doping concentration of the main junction (11) are lower than that of the second conductive type active implant region (9) doping concentration.

The second conductive type terminal implantation region (10) is doped with low concentration; the second conductive type active implantation region (9) is doped with high concentration.

As a preference, an open groove is provided on the surface of the main junction (11), and the bottom of the open groove is a concave surface; the depth of the open groove is less than 1/2 of the injection depth of the main junction.

Another aspect of the present invention discloses a preparation method of a silicon carbide Schottky diode with improved surge capability, comprising the following steps:

(S1) growing a first conductivity type drift layer (2) on the first conductivity type silicon carbide substrate (1);

(S2) making a first implantation mask medium (3) on the surface of the drift layer (2);

(S3) making a second implantation mask medium (4) on the surface of the drift layer (2);

(S4) forming a second conductive type main junction (11), a second conductive type narrow active region (5), a second conductive type shallowly doped region (6), and a second conductive type narrow-deep doping by an ion implantation process impurity region (7), second conductivity type wide-deeply doped region (8);

(S5) removing the first implanted mask medium (3) and the second implanted mask medium (4);

(S6) making a third implantation mask medium (19) on the surface of the drift layer (2);

(S7) forming a second conductive type terminal implantation region (10) through an ion implantation process;

(S8) removing the implantation mask medium (19);

(S9) making a fourth implantation mask medium (12) on the surface of the drift layer (2);

(S10) forming an active implantation region (9) of a second conductivity type by an ion implantation process;

(S11) removing the implantation mask medium (12);

(S12) An anode electrode (13) and a cathode electrode (14) are fabricated.

The step (S11) further includes the following steps after removing the implanted mask medium (12):

The surface of the main junction (11) is grooved and etched to form an open groove; the bottom of the open groove is a concave surface; the depth of the open groove is less than 1/2 of the injection depth of the main junction.

The second conductive type narrow active region (5), the second conductive type shallowly doped region (6), the second conductive type narrow-deep doped region (7), the second conductive type wide-deeply doped region (8) The surface doping concentration of the main junction (11) is higher than the inner doping concentration; the second conductive type narrow active region (5), the second conductive type shallow doping region (6), the second conductive type narrow active region (5), the second conductive type The conductive type narrow-deeply doped region (7), the second conductive type wide-deeply doped region (8) and the surface doping concentration of the main junction (11) are lower than that of the second conductive type active implant region (9) doping concentration.

Beneficial effects: when the device is conducting in the forward direction, its surge capability is particularly important. When the device is instantaneously flooded with a large amount of current by the inductance, it is required that the voltage drop of the device should not be too high. In the diode structure disclosed in the present invention, the second conductive type terminal implantation region 10 is low-doped, and the surface doping concentration of the main junction 11 is higher than its internal doping concentration but lower than the doping concentration of the second conductive type active implantation region 9 impurity concentration. In this way, the on-voltage is high, so that the inrush current cannot pass through, and the main junction will not bear the inrush current. All the surge current is completed by the P-type doped region inside the active region; at the same time, four regions 5, 6, 7 and 8 with low surface doping are designed, similar to the main junction, the regions 5, 6, 7 and 8 are The surface doping concentration is higher than its internal doping concentration but lower than the doping concentration of the second conductivity type active implant region 9, and the surge turn-on voltage of regions 5, 6, 7 and 8 is higher than that of the second conductivity type active implant The region 9 is injected into the region 9, so during the surge, the region 9 is opened first, so that the inrush current mainly relies on the region 9 to conduct conduction, which improves the uniformity of the inrush current. In addition, the setting of the doping concentration of the region 10 and the region 11 makes the resistance of the main junction and the adjacent regions larger, which prevents the avalanche current from concentrating on the edge of the anode 13 in the main junction region, while the setting of the region 5 moves the avalanche current further to the Inside the source region, the avalanche resistance of the device is improved.

Description of drawings

Figure 1 is a schematic diagram of the device material structure;

FIG. 2 is a schematic diagram of the first injection of the mask medium;

FIG. 3 is a schematic diagram of the second injection of the mask medium;

4 is a schematic diagram of the first ion implantation;

5 is a schematic diagram of removing the mask dielectric after the first ion implantation;

FIG. 6 is a schematic diagram of the third injection of the mask medium;

7 is a schematic diagram of the second ion implantation;

8 is a schematic diagram of removing the mask dielectric after the second ion implantation;

9 is a schematic diagram of the fourth injection of the mask medium;

10 is a schematic diagram of the third ion implantation;

11 is a schematic diagram of removing the mask dielectric and making a cathode after the third ion implantation;

Fig. 12 is the structural schematic diagram after making the anode;

Figure 13 shows the main junction and the second conductive type narrow active region (5), the second conductive type shallowly doped region (6), the second conductive type narrow-deep doped region (7), the second conductive type wide- the doping profile of the deeply doped region (8);

FIG. 14 is a doping curve diagram of the second conductivity type terminal implantation region;

15 is a doping graph of the second conductivity type active implant region;

Figure 16 is a schematic view of the structure of the opening slot in Example 2;

17 is a schematic diagram of the diode structure of Embodiment 2;

FIG. 18 is a schematic diagram of the cross-sectional shape of the bottom of the open groove in Example 2. FIG.

Detailed ways

The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments.

Example 1:

In order to prevent the surge current from concentrating on the main junction, which leads to the decrease of the surge capability of the device, and at the same time improve the blocking effect of the main junction and its surrounding areas on the current, avoid the avalanche tolerance of the main junction area caused by excessive concentration of avalanche current, and improve the device's avalanche resistance. , the present invention discloses a silicon carbide Schottky diode structure, as shown in FIG. 12 , comprising a silicon carbide substrate 1 of a first conductivity type, a drift layer 2 located on the silicon carbide substrate, an anode electrode 13 and a cathode electrode 14 , the surface of the drift layer has a second conductive type main junction 11; on one side of the main junction 11, a second conductive type narrow active region 5, a second conductive type shallowly doped region 6, a second conductive type narrow- A deeply doped region 7 , a second conductive type wide-deep doped region 8 , and a second conductive type active implantation region 9 ; a second conductive type terminal implantation region 10 is provided on the other side of the main junction 11 .

When the device is in forward conduction, with the increase of forward voltage, the main junction part is turned on first. The width of the active region 5 is smaller than the width of the second conductive type shallowly doped region 6; the depth of the second conductive type narrow active region 5 is equal to the depth of the second conductive type shallowly doped region 6; the second conductive type shallowly doped region The width of the region 6 is smaller than the width of the second conductive type narrow-deep doping region 7; the depth of the second conductive type shallow doping region 6 is smaller than the depth of the second conductive type narrow-deep doping region 7; the second conductive type narrow - the width of the deeply doped regions 7 is smaller than the width of the second conductivity type wide-deeply doped regions 8; . In this way, the surge turn-on voltage of the second conductive type narrow active region 5 is higher than the surge turn-on voltage of the second conductive type shallowly doped region 6; the surge turn-on voltage of the second conductive type shallowly doped region 6 is higher than The surge turn-on voltage of the two conductive type narrow-deep doped regions 7; the surge turn-on voltage of the second conductive type narrow-deep doped region 7 is higher than the surge turn-on voltage of the second conductive type wide-deep doped region 8 . The isolation of the doped regions 5 , 6 , 7 and 8 prevents the main junction from being turned on due to excessive current under the main junction 11 .

The optimal width of area 5 is between 0.5μm and 1.5μm; the optimal width of area 6 is between 1μm and 2.5μm; the optimal width of area 7 is between 1μm and 3μm; the optimal width of area 8 is 1.5μm Between μm and 4.5 μm; the optimum width of region 9 is between 1.5 μm and 4.5 μm.

In order to reduce the on-resistance when the PN junction is turned on and improve the surge capability, the second conductive type narrow active region 5, the second conductive type shallow doped region 6, the second conductive type narrow-deep doped region 7, the second conductive type The surface doping concentration of the type wide-deep doping region 8 and the main junction 11 is higher than its internal doping concentration and lower than the doping concentration of the second conductivity type active implant region (9). The doping concentration curve is shown in the figure 13, the ion implantation depth of the surface highly doped region 15 is less than 0.4 μm, the doping concentration is higher than 5e18cm ⁻³ , and the doping concentration of the inner low doped region 16 is lower than 5e18cm ⁻³ .

There are multiple second conductivity type active injection regions 9, and each second conductivity type active injection region 9 has the same width and spacing; this can ensure the uniformity of the electric field intensity distribution on the device surface in the blocking state.

The second conductivity type terminal ^implantation region 10 is doped with low concentration, and its doping concentration curve is shown in FIG. 14 . Region 9 is doped with high concentration, and the doping concentration curve is shown in FIG. 15 .

The preparation method of the above-mentioned silicon carbide Schottky diode comprises the following steps:

(S1) growing the first conductivity type drift layer 2 on the first conductivity type silicon carbide substrate 1, as shown in FIG. 1;

(S2) making a first implantation mask medium 3 on the surface of the drift layer 2, as shown in FIG. 2;

(S3) making a second implantation mask medium 4 on the surface of the drift layer 2, as shown in FIG. 3;

(S4) Forming the second conductive type main junction 11, the second conductive type narrow active region 5, the second conductive type shallow doped region 6, the second conductive type narrow-deep doped region 7, the second conductive type narrow-deep doped region 7, the second conductive type The conductive type wide-deep doped region 8 is shown in Figure 4; the doping concentration curves of the regions 5, 6, 7, 8, and 11 are shown in Figure 13;

(S5) removing the first implanted mask medium 3 and the second implanted mask medium 4, as shown in FIG. 5;

As can be seen from Figures 3 and 4, the regions 5, 6, 7, 8 are made together. Since there is a masking medium 3 on the surfaces of 5 and 6, and there is a removal step in step (S5), the highly doped parts on the surfaces of regions 5 and 6 are removed, while the surfaces of regions 7 and 8 are not implanted with masking medium, thus including High and low doped fractions. However, the surface doping concentration of the regions 7 and 8 is still lower than that of the region 9, so when a surge occurs, the region 9 opens first.

(S6) making a third implantation mask medium 19 on the surface of the drift layer 2, as shown in FIG. 6;

(S7) forming the second conductive type terminal implantation region 10 through an ion implantation process, as shown in FIG. 7 , and the doping concentration curve of the region 10 is shown in FIG. 14 ;

(S8) removing the implantation mask medium 19, as shown in FIG. 8;

(S9) making a fourth implantation mask medium 12 on the surface of the drift layer 2, as shown in FIG. 9;

( S10 ) forming an active implantation region 9 of the second conductivity type by an ion implantation process, as shown in FIG. 10 , and the doping concentration curve of the region 9 is shown in FIG. 15 ;

(S11) removing the implantation mask medium 12, as shown in FIG. 11;

(S12) The anode electrode 13 and the cathode electrode 14 are fabricated, so far, the structure of the silicon carbide Schottky diode with improved surge capability disclosed in the present invention is obtained, as shown in FIG. 12 .

Example 2:

Although the SiC Schottky diode structure in Embodiment 1 can improve the surge and avalanche capability of the device, it is still relatively easy to cause avalanche current concentration in the terminal region at the edge of the anode 13 . This embodiment further improves it, so that the avalanche current moves to the inside of the active region.

The structure of the SiC Schottky diode disclosed in this embodiment is shown in FIG. 17 . The surface of the main junction 11 is grooved and etched, and then the anode 20 and the cathode 21 are fabricated. The anode electrode 20 also adopts a grooved structure on the surface of the main junction 11, so that in the avalanche state, the avalanche current is not easy to concentrate on the edge of the anode, but moves to the inside of the active area, so that a uniform avalanche occurs in the active area.

As shown in FIG. 16 , the structure of the opening groove 23 on the surface of the main junction 11 is the structure, and the depth 22 of the opening groove is less than 1/2 of the implantation depth D11 of the main junction 11 . The bottom of the open groove is concave, and the cross-section of the bottom is shown by curve 24 in FIG. 18 . Curve 25 and curve 26 in FIG. 18 are schematic cross-sectional views of a plane and a convex surface, respectively, and the bottom of the opening groove 23 in this embodiment should avoid these two shapes.

In the preparation method of the silicon carbide Schottky diode in Embodiment 1, after removing the implanted mask medium 12 in step (S11), the following steps are further included: trench etching is performed on the surface of the main junction (11) to form an open trench; The bottom of the open groove is concave; the depth of the open groove is less than 1/2 of the injection depth of the main junction, and then the anode 20 and the cathode 21 are fabricated, which is the method for fabricating a SiC Schottky diode disclosed in this embodiment.

Claims (10)

1. A silicon carbide Schottky diode structure for improving surge capability, comprising a first conductivity type silicon carbide substrate (1), a drift layer (2) on the silicon carbide substrate, an anode electrode (13) and a cathode The electrode (14) is characterized in that the surface of the drift layer has a main junction (11) of the second conductivity type; A conductive type shallow doped region (6), a second conductive type narrow-deep doped region (7), a second conductive type wide-deep doped region (8), and a second conductive type active implant region (9); A second conductive type terminal implantation region (10) is provided on the other side of the main junction (11); the width of the second conductive type narrow active region (5) is smaller than that of the second conductive type shallowly doped region ( 6) width; the depth of the second conductivity type narrow active region (5) is equal to the depth of the second conductivity type shallowly doped region (6); the width of the second conductivity type shallowly doped region (6) is smaller than that of the second conductivity type The width of the type narrow-deep doped region (7); the depth of the second conductivity type shallowly doped region (6) is less than the depth of the second conductivity type narrow-deep doped region (7); the second conductivity type narrow-deep The width of the doped region (7) is smaller than the width of the second conductivity type wide-deeply doped region (8); the depth of the second conductivity type narrow-deeply doped region (7) is equal to the second conductivity type wide-deeply doped Depth of zone (8). 2 . The silicon carbide Schottky diode structure with improved surge capability according to claim 1 , wherein the second conductivity type active injection regions ( 9 ) are multiple, and each second conductivity type has a 2. 3 . The source implantation regions (9) have the same width and the same spacing. 3. The silicon carbide Schottky diode structure with improved surge capability according to claim 1, wherein the second conductive type narrow active region (5) and the second conductive type shallowly doped region (6) ), the second conductive type narrow-deeply doped region (7), the second conductive type wide-deeply doped region (8) and the main junction (11) have surface doping concentrations higher than their internal doping concentrations; the Second conductivity type narrow active region (5), second conductivity type shallowly doped region (6), second conductivity type narrow-deeply doped region (7), second conductivity type wide-deeply doped region (8) ) and the surface doping concentration of the main junction (11) are lower than the doping concentration of the second conductivity type active implant region (9); the inner doping concentration is lower than 5e18cm ⁻³ . 4. The silicon carbide Schottky diode structure with improved surge capability according to claim 3, wherein the doping concentration of the second conductive type terminal implantation region (10) is smaller than that of the second conductive type active implantation The doping concentration of the region (9); the doping concentration of the second conductive type terminal implantation region (10) is lower than 5e18cm ⁻³ . 5 . The SiC Schottky diode structure with improved surge capability according to claim 1 , wherein an open groove is provided on the surface of the main junction ( 11 ), and the bottom of the open groove is a concave surface. 6 . 6 . The SiC Schottky diode structure with improved surge capability according to claim 5 , wherein the depth of the opening groove is less than 1/2 of the implantation depth of the main junction. 7 . 7. A method for preparing a silicon carbide Schottky diode for improving surge capability, comprising the steps of: (S1) growing a first conductivity type drift layer (2) on the first conductivity type silicon carbide substrate (1); (S2) making a first implantation mask medium (3) on the surface of the drift layer (2); (S3) making a second implantation mask medium (4) on the surface of the drift layer (2); (S4) forming a second conductive type main junction (11), a second conductive type narrow active region (5), a second conductive type shallowly doped region (6), and a second conductive type narrow-deep doping by an ion implantation process impurity region (7), second conductivity type wide-deeply doped region (8); (S5) removing the first implanted mask medium (3) and the second implanted mask medium (4); (S6) making a third implantation mask medium (19) on the surface of the drift layer (2); (S7) forming a second conductive type terminal implantation region (10) through an ion implantation process; (S8) removing the implanted mask medium (19); (S9) making a fourth implantation mask medium (12) on the surface of the drift layer (2); (S10) forming an active implantation region (9) of a second conductivity type by an ion implantation process; (S11) removing the implantation mask medium (12); (S12) An anode electrode (13) and a cathode electrode (14) are fabricated. 8. The method for preparing a silicon carbide Schottky diode with improved surge capability according to claim 7, wherein the step (S11) further comprises the following steps after removing the implanted mask medium (12): The surface of the main junction (11) is grooved and etched to form an open groove; the bottom of the open groove is a concave surface. 9 . The method for manufacturing a silicon carbide Schottky diode with improved surge capability according to claim 8 , wherein the depth of the opening groove is less than 1/2 of the implantation depth of the main junction. 10 . 10. The method for manufacturing a silicon carbide Schottky diode with improved surge capability according to claim 7, wherein the second conductive type narrow active region (5) and the second conductive type shallowly doped region ( 6), the second conductive type narrow-deep doping region (7), the second conductive type wide-deep doping region (8) and the main junction (11) have a surface doping concentration higher than their internal doping concentration; The second conductive type narrow active region (5), the second conductive type shallowly doped region (6), the second conductive type narrow-deeply doped region (7), the second conductive type wide-deeply doped region ( 8) and the surface doping concentration of the main junction (11) is lower than the doping concentration of the active implant region (9) of the second conductivity type.

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