A silicon carbide trench junction barrier Schottky diode and preparation method thereof

Abstract

The present invention relates to a silicon carbide trench junction barrier Schottky diode and a preparation method, belonging to the technical field of semiconductor devices. The silicon carbide trench junction barrier Schottky diode comprises, from bottom to top, an ohmic contact cathode metal layer; a silicon carbide substrate layer of a first conductivity type; a first epitaxial layer of a first conductivity type, a plurality of ion implantation regions of a second conductivity type; a second epitaxial layer of a first conductivity type, which is epitaxially grown on the first epitaxial layer of the first conductivity type and grown on the plurality of ion implantation regions of the second conductivity type; a plurality of trenches formed in the ion implantation regions of the second conductivity type; a Schottky metal layer and an anode metal layer. The Schottky diode of the present invention has a simple process flow, low leakage current and high breakdown voltage, and low forward conduction voltage, and good comprehensive performance.

Description

Technical Field

[0001] The invention relates to a silicon carbide trench junction barrier Schottky diode and a preparation method thereof, belonging to the technical field of semiconductor devices. Background Art

[0002] Because silicon carbide has a wider bandgap, higher thermal conductivity, higher electron saturation rate and higher critical breakdown electric field than silicon, devices made from it can withstand harsh conditions such as high temperature and high pressure, making up for the shortcomings of traditional silicon materials and having broad application prospects in power devices.

[0003] As the earliest commercialized power device, the silicon carbide Schottky diode has only electrons as carriers, low on-voltage and fast switching speed. However, it is significantly affected by the barrier lowering effect under high voltage conditions, and the reverse tunneling current is particularly large, resulting in a small breakdown voltage, which limits its application in high voltage fields. At the same time, the PiN diode has a large breakdown voltage, but a long reverse recovery time and a large on-voltage, resulting in large switching losses. Therefore, the junction barrier Schottky diode injects the P-type region at the Schottky contact, which not only inherits the fast switching speed and low on-voltage of the Schottky diode, but also has the high voltage resistance of the PiN diode, and has become the mainstream of the silicon carbide diode market.

[0004] The trench junction barrier Schottky diode is a further improvement of the junction barrier Schottky diode. By making grooves and then injecting the P-type region, the formed junction barrier is deeply embedded in the device while keeping the injection energy unchanged. The introduction of the trench structure increases the junction depth of the PN junction, which can more effectively shield the Schottky surface electric field and reduce the tunneling current. However, the trench will aggravate the JFET effect, increase the on-voltage, and play a negative role in the conduction of the forward current.

[0005] In the prior art, PN junctions are usually formed by etching trenches first and then ion implantation to increase the junction depth and avoid implantation of too high energy. However, due to the scattering effect of the mask on the ion beam and the fact that the ion beam used for implantation is not absolutely perpendicular to the wafer surface, the trench sidewalls are inevitably implanted, which easily causes sidewall damage and introduces defects, increases the PN junction area, and increases the on-state voltage.

[0006] Therefore, a diode and a preparation method thereof are needed which have a simple process flow, low leakage current, high breakdown voltage, and low forward conduction voltage. Summary of the invention

[0007] In view of the deficiencies in the prior art, the present invention provides a silicon carbide trench junction barrier Schottky diode and a preparation method thereof, which can solve the problem that the existing diodes have to sacrifice their reverse leakage current and reverse breakdown voltage when achieving a smaller forward conduction voltage, which is not conducive to improving the overall performance of the diode.

[0008] Terminology explanation:

[0009] The first conductivity type is n-doped or n-type, and the second conductivity type is p-doped or p-type.

[0010] The term Schottky contact is used to describe a metal-semiconductor junction that exhibits rectifying properties.

[0011] Ohmic contact is intended to describe two elements or parts of a semiconductor device that are in direct mechanical contact and ohmically connected.

[0012] The technical solution of the present invention is as follows:

[0013] A silicon carbide trench junction barrier Schottky diode, the silicon carbide trench junction barrier Schottky diode comprising, from bottom to top, an ohmic contact cathode metal layer, a silicon carbide substrate layer of a first conductivity type, a first epitaxial layer of the first conductivity type, and a second epitaxial layer of the first conductivity type;

[0014] A first epitaxial layer of a first conductivity type is epitaxially grown on a silicon carbide substrate layer of the first conductivity type, and a plurality of ion implantation regions of a second conductivity type are formed on the surface through ion implantation, and a second epitaxial layer of the first conductivity type above the ion implantation regions of the second conductivity type is provided with a groove, and the bottom and the corner of the groove extend deep into the ion implantation region of the second conductivity type;

[0015] A Schottky metal layer is provided on the second epitaxial layer of the first conductivity type and at the bottom and sidewalls of the trench, and an anode metal layer is provided on the Schottky metal layer. The bottom and side of the trench and the upper surface of the second epitaxial layer of the first conductivity type form Schottky contacts with the Schottky metal layer.

[0016] Preferably, the lateral width of the trench is smaller than the lateral width of the second conductivity type ion implantation region.

[0017] Preferably, the doping concentration of the second epitaxial layer of the first conductivity type is greater than that of the first epitaxial layer of the first conductivity type, the thickness of the second epitaxial layer of the first conductivity type is 1-2 μm, and the doping concentration ranges from 1×10 16 cm -3 -1x10 17 cm -3 .

[0018] Preferably, the plurality of ion implantation regions of the second conductivity type in the first epitaxial layer of the first conductivity type have equal spacing, and the thickness of the ion implantation regions of the second conductivity type is 0.3-1 μm.

[0019] Preferably, the ions implanted into the second conductivity type ion implantation region are boron ions or phosphorus ions.

[0020] Preferably, the ion implantation region of the second conductivity type has a Gaussian doping distribution, and the peak concentration is not less than 1×10 17 cm -3 .

[0021] Preferably, the first conductive type silicon carbide substrate layer is made of 4H-SiC, has a thickness of 300-350 μm, has a doping source of nitrogen or phosphorus, and has a low resistivity of 0.014-0.028 Ω∙m.

[0022] Preferably, the material selection of the Schottky metal layer includes Ta, Co, Mo, Ti, Ni, Cr, Pt, Pd, Zr, W and mixtures of two or more thereof; the anode metal layer is Al, and the ohmic contact cathode metal layer is Ti / Ni / Ag.

[0023] The present invention also provides a method for preparing a silicon carbide trench junction barrier Schottky diode, the steps of which are as follows:

[0024] (1) preparing a silicon carbide substrate layer of a first conductivity type made of silicon carbide by in-situ growing a first epitaxial layer of the first conductivity type;

[0025] (2) forming an ion implantation region of the second conductivity type in the first epitaxial layer of the first conductivity type by an ion implantation process; the upper surface of the ion implantation region is 0.2 μm away from the upper surface of the first epitaxial layer of the first conductivity type;

[0026] (3) During the secondary epitaxial regrowth process, the upper surface layer needs to be removed to a certain extent before any regrowth to ensure a clean surface before the new epitaxial layer starts growing again. If there is a P-type region on the surface layer before the second epitaxial layer is regrown, removing the upper surface layer may contaminate the system. By injecting the P-type region deeper, the P-type region can be avoided from being etched, thus preventing contamination of the system;

[0027] Removing an upper surface layer with a thickness of 0.2 μm on an upper surface of the first epitaxial layer of the first conductivity type, and forming a second epitaxial layer of the first conductivity type on the upper surface of the first epitaxial layer of the first conductivity type by epitaxial growth;

[0028] (4) forming a trench in the second epitaxial layer of the first conductivity type by dry plasma etching;

[0029] (5) forming a Schottky metal layer on the bottom and side of the trench and the upper surface of the second epitaxial layer of the first conductivity type by a sputtering deposition process;

[0030] (6) Forming an anode metal layer and an ohmic contact cathode metal layer on the surface of the Schottky metal layer and the first conductive type silicon carbide substrate layer respectively by depositing metal, and then laser annealing the ohmic contact cathode metal layer to form an ohmic contact.

[0031] Preferably, in step (5), in order to improve the characteristics of the Schottky contact, Schottky annealing is preferably performed after the Schottky metal layer is formed, and the temperature of the Schottky annealing is preferably 300° C. to 800° C.

[0032] The beneficial effects of the present invention are:

[0033] The second epitaxial layer of the first conductivity type of the present invention is doped with high concentration, the number of carriers is increased, the on-resistance is reduced, and a low forward conduction voltage can be achieved.

[0034] The present invention adopts a method of ion implantation followed by secondary epitaxy. During the secondary epitaxy, the implanted ions are activated and annealed, thus avoiding a separate annealing process and surface degradation caused by activation annealing, thus simplifying the process steps and improving device quality.

[0035] The present invention adopts a preparation method of first ion implantation followed by secondary epitaxy and then trench etching, so that the trench sidewalls are not implanted with ions, thus avoiding damage and defects of the trench sidewalls due to ion implantation, improving the quality of the device, avoiding the formation of PN junctions on the trench sidewalls to reduce the Schottky contact area, and not increasing the forward conduction voltage.

[0036] The lateral width of the groove of the present invention is smaller than the lateral width of the second conductive type ion implantation area, and the bottom corner of the groove is located inside the second conductive type ion implantation area, so that the etching step does not need to be strictly aligned, and the groove corner can be effectively protected to avoid premature breakdown caused by corner electric field concentration, greatly reducing leakage current and achieving high breakdown voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a cross-sectional schematic diagram of the present invention;

[0038] Figure 2 It is a cross-sectional schematic diagram after forming a first epitaxial layer of a first conductivity type according to the present invention;

[0039] Figure 3 It is a cross-sectional schematic diagram after forming the ion implantation region of the second conductivity type according to the present invention;

[0040] Figure 4 It is a cross-sectional schematic diagram after forming a second epitaxial layer of the first conductivity type according to the present invention;

[0041] Figure 5 It is a cross-sectional schematic diagram after the groove is formed in the present invention;

[0042] Figure 6 It is a cross-sectional schematic diagram after the Schottky metal layer is formed in the present invention;

[0043] Figure 7 It is a schematic diagram of the structure of a traditional junction barrier Schottky diode;

[0044] Figure 8 This is a comparison diagram of the forward characteristics of the present invention and the traditional structure;

[0045] Fig. 9 A comparison diagram of reverse characteristics between the present invention and the traditional structure;

[0046] Among them, 1. a silicon carbide substrate layer of a first conductive type, 2. a first epitaxial layer of a first conductive type, 3. an ion implantation region of a second conductive type, 4. a second epitaxial layer of a first conductive type, 5. a trench, 6. a Schottky metal layer, 7. an anode metal layer, and 8. an ohmic contact cathode metal layer. DETAILED DESCRIPTION

[0047] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the drawings in the implementation of this specification, but are not limited to this. Anything not fully described in the present invention shall be based on the conventional technology in the art.

[0048] Embodiment 1:

[0049] The embodiment of the present application first introduces the structure of a silicon carbide trench junction barrier Schottky diode device.

[0050] like Figure 1 As shown, the silicon carbide trench junction barrier Schottky diode includes, from bottom to top, an ohmic contact cathode metal layer 8; a silicon carbide substrate layer 1 of a first conductivity type; a first epitaxial layer 2 of a first conductivity type, which is epitaxially grown on the silicon carbide substrate layer 1 of the first conductivity type; a plurality of ion implantation regions 3 of a second conductivity type; a second epitaxial layer 4 of a first conductivity type, which is epitaxially grown on the first epitaxial layer 2 of the first conductivity type and grown on the plurality of ion implantation regions 3 of the second conductivity type; a Schottky metal layer 6 and an ohmic contact anode metal layer 7.

[0051] Grooves are arranged inside the second epitaxial layer 4 of the first conductivity type above the ion implantation region of the second conductivity type, and the bottom and corners of the grooves extend deep into the ion implantation region of the second conductivity type. A Schottky metal layer is arranged above the second epitaxial layer of the first conductivity type and at the bottom and sidewalls of the grooves, and an anode metal layer is arranged above the Schottky metal layer. The bottom and side of the groove and the upper surface of the second epitaxial layer 4 of the first conductivity type form Schottky contact with the Schottky metal layer 6.

[0052] The lateral width of the trench is smaller than the lateral width of the second conductivity type ion implantation region 3 .

[0053] The doping concentration of the second epitaxial layer 4 of the first conductivity type is greater than that of the first epitaxial layer 2 of the first conductivity type. The thickness of the second epitaxial layer 4 of the first conductivity type is 1.5 μm, and the doping concentration range is 4×10 16 cm -3 .

[0054] The plurality of second conductivity type ion implantation regions 3 have equal spacing, the second conductivity type ion implantation region thickness is 0.7 μm, the second conductivity type ion implantation region has a Gaussian doping distribution, and the maximum doping concentration is not less than 1×10 17 cm -3 .

[0055] Embodiment 2:

[0056] A silicon carbide trench junction barrier Schottky diode, the structure of which is as described in Example 1, except that the thickness of the second epitaxial layer of the first conductivity type is 1 μm, and the doping concentration range is 1×10 16 cm -3 The first conductive type silicon carbide substrate layer is made of 4H-SiC, has a thickness of 300 μm, a doping source of nitrogen, and a low resistivity of 0.014 Ω∙m.

[0057] Embodiment 3:

[0058] A silicon carbide trench junction barrier Schottky diode, the structure of which is as described in Example 1, except that the thickness of the second epitaxial layer of the first conductivity type is 2 μm, and the doping concentration range is 1×10 17 cm -3 The first conductive type silicon carbide substrate layer is made of 4H-SiC, has a thickness of 350 μm, has a doping source of phosphorus, and has a low resistivity of 0.028 Ω∙m.

[0059] Embodiment 4:

[0060] The present application embodiment provides a method for preparing the silicon carbide trench junction barrier Schottky diode described in Example 1, and the steps are as follows:

[0061] (1) If Figure 2 As shown, a silicon carbide substrate layer 1 of a first conductivity type made of silicon carbide is prepared, and a first epitaxial layer 2 of the first conductivity type is grown by in-situ epitaxy. The silicon carbide substrate layer of the first conductivity type is made of 4H-SiC, has a thickness of 320 μm, has a doping source of nitrogen, and has a low resistivity of 0.02 Ω∙m. The thickness and doping concentration of the first epitaxial layer of the first conductivity type should be adjusted accordingly according to the change of the operating voltage. The operating voltage of this embodiment is 1200 V, so the thickness is 10 μm.

[0062] (2) If Figure 3 As shown, an ion implantation region 3 of a second conductivity type is formed inside the first epitaxial layer 2 of the first conductivity type by an ion implantation process, the implanted ions are boron ions or phosphorus ions, and the thickness of the ion implantation region is 0.3 μm; the upper surface of the ion implantation region is 0.2 μm away from the upper surface of the first epitaxial layer of the first conductivity type;

[0063] (3) During the secondary epitaxial regrowth process, the upper surface layer needs to be removed to a certain extent before any regrowth to ensure a clean surface before the new epitaxial layer starts growing again. If there is a P-type region on the surface before the second epitaxial layer is regrown, removing the upper surface layer may contaminate the system. By injecting the P-type region deeper, etching the P-type region can be avoided to prevent contamination of the system.

[0064] like Figure 4 As shown, a 0.2 μm thick upper surface layer is removed from the upper surface of the first epitaxial layer of the first conductivity type, and a second epitaxial layer 4 of the first conductivity type with a higher doping concentration is formed on the upper surface of the first epitaxial layer 2 of the first conductivity type by epitaxial growth to reduce the forward conduction voltage of the device. The temperature of epitaxial growth is usually around 1600°C. This epitaxial growth step activates and anneals the ions implanted in the previous step while growing the epitaxial layer, and no separate activation annealing process is required.

[0065] (4) If Figure 5 As shown, a trench 5 is formed in the second epitaxial layer 4 of the first conductivity type by dry plasma etching. The etching steps do not need to be strictly aligned. The bottom and corners of the trench 5 penetrate deep into the ion implantation area 3 of the second conductivity type, effectively protecting the trench corners.

[0066] (5) Figure 6As shown, a Schottky metal layer 6 is formed at the bottom, side and upper surface of the second epitaxial layer 4 of the first conductivity type in the trench by a sputtering deposition process, and forms a Schottky contact with the first epitaxial layer 2 of the first conductivity type and the second epitaxial layer 4 of the first conductivity type. The Schottky metal layer can be, but is not limited to, Ta, Co, Mo, Ti, Ni, Cr, Pt, Pd, Zr, W and a mixture thereof. In order to improve the characteristics of the Schottky contact, it is preferred to perform Schottky annealing after forming the Schottky metal layer, and the temperature of the Schottky annealing is preferably 300° C. to 800° C., depending on the selected Schottky metal.

[0067] (6) If Figure 1 As shown, an anode metal layer 7 and an ohmic contact cathode metal layer 8 are formed on the surface of the Schottky metal layer and the first conductive type silicon carbide substrate layer by depositing metal, and then the ohmic contact cathode metal layer is laser annealed to form an ohmic contact. The anode metal layer is usually Al, and the ohmic contact cathode metal layer is usually Ti / Ni / Ag, which is used for conducting electricity and bonding and pressing wires during die packaging.

[0068] and Figure 7 Compared with the conventional junction barrier Schottky diode shown in the figure, the Figure 8 In the forward characteristics shown, the proposed trench junction barrier Schottky diode shows a lower forward voltage characteristic at the same active area, that is, 1.31V at 10A, and is preferentially turned on. At the same time, the trench junction barrier Schottky diode proposed in the present invention shows better reverse characteristics at the same active area, with the leakage current reduced by about 7 orders of magnitude at 1200V, and the breakdown capability increased by 14% at a leakage current reference level of 1e-4 A, as shown in FIG. Fig. 9 shown.

Claims

1. A method for preparing a silicon carbide trench junction barrier Schottky diode, characterized in that: The steps include: (1) preparing a silicon carbide substrate layer of a first conductivity type made of silicon carbide by in-situ growing a first epitaxial layer of the first conductivity type; (2) forming an ion implantation region of the second conductivity type in the first epitaxial layer of the first conductivity type by an ion implantation process; the upper surface of the ion implantation region is 0.2 μm away from the upper surface of the first epitaxial layer of the first conductivity type; (3) removing a 0.2 μm thick upper surface layer on the upper surface of the first epitaxial layer of the first conductivity type, and forming a second epitaxial layer of the first conductivity type on the upper surface of the first epitaxial layer of the first conductivity type by epitaxial growth; (4) forming a trench in the second epitaxial layer of the first conductivity type by dry plasma etching, wherein the bottom and corner of the trench extend deep into the ion implantation region of the second conductivity type; (5) forming a Schottky metal layer on the bottom and side of the trench and the upper surface of the second epitaxial layer of the first conductivity type by a sputtering deposition process; (6) forming an anode metal layer and an ohmic contact cathode metal layer on the surface of the Schottky metal layer and the first conductive type silicon carbide substrate layer respectively by depositing metal, and then laser annealing the ohmic contact cathode metal layer to form an ohmic contact.

2. The method for preparing a silicon carbide trench junction barrier Schottky diode according to claim 1, characterized in that: In step (5), after the Schottky metal layer is formed, Schottky annealing is performed, and the temperature of the Schottky annealing is 300° C. to 800° C.

3. The method for preparing a silicon carbide trench junction barrier Schottky diode according to claim 1, characterized in that: The silicon carbide trench junction barrier Schottky diode prepared in this way includes, from bottom to top, an ohmic contact cathode metal layer, a silicon carbide substrate layer of the first conductivity type, a first epitaxial layer of the first conductivity type, and a second epitaxial layer of the first conductivity type; A first epitaxial layer of the first conductivity type is ion-implanted on its surface to form a plurality of ion-implanted regions of the second conductivity type, and a second epitaxial layer of the first conductivity type above the ion-implanted regions of the second conductivity type is provided with grooves, the bottom and corners of the grooves being deep into the ion-implanted regions of the second conductivity type; The lateral width of the groove is smaller than the lateral width of the ion implantation region of the second conductivity type; A Schottky metal layer is provided on the second epitaxial layer of the first conductivity type, at the bottom of the trench and on the sidewalls of the trench, and an anode metal layer is provided on the Schottky metal layer.

4. The method for preparing a silicon carbide trench junction barrier Schottky diode according to claim 3, characterized in that: The doping concentration of the second epitaxial layer of the first conductivity type is greater than that of the first epitaxial layer of the first conductivity type. The thickness of the second epitaxial layer of the first conductivity type is 1-2 μm, and the doping concentration ranges from 1×10 16 cm -3 -1x10 17 cm -3 .

5. The method for preparing a silicon carbide trench junction barrier Schottky diode according to claim 3, characterized in that: The plurality of ion implantation regions of the second conductivity type in the first epitaxial layer of the first conductivity type have equal spacing, and the thickness of the ion implantation regions of the second conductivity type is 0.3-1 μm.

6. The method for preparing a silicon carbide trench junction barrier Schottky diode according to claim 3, characterized in that: The ions implanted into the second conductive type ion implantation region are boron ions or phosphorus ions.

7. The method for preparing a silicon carbide trench junction barrier Schottky diode according to claim 3, characterized in that: The ion implantation region of the second conductivity type has a Gaussian doping distribution, and the peak concentration is not less than 1x10 17 cm -3 .

8. The method for preparing a silicon carbide trench junction barrier Schottky diode according to claim 3, characterized in that: The first conductive type silicon carbide substrate layer is made of 4H-SiC, has a thickness of 300-350 μm, has a doping source of nitrogen or phosphorus, and has a low resistivity of 0.014-0.028 Ω∙cm.

9. The method for preparing a silicon carbide trench junction barrier Schottky diode according to claim 3, characterized in that: The material selection of the Schottky metal layer includes Ta, Co, Mo, Ti, Ni, Cr, Pt, Pd, Zr, W and mixtures of two or more thereof; the anode metal layer is Al, and the ohmic contact cathode metal layer is Ti / Ni / Ag.

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