Alternating wide and narrow mesa silicon carbide super junction schottky diode structure and preparation method

Abstract

This invention relates to the field of power device design technology, specifically to an alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure and its fabrication method. The diode has a first conductive mesa on its silicon carbide epitaxial layer. This first conductive mesa includes alternating first and second mesa, with the width of the first mesa being greater than that of the second mesa. The doping concentration of the P-type doped region on the first mesa decreases from the surface to the interior, while the P-type doping on the second mesa forms uniform doping due to scattering effects. This invention employs a periodically varying mesa width structure (alternating wide and narrow mesa). The wide mesa primarily handles current conduction, forming a low-resistance main current channel, while the narrow mesa primarily optimizes the electric field distribution and charge balance, enhancing the lateral depletion effect and improving the device's breakdown voltage. Furthermore, the ratio of the two mesa widths is adjustable; by adjusting the ratio of wide to narrow mesa according to application performance, optimized forward conduction performance and reverse breakdown voltage are obtained.

Description

Technical Field

[0001] This invention relates to the field of power device design technology, specifically to an alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure and its fabrication method. Background Technology

[0002] SiC, as a third-generation wide-bandgap semiconductor material, possesses excellent material properties such as a wide bandgap, high critical breakdown electric field, high electron saturation drift velocity, and high thermal conductivity, thus showing broad application prospects in high-voltage, high-frequency, and high-temperature power electronic devices. SiC unipolar devices have advantages such as high breakdown voltage, low specific on-resistance, high switching speed, and low switching losses. Significant progress has been made in this area through long-term research, with device performance gradually approaching the one-dimensional theoretical limit of SiC unipolar devices. However, breaking through the constraints of this one-dimensional theoretical limit and further reducing the specific on-resistance and conduction losses of SiC devices remains a major challenge for SiC power devices. Schottky diodes are fabricated using the metal-semiconductor junction principle formed by the contact between metal and semiconductor, resulting in a relatively low turn-on voltage.

[0003] Because Schottky diodes are single-carrier conducting devices, they suffer from a "silicon limit" problem between their breakdown voltage and forward resistance. To increase the breakdown voltage of a Schottky diode, the drift region thickness needs to be increased and / or the doping concentration in the drift region needs to be reduced. However, this inevitably leads to an increase in the forward voltage drop and forward conduction loss, thus limiting the application of Schottky diodes in high-voltage applications.

[0004] CN116864543A discloses a superjunction Schottky diode based on multilayer trench etching and its fabrication method, comprising: an ohmic contact cathode, an N+ substrate layer, an N-type silicon carbide epitaxial layer, at least one N-type silicon carbide epitaxial layer, and a Schottky contact anode arranged sequentially from bottom to top; the N-type silicon carbide epitaxial layer has a bottom trench; each N-type silicon carbide epitaxial layer has a trench, the trench extends from the trench opening to the bottom of the trench through the N-type silicon carbide epitaxial layer, the inner wall of the trench is on the same plane as the inner wall of the bottom trench, and the inner sidewalls of the trench and the bottom trench are covered with a first P-type ion implantation doped region; both the trench and the bottom trench are filled with a dielectric layer, the trench depth is 5-10 μm, and the deep trench structure is achieved by using shallow trenches, which improves the high voltage resistance of the device.

[0005] Superjunction technology was first applied in power MOS devices. It uses a series of alternating P-type and N-type doped regions as drift layers. Under reverse bias, the PN junction formed by the P-type and N-type doped regions is depleted, achieving mutual charge compensation. This enables the P-type and N-type regions to achieve high reverse breakdown voltage under high doping concentration, and their on-resistance is smaller. The application of superjunctions improves both the forward and reverse performance of Schottky diodes.

[0006] In existing technologies, silicon carbide superjunction Schottky barrier diodes fabricated using trench etching-sidewall ion implantation exhibit a breakdown voltage that is inversely proportional to the mesa width, while their on-resistance is directly proportional to the mesa width. For conventional superjunction Schottky diodes with uniform mesa widths, it is difficult to simultaneously achieve high breakdown voltage and low on-resistance. Furthermore, as the withstand voltage rating increases, the on-resistance increases rapidly and non-linearly. Additionally, uniform mesa superjunctions are prone to charge imbalances during manufacturing process fluctuations, leading to reduced breakdown voltage and uneven electric field distribution. This results in high requirements for process precision and significantly impacts yield. Summary of the Invention

[0007] To address the challenge that traditional uniform mesa structures struggle to balance low forward resistance and high reverse withstand voltage, this invention provides an alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure and fabrication method. This structure improves the electric field distribution under high reverse bias, optimizes charge balance and increases breakdown voltage, while the wide mesa provides a low-resistance current path for forward conduction, reducing the overall on-resistance of the device and achieving a high-performance device structure. Furthermore, the structural design itself offers better tolerance to process variations.

[0008] This invention is achieved through the following technical solution:

[0009] An alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure includes a silicon carbide substrate layer, a silicon carbide epitaxial layer disposed on the silicon carbide substrate layer, and the silicon carbide epitaxial layer being doped with N-type.

[0010] Multiple inclined trenches are etched on the silicon carbide epitaxial layer, and P-type doped regions are set on the sidewalls of the trenches to form a second conductive P-type pillar region.

[0011] The trench is filled with an insulating medium;

[0012] The first conductive structure mesa of the silicon carbide epitaxial layer includes alternating first mesa and second mesa, wherein the width of the first mesa is greater than the width of the second mesa.

[0013] The doping concentration of the P-type doped region on the first mesa decreases from the surface to the interior, while the P-type doping on the second mesa can form uniform doping due to the scattering effect.

[0014] A Schottky metal layer is disposed on the silicon carbide epitaxial layer.

[0015] Preferably, the width of the first tabletop and the width of the second tabletop are adjusted according to the application performance, and the width of the first tabletop and the width of the second tabletop are 2~5μm.

[0016] Preferably, the ratio of the number of the first countertop to the number of the second countertop is between 1:1 and 5:1.

[0017] Preferably, the thickness of the silicon carbide epitaxial layer is 5~20 μm, and the doping concentration is 2. 10 14 ~6 10 16 cm -3 .

[0018] Preferably, the inclination angle θ of the trench is in the range of 80°~90°.

[0019] Preferably, the doping concentration gradient of the second conductive P-type pillar region varies along the depth direction, with the doping concentration near the Schottky metal layer being higher than that far from the Schottky metal layer.

[0020] Preferably, the doping depth of the second conductive P-type pillar region is 0.2~0.4 μm, and the doping concentration is 2. 10 15 ~6 10 17 cm -3 .

[0021] Preferably, the insulating medium is silicon dioxide.

[0022] Preferably, the Schottky metal layer is made of at least one metal selected from titanium, nickel, or platinum, or an alloy thereof.

[0023] A method for fabricating an alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure includes:

[0024] S1, Preparation of silicon carbide substrate;

[0025] S2, an epitaxial layer Nepi is epitaxially grown on a silicon carbide substrate to form a silicon carbide epitaxial layer;

[0026] S3, deposit a SiO2 layer on the surface of the silicon carbide epitaxial layer as a mask for "trench etching-sidewall ion implantation";

[0027] S4, perform SiO2 etching and SiC trench etching;

[0028] S5, perform P-type ion implantation on the trench sidewall and then perform high-temperature annealing activation treatment;

[0029] S6 introduces Al ions to form a superjunction P-pillar.

[0030] S7, remove the SiO2 mask.

[0031] S8, using SiO2 for trench backfilling;

[0032] S9 involves depositing metallic nickel on the back side of a silicon carbide substrate and annealing it to form an ohmic contact between the Ni and the SiC substrate, serving as the device cathode; and sputtering metallic nickel on the front side of a silicon carbide epitaxial layer, which naturally forms a Schottky contact with the SiC, serving as the device anode.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] This invention discloses an alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure. The structure employs a periodically varying mesa width (alternating wide and narrow mesa). The wide mesa primarily handles current conduction, forming a low-resistance main current channel, while the narrow mesa optimizes the electric field distribution and charge balance, enhancing the lateral depletion effect and improving the device's breakdown voltage. Secondly, the ratio of the two mesa widths is adjustable; adjusting the ratio according to application performance yields optimized forward conduction and reverse breakdown voltage. Thirdly, due to the alternating wide and narrow mesa structure, the P-type doped region in the wide mesa exhibits a gradually decreasing doping concentration from the surface to the interior, while the P-type doped region in the narrow mesa maintains a uniform high doping concentration due to scattering effects. This allows for a natural gradient change in the electric field distribution, resulting in a more uniform electric field distribution. Finally, this process method allows for more lenient photolithography precision, is compatible with current superjunction manufacturing technologies, has higher tolerance for process fluctuations, and is less sensitive to deviations in trench etching and ion implantation processes, thus improving device yield. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of an alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure according to the present invention;

[0036] Figure 2 This is a flowchart illustrating the fabrication process of an alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure according to the present invention.

[0037] Figure 3 The diagram shows silicon carbide superjunction Schottky diodes with different mesa types; where a represents a single mesa type; b represents a single narrow mesa type; and c represents alternating wide and narrow mesa types.

[0038] Figure 4 Forward conduction curves of silicon carbide superjunction Schottky diodes with different mesa types.

[0039] In the figure, 101 is the silicon carbide substrate; 102 is the silicon carbide epitaxial layer; 103 is the trench; 104 is the doped region; 105 is the backfill dielectric layer; 106 is the cathode; 107 is the second mesa; 108 is the first mesa; and 109 is the Schottky metal layer. Detailed Implementation

[0040] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0041] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0042] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0043] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0044] This invention discloses an alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure, comprising:

[0045] A silicon carbide substrate 101 is provided, and a silicon carbide epitaxial layer 102 with a thickness of 5~20μm and a doping concentration of 2 is disposed on the silicon carbide substrate 101. 10 14 ~6 10 16 cm -3 Furthermore, a silicon carbide epitaxial layer 102 with a thickness of 12~18μm can be selected, and the silicon carbide epitaxial layer 102 is doped with N-type, with a doping concentration of 2~6. 10 16 cm -3 .

[0046] Multiple inclined trenches 103 are etched on the silicon carbide epitaxial layer 102. The depth of the trenches 103 is 5~20μm, and the inclination angle θ of the trenches 103 is in the range of 80°~90°. Preferably, the depth of the trenches 103 is 10~15μm, and the inclination angle θ is 80~85°.

[0047] The sidewalls of trench 103 are doped with P-type magnets to form a second conductive P-type pillar region. The doping depth of the second conductive P-type pillar region is 0.2~0.4μm, and the doping concentration is 2. 10 15 ~6 1017 cm -3 Furthermore, the doping concentration ranges from 1.5 to 3. 10 17 cm -3 .

[0048] The doping concentration gradient of the second conductive P-type pillar region varies along the depth direction, with the doping concentration near the Schottky metal layer 109 being higher than that far from the Schottky metal layer 109.

[0049] The trench 103 is filled with a backfill medium layer 105, which is made of silicon dioxide.

[0050] The first conductive structure mesa of the silicon carbide epitaxial layer 102 includes alternating first mesa 108 and second mesa 107. The width of the first mesa 108 is greater than the width of the second mesa 107. The width of the first mesa 108 and the width of the second mesa 107 are adjusted according to the application performance. The width of the first mesa 108 and the width of the second mesa 107 are 2~5μm.

[0051] The ratio of the number of the first tabletop 108 to the number of the second tabletop 107 ranges from 1:1 to 5:1.

[0052] The doping concentration of the P-type doped region on the first mesa 108 decreases from the surface to the interior, while the P-type doped region on the second mesa 107 can form uniform doping due to the scattering effect.

[0053] A Schottky metal layer 109 is disposed on the silicon carbide epitaxial layer 102, and the Schottky metal layer 109 is made of at least one metal selected from titanium, nickel or platinum or an alloy thereof.

[0054] This invention also discloses a method for fabricating an alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure, comprising:

[0055] S1, Silicon carbide substrate 101 is prepared;

[0056] S2, an epitaxial layer Nepi is epitaxially grown on the silicon carbide substrate 101 to form a silicon carbide epitaxial layer 102;

[0057] S3, deposit a SiO2 layer on the surface of the silicon carbide epitaxial layer 102 as a "trench etching-sidewall ion implantation" mask;

[0058] S4, perform SiO2 etching and SiC trench 103 etching;

[0059] S5, perform P-type ion implantation on the sidewall of trench 103, and then perform high-temperature annealing activation treatment;

[0060] S6 introduces Al ions to form a superjunction P-pillar.

[0061] S7, remove the SiO2 mask.

[0062] S8, SiO2 is used for backfilling the medium in trench 103;

[0063] S9, metallic nickel is deposited on the back side of silicon carbide substrate 101 and annealed to form an ohmic contact between Ni and SiC substrate, serving as device cathode 106; metallic nickel is sputtered on the front side of silicon carbide epitaxial layer 102, naturally forming a Schottky contact with SiC to serve as device anode.

[0064] Example 1

[0065] An alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure is disclosed, wherein the silicon carbide substrate 101 has a thickness of 1.5 μm, is N-type doped, and has a doping concentration of 5%. 10 18 cm -3 The silicon carbide epitaxial layer 102 has a thickness of 12 μm, is N-type doped, and has a doping concentration of 2~6. 10 16 cm -3 Trench 103 is etched from the silicon carbide epitaxial layer 102 to a depth of 10-15 μm at an etching angle of 80-85°, leaving a 2 μm etching margin. Ion implantation is then performed on the sidewalls of trench 103 to create doped regions 104. The doping type is P-type, the doping width is 0.2 μm, and the doping concentration is 1.5%. 10 17 cm -3 The trench 103 is filled with a backfill medium layer 105, which is made of silicon dioxide.

[0066] Table 1. Breakdown voltage, forward ratio on-resistance, and power figure of merit for different silicon carbide superjunctions.

[0067]

[0068] As can be seen from Table 1, compared with a superjunction Schottky diode with a single mesa width, the embodiments of the present invention have a higher breakdown voltage but also a larger forward resistance when using a narrow mesa (i.e., the width of the second mesa is 2μm), and a lower breakdown voltage but also a smaller forward resistance when using a wide mesa (i.e., the width of the first mesa is 5μm). When using alternating wide and narrow mesa (i.e., the number of mesa widths of 2μm and 5μm is in a 1:1 ratio), the breakdown voltage is slightly lower than that of a single narrow mesa, but the forward resistance is also smaller, and the power performance is improved.

[0069] Figure 4This invention provides an alternating wide and narrow mesa superjunction Schottky diode structure and an IV curve for forward conduction of a superjunction Schottky diode based on a single mesa width. It can be seen that the embodiment of this invention has a lower forward specific on-resistance, the best power figure of merit, and improved device performance.

[0070] When the device is in the reverse state, the N-pillars and P-pillars in the drift region deplete each other (lateral depletion). This requires the superjunction structure to satisfy the charge balance principle, i.e., the product of the N-pillar impurity concentration and the P-pillar impurity concentration with their respective widths must be equal, and the positive and negative fixed charges must cancel each other out. Due to the simultaneous presence of longitudinal Schottky contact depletion and lateral depletion, the electric field distribution of the superjunction becomes a rectangular distribution, making the breakdown voltage almost linearly related to the doping concentration. The breakdown voltage decreases as the doping concentration increases. When the electric field strength exceeds the critical breakdown electric field Ec=2 of SiC... 10 6 V / cm, device breakdown. However, in reality, achieving charge balance is difficult due to the limitations of actual manufacturing processes. Furthermore, the superjunctions fabricated using trench etching technology have a trapezoidal P-N structure, narrower at the top and wider at the bottom, making charge balance even more challenging. The wider mesa width (first mesa) exacerbates the charge imbalance between the upper and lower layers of the superjunction, leading to a decrease in breakdown voltage. While a narrower mesa width (second mesa) makes charge balance easier to achieve, it reduces the forward conduction area, increasing the forward resistance and decreasing forward conduction performance. Therefore, a method using... Figure 2 The alternating wide and narrow mesa superjunction Schottky diode structure shown in the diagram better solves the problem that a single mesa structure cannot simultaneously achieve forward conduction and reverse voltage withstand, thus optimizing device performance.

[0071] For superjunction structures, breakdown typically occurs in the middle of the P-pillars and N-pillars. When breakdown occurs in the middle of the N-pillar, the lateral electric field distribution is uniform, and the total electric field strength is equal to the longitudinal electric field strength. Therefore, the electric field in the middle of the N-pillar is crucial for studying superjunction breakdown. When the device is forward-biased, the anode is connected positively, and current flows through the Schottky contact, through the drift region (N-pillar), and to the substrate. Only the N-pillar participates in conduction; that is, compared to a traditional Schottky diode, the effective conduction area of ​​the drift region is halved, resulting in a larger specific on-resistance. To achieve the same specific on-resistance as a traditional Schottky diode, the N-pillar doping concentration needs to be increased by about two times, or an order of magnitude, to 1. 10 16 ~1 10 17 cm -3 Similar to traditional Schottky barrier diodes, the forward on-resistance decreases with increasing doping concentration. Figure 4 The graph shows the forward conduction curve of the device, thus indicating that the superjunction device fabricated using alternating wide and narrow mesa patterns, under the combined effect, is effective. Figure 3 (c) The structure is different from the traditional single-roof structure Figure 3 Compared to (a) and (b), this structure can significantly improve the forward conduction performance of the device while maintaining the breakdown voltage at the same level, thereby improving the overall performance of the device.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A silicon carbide superjunction Schottky diode structure with alternating wide and narrow mesa planar surfaces, characterized in that, It includes a silicon carbide substrate (101), a silicon carbide epitaxial layer (102) disposed on the silicon carbide substrate (101), and the silicon carbide epitaxial layer (102) is doped with N-type; Multiple inclined trenches (103) are etched on the silicon carbide epitaxial layer (102). The sidewalls of the trenches (103) are provided with doped P-type doped regions (104) formed by ion implantation, forming a second conductive P-type pillar region. The opening of the trenches (103) is wider at the top and narrower at the bottom. The trench (103) is filled with a backfill medium layer (105); The upper surface of the silicon carbide epitaxial layer (102) is divided by trenches (103) into alternating first mesa (108) and second mesa (107), the width of the first mesa (108) being greater than the width of the second mesa (107). The doping concentration of the P-type doped region on the first mesa (108) decreases from the surface to the interior, while the P-type doping on the second mesa (107) forms a uniform doping due to the scattering effect. A Schottky metal layer (109) is disposed on the silicon carbide epitaxial layer (102).

2. The alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure according to claim 1, characterized in that, The table width of the first table (108) and the table width of the second table (107) are adjusted according to the application performance, and the table width of the first table (108) and the second table (107) is 2~5μm.

3. The alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure according to claim 1, characterized in that, The ratio of the number of the first tabletop (108) to the number of the second tabletop (107) ranges from 1:1 to 5:

1.

4. The alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure according to claim 1, characterized in that, The thickness of the silicon carbide epitaxial layer (102) is 5~20 μm, and the doping concentration is 2. 10 14 ~6 10 16 cm -3 .

5. The alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure according to claim 1, characterized in that, The depth of the trench (103) is 5~20μm, and the tilt angle θ of the trench (103) is in the range of 80°~90°.

6. The alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure according to claim 1, characterized in that, The doping depth of the second conductive P-type pillar region is 0.2~0.4μm, and the doping concentration is 2. 10 15 ~6 10 17 cm -3 .

7. The alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure according to claim 1, characterized in that, The backfill medium layer (105) is made of silicon dioxide.

8. The alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure according to claim 1, characterized in that, The Schottky metal layer (109) is made of at least one metal selected from titanium, nickel or platinum or an alloy thereof.

9. A method for fabricating an alternating wide and narrow mesa silicon carbide superjunction Schottky diode structure as described in any one of claims 1 to 8, characterized in that, include: a. Preparation of silicon carbide substrate (101); b. An epitaxial layer is grown on the silicon carbide substrate (101) to form a silicon carbide epitaxial layer (102); a SiO2 layer is deposited on the surface of the silicon carbide epitaxial layer (102) as a "trench etching-sidewall ion implantation" mask. c. Perform SiO2 etching and SiC trench etching; d. Perform P-type ion implantation on the sidewall of trench (103) and perform high-temperature annealing activation treatment; e. Introducing Al ions to form a superjunction P-pillar; f, Remove the SiO2 mask; g, SiO2 is used for medium backfilling of trench (103); h, metallic nickel is deposited on the back side of the silicon carbide substrate (101) and annealed to form an ohmic contact between Ni and the SiC substrate, serving as the device cathode (106); metallic nickel is sputtered on the front side of the silicon carbide epitaxial layer (102), naturally forming a Schottky contact with SiC, serving as the device anode.

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