Composite Schottky diode device with barrier modulation

Abstract

The invention relates to the technical field of power semiconductor devices, in particular to a composite Schottky diode device with barrier modulation, which comprises an N + substrate; an N-drift epitaxial layer formed on the N + substrate; the groove structures are formed in the N-drift epitaxial layer, and gate dielectric layers and field plates are arranged in the groove structures; the Schottky metal electrode is formed on the surface of the N-drift epitaxial layer; the central Schottky main conduction region is located in an N-drift epitaxial layer region between two adjacent groove structures, and the Schottky metal electrode is in direct contact with the N-drift epitaxial layer not doped with the P-type impurities to form a low-barrier Schottky junction; the edge P-barrier modulation region is formed below the surface of the N-drift epitaxial layer and is adjacent to the region of the groove structure, the Schottky metal electrode is only in contact with the edge P-barrier modulation region in the edge region, an equivalent high-barrier Schottky junction is formed, and the balance of low forward voltage drop, low reverse electric leakage and high surge current capacity is achieved.

Description

Technical Field

[0001] This invention relates to the field of power semiconductor device technology, and more particularly to a composite Schottky diode device with barrier modulation. Background Technology

[0002] Schottky barrier diodes (SBDs) are widely used in secondary-side rectification of switching power supplies, DC / DC converters, on-board chargers (OBCs), motor drives, and various industrial power supplies due to their advantages such as low forward voltage drop, short reverse recovery time, and low switching losses. For medium-to-low voltage applications (40–200 V), devices typically need to simultaneously meet the following requirements: low forward voltage drop (VF), low reverse leakage current (IR), a certain reverse withstand voltage margin, and high non-repeating surge current capability.

[0003] To reduce leakage current and improve breakdown voltage, the industry has proposed trench-type Schottky diodes. This structure involves etching longitudinal trenches in an N-type drift epitaxial layer, forming a gate dielectric and a polysilicon or metal field plate within the trench, which is then connected to the anode potential or reference potential. The trench field plate redistributes the surface electric field through capacitive coupling, reducing the peak electric field near the main junction and allowing for a suitable increase in epitaxial layer doping. This, in turn, reduces on-resistance and reverse leakage current while maintaining a certain breakdown voltage.

[0004] Current research suggests using metals with different barrier heights within the same rectifier device. For example, high-barrier metals (such as Ni and Pt) can be used in the active region to suppress leakage current and improve edge electric field distribution. Other techniques involve filling trenches with doped polysilicon and performing solid-state diffusion to form P- or N-regions on the trench sidewalls and bottom, achieving electric field shielding and surge enhancement effects similar to junction barrier Schottky diodes (JBS) or merged PIN Schottky diodes (MPS).

[0005] To address the issue of high breakdown voltage in trench Schottky diodes, the 2011 ISPSD paper "Innovative Designs Enable 300-VTMBS with Ultra-low On-state Voltage and Fast Switching Speed" proposed using P-doping technology to adjust the height of the Schottky barrier, raising the effective barrier on top of the original metal barrier, thereby achieving a breakdown voltage of over 300 V and low leakage current.

[0006] Although the trench-type Schottky diodes and related improved structures have achieved certain results in improving voltage withstand and reducing leakage current, the existing technology still has the following shortcomings for medium and low voltage applications of 40-200 V:

[0007] (1) The 2011 ISPSD paper introduced P doping into the trench Schottky structure to adjust the barrier height of the Schottky interface, which is equivalent to "raising" the effective barrier on the basis of the original metal barrier, thereby achieving a withstand voltage of over 300 V and a low leakage current. However, this kind of scheme to raise the barrier by P doping is essentially sacrificing some forward conduction performance in exchange for high withstand voltage and low leakage current. Its forward conduction voltage drop is relatively high, which is not ideal for 40-200V medium and low voltage rectification applications that value conduction loss and efficiency more.

[0008] (2) Existing technologies suppress leakage current and improve edge electric field distribution by introducing high barrier metals (such as Ni and Pt) into the active region, or fill the trench with doped polysilicon and form P / N regions through solid-state diffusion to achieve electric field shielding and surge enhancement similar to JBS / MPS. Although such structures can reduce reverse leakage current and improve breakdown voltage, they usually bring the following trade-offs: the overall effective barrier of the active region is increased or the PN path participates in conduction, making it difficult to reduce VF to the level of a pure low barrier trench Schottky diode (TMBS).

[0009] (3) Bimetallic barrier structures require multiple metal materials and additional metal patterning steps, which place high demands on the stability of the metal-silicon interface, intermetallic diffusion, and annealing conditions. The process is complex and detrimental to mass production consistency. P-doped solid-phase diffusion in the trench also requires precise control of diffusion depth and lateral expansion, resulting in a narrow process window and difficulty in batch consistency control. For mass production lines of medium and low voltage products, these solutions have certain limitations in terms of process cost and manufacturability.

[0010] Therefore, existing trench Schottky diodes suffer from several problems: difficulty in simultaneously achieving low leakage current, low VF, and high surge capability; reverse leakage current and current concentration are mainly dominated by the low barrier region, especially the trench edge and shallow surface region; excessive current concentration near the surface and trench under large surge conditions, resulting in insufficient utilization of the deep silicon mass and affecting surge capability and interface reliability; and a lack of composite trench structures with relatively simple structure and fabrication that can achieve multi-region barrier modulation laterally. There is an urgent need for a trench-type Schottky barrier diode structure suitable for medium and low voltage rectification, achieving comprehensive optimization of forward conduction, reverse shielding, and surge current conduction. Summary of the Invention

[0011] In view of this, in order to overcome the shortcomings of the prior art, the present invention provides a composite Schottky diode device with barrier modulation. While retaining a single low-barrier Schottky metal and the existing TMBS process, multiple functional regions are constructed laterally through composite trenches and doping modulation. A balance between low forward voltage drop, low reverse leakage current and high surge current capability is achieved through lateral P-barrier modulation.

[0012] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0013] This invention provides a composite Schottky diode device with barrier modulation, comprising:

[0014] An N+ substrate is used to provide an ohmic cathode contact;

[0015] An N-drift epitaxial layer formed on the N+ substrate;

[0016] At least two trench structures are formed in the N-drift epitaxial layer, wherein the trench structures have a gate dielectric layer and a field plate;

[0017] A Schottky metal electrode is formed on the surface of the N-drift epitaxial layer, the Schottky metal electrode being composed of a single low-barrier metal material;

[0018] A central Schottky dominant pass region is located in the N-drift epitaxial layer region between two adjacent trench structures, wherein the Schottky metal electrode is in direct contact with the N-drift epitaxial layer without P-type impurities to form a low-barrier Schottky junction;

[0019] And an edge P-barrier modulation region, formed below the surface of the N-drift epitaxial layer and adjacent to the trench structure, wherein the Schottky metal electrode in the edge region only contacts the edge P-barrier modulation region to form an equivalent high-barrier Schottky junction;

[0020] The edge P-barrier modulation region is adjacent to the N-drift epitaxial layer region without P-type impurities in the lateral direction, so that the edge of the N-drift epitaxial layer forms a barrier modulation shielding region.

[0021] As a further embodiment of the present invention, the trench structure comprises etching at least two longitudinal trenches extending along the current flow direction on the surface of the N-drift epitaxial layer, wherein a gate dielectric layer is formed on the sidewalls and bottom of the longitudinal trenches, and the interior of the longitudinal trenches is filled with polysilicon or a metal field plate, and is connected to the anode potential or reference potential through a conductive layer composed of polysilicon or a metal field plate, for shielding the electric field and improving the electric field distribution; wherein the gate dielectric layer is SiO2 or a composite dielectric.

[0022] As a further embodiment of the present invention, the Schottky metal electrode is a continuous metal layer formed on the surface of the N-drift epitaxial layer, and contacts the N-drift epitaxial layer through an opening facing the surface of the N-drift epitaxial layer.

[0023] As a further aspect of the present invention, the metal material of the Schottky metal electrode is a stack composed of one or more of Ti, Ni, Mo, and W.

[0024] As a further aspect of the present invention, the low-barrier Schottky junction serves as the main current path for forward conduction of the device.

[0025] As a further aspect of the present invention, in the edge region near the trench structure, a lightly doped P-region is introduced below the surface of the N-drift epitaxial layer in the edge P-barrier modulation region, and the doping concentration of the edge P-barrier modulation region is 2 to 20 times that of the doping concentration of the N-drift epitaxial layer.

[0026] As a further aspect of the present invention, the junction depth of the edge P-barrier modulation region is less than the depth of the trench structure.

[0027] As a further aspect of the present invention, the depth of the upper boundary of the edge P-barrier modulation region from the surface of the N-drift epitaxial layer is 0.1 μm to 0.5 μm.

[0028] As a further aspect of the present invention, the junction depth of the edge P-barrier modulation region is 0.3 μm to 1.0 μm.

[0029] As a further aspect of the present invention, the width of the edge P-barrier modulation region is configured to adjust the area ratio of the central Schottky dominant pass region to the edge P-barrier modulation region in order to optimize the forward voltage drop VF of the device.

[0030] As a further aspect of the present invention, a termination structure is provided around the device of the composite Schottky diode device, the termination structure including one or more of a P-type termination ring, a field plate termination, or a field oxide termination.

[0031] Compared with the prior art, the composite Schottky diode device with barrier modulation provided by the present invention has the following beneficial effects:

[0032] 1. This invention achieves synergistic optimization of low forward voltage drop, low reverse leakage current, and high withstand voltage by maintaining a pure low-barrier Schottky junction in the central Schottky-dominant pass region between the two trenches. During forward conduction, current preferentially and primarily flows through this low-barrier region. Since this region is the dominant pass channel and is not p-type doped to raise the barrier, the overall forward voltage drop of the device is maintained at an excellent level close to that of an ideal low-barrier trench Schottky diode, directly reducing the device's conduction losses, improving power conversion efficiency, and significantly reducing the forward voltage drop.

[0033] 2. Under reverse bias conditions, the P-barrier modulation region near the trench edge can effectively suppress reverse leakage current (IR) and improve breakdown voltage. The PN junction formed by the P-region and N-drift region will deplete first, and its depletion layer will extend laterally towards the central low-barrier region, producing a "pinch-off" effect, thereby significantly reducing the effective low-barrier Schottky area that is prone to high leakage current. At the same time, the high electric field is transferred from the sensitive metal-semiconductor interface to the PN junction and deep trench field plate in the bulk, reducing the electric field peak at the interface, thereby greatly suppressing tunneling leakage current and thermionic emission leakage current. Combined with the electric field modulation effect of the trench field plate, the device achieves low leakage current while also improving the breakdown voltage and providing a more sufficient withstand voltage margin.

[0034] 3. Under extreme conditions of large surge currents, the structural advantages of the composite Schottky diode device of this invention are fully demonstrated, with current still primarily injected through the central low-barrier region. The P-barrier modulation region and the trench field plate work together to suppress the current accumulation effect at the Schottky interface edge, forcing the current to spread more uniformly in the N-drift layer both vertically and laterally. This allows the bulk region of the semiconductor material to be utilized more effectively to carry large currents, avoiding local overheating, thereby significantly improving the surge current capacity and IL of the device. 2 The t-value enhances the system's reliability under abnormal operating conditions and significantly improves the non-recurring surge current (It). FSM (Tolerance)

[0035] 4. This invention reduces the electric field strength at the Schottky interface during reverse bias and the current concentration during surges, thereby alleviating interface stress, which helps to delay device degradation and extend its service life. During fabrication, the P-barrier modulation region can be formed via ion implantation, and the implantation mask of the device's terminal guard ring can be reused, eliminating the need for additional photolithography steps. Utilizing the synergistic mechanism of central low-barrier conduction and edge P-region modulation, a comprehensive optimization of low forward voltage drop, low reverse leakage current, high breakdown voltage, and high surge capability can be simultaneously achieved.

[0036] These or other aspects of the invention will become more apparent from the following description of embodiments. It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. In the drawings:

[0038] Figure 1 This is a schematic diagram of the structure of a composite Schottky diode device with barrier modulation according to the present invention.

[0039] Figure label:

[0040] 10-N+ substrate, 11-N-drift epitaxial layer, 12-edge P-barrier modulation region, 20-gate dielectric layer, 30-field plate, 40-Schottky metal electrode. Detailed Implementation

[0041] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0042] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0043] See Figure 1 As shown, an embodiment of this application provides a composite Schottky diode device with barrier modulation, comprising:

[0044] An N+ substrate 10 is used to provide an ohmic cathode contact;

[0045] An N-drift epitaxial layer 11 is formed on the N+ substrate 10;

[0046] At least two trench structures are formed in the N-drift epitaxial layer 11, wherein the trench structures have a gate dielectric layer 20 and a field plate 30;

[0047] A Schottky metal electrode 40 is formed on the surface of the N-drift epitaxial layer 11, the Schottky metal electrode 40 being made of a single low-barrier metal material;

[0048] A central Schottky dominant pass region is located in the N-drift epitaxial layer 11 region between two adjacent trench structures, wherein the Schottky metal electrode 40 is in direct contact with the N-drift epitaxial layer 11 without P-type impurities to form a low-barrier Schottky junction, which serves as the main current path for forward conduction of the device.

[0049] And an edge P-barrier modulation region 12, formed in the region below the surface of the N-drift epitaxial layer 11 and adjacent to the trench structure, wherein the Schottky metal electrode 40 contacts only the edge P-barrier modulation region 12 in the edge region to form an equivalent high-barrier Schottky junction.

[0050] The edge P-barrier modulation region 12 is adjacent to the region of the N-drift epitaxial layer 11 that is not doped with P-type impurities in the lateral direction, so that the edge of the N-drift epitaxial layer 11 forms a barrier modulation shielding region.

[0051] See Figure 1 As shown, the trench structure consists of at least two longitudinal trenches extending along the current flow direction etched on the surface of the N-drift epitaxial layer 11. The sidewalls and bottom of the longitudinal trenches form a gate dielectric layer 20. The interior of the longitudinal trenches is filled with polysilicon or a metal field plate and connected to the anode potential or reference potential through a conductive layer composed of polysilicon or a metal field plate, for shielding the electric field and improving the electric field distribution. The gate dielectric layer 20 is SiO2 or a composite dielectric.

[0052] In this embodiment, the Schottky metal electrode 40 is a continuous metal layer formed on the surface of the N-drift epitaxial layer 11, and contacts the N-drift epitaxial layer 11 through an opening facing the surface of the N-drift epitaxial layer 11; wherein, the metal material of the Schottky metal electrode 40 is a stack composed of one or more of Ti, Ni, Mo, and W.

[0053] In this embodiment, a lightly doped P-region is introduced below the surface of the N-drift epitaxial layer 11 in the edge region near the trench structure P-barrier modulation region 12. The doping concentration of the edge P-barrier modulation region 12 is 2 to 20 times that of the N-drift epitaxial layer 11. The doping concentration of the N-drift epitaxial layer 11 is (0.5–5) × 10⁻⁶. 16 cm -3 The thickness is designed according to the rated withstand voltage of the device.

[0054] The junction depth of the edge P-barrier modulation region 12 is less than the depth of the trench structure. The upper boundary of the edge P-barrier modulation region 12 is 0.1 μm to 0.5 μm from the surface of the N-drift epitaxial layer 11. The junction depth of the edge P-barrier modulation region 12 is 0.3 μm to 1.0 μm.

[0055] In this embodiment, the width of the edge P-barrier modulation region 12 is configured to adjust the area ratio of the central Schottky dominant pass region to the edge P-barrier modulation region 12 in order to optimize the forward voltage drop VF of the device.

[0056] In some embodiments, a termination structure is further provided around the composite Schottky diode device. The termination structure includes one or more of a P-type termination ring, a field plate termination, or a field oxygen termination to further optimize the edge electric field distribution.

[0057] When conducting with a small forward current, the central low-barrier Schottky junction has the lowest potential and conducts first. The current mainly flows into the N-drift epitaxial layer 11 from the central Schottky-dominated conduction region. The edge P-barrier modulation region 12 has a higher barrier and a smaller area, so the forward current accounts for a lower proportion and has a limited impact on the overall forward voltage drop VF. The device maintains a forward voltage drop close to that of a low-barrier trench Schottky diode within the rated forward operating current range.

[0058] Under the action of reverse voltage, the P-barrier modulation region 12 near the edge of the trench structure first forms a depletion region at the P- / N-junction. The depletion region extends laterally below the central low-barrier Schottky, achieving local pinch-off and reducing the effective low-barrier Schottky area. At the same time, the high field moves from the Schottky interface to the interior of the P- / N-junction and the depth of the trench, which helps to reduce the electric field peak and leakage current near the Schottky interface. Combined with the electric field redistribution effect of the trench field plate 30, the overall reverse leakage current can be significantly reduced and the device breakdown voltage can be improved.

[0059] Under large surge forward current conditions, the current preferentially enters the N-drift epitaxial layer 11 through the central Schottky dominant pass region. The edge P-barrier modulation region 12 and the field plate 30 of the trench structure suppress the current concentration effect at the trench edge and guide the current to extend deeper and laterally in the N-drift epitaxial layer 11, effectively utilizing more deep silicon to carry the current, reducing hot spot temperature rise, and improving the non-repeating surge current I. FSM and I 2 t capacity.

[0060] In the composite trench Schottky diode device with barrier modulation proposed in this invention, the process of the edge P-barrier modulation region 12 is compatible with existing TMBS manufacturing processes, allowing reuse of existing P-injection masks without requiring additional photolithography processes. The composite Schottky barrier diode with barrier modulation proposed in this invention adds a lateral P-barrier modulation structure to a single Schottky metal. The width of the edge P-barrier modulation region 12 in the composite Schottky barrier diode structure proposed in this invention determines the proportion of low-barrier and high-barrier regions; the wider the edge P-barrier modulation region 12, the more low-barrier regions there are, and the lower the forward voltage drop of the device.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite Schottky diode device with barrier modulation, characterized in that, include: An N+ substrate (10) is used to provide an ohmic cathode contact; An N-drift epitaxial layer (11) is formed on the N+ substrate (10). At least two trench structures are formed in the N-drift epitaxial layer (11), wherein the trench structures have a gate dielectric layer (20) and a field plate (30). A Schottky metal electrode (40) is formed on the surface of the N-drift epitaxial layer (11), the Schottky metal electrode (40) being made of a single low-barrier metal material; A central Schottky dominant pass region is located in the N-drift epitaxial layer (11) region between two adjacent trench structures, wherein the Schottky metal electrode (40) is in direct contact with the N-drift epitaxial layer (11) without P-type impurities to form a low-barrier Schottky junction; And an edge P-barrier modulation region (12), formed below the surface of the N-drift epitaxial layer (11) and adjacent to the trench structure, wherein the Schottky metal electrode (40) is in contact with the edge P-barrier modulation region (12) only in the edge region to form an equivalent high-barrier Schottky junction; The edge P-barrier modulation region (12) is adjacent to the region of the N-drift epitaxial layer (11) without P-type impurities in the lateral direction, so that the edge of the N-drift epitaxial layer (11) forms a barrier modulation shielding region.

2. The composite Schottky diode device with barrier modulation as described in claim 1, characterized in that, The trench structure consists of at least two longitudinal trenches extending along the current flow direction etched on the surface of the N-drift epitaxial layer (11). The sidewalls and bottom of the longitudinal trenches form a gate dielectric layer (20). The interior of the longitudinal trenches is filled with polysilicon or a metal field plate and connected to the anode potential or reference potential through a conductive layer composed of polysilicon or a metal field plate, for shielding the electric field and improving the electric field distribution. The gate dielectric layer (20) is SiO2 or a composite dielectric.

3. The composite Schottky diode device with barrier modulation as described in claim 1, characterized in that, The Schottky metal electrode (40) is a continuous metal layer formed on the surface of the N-drift epitaxial layer (11) and contacts the N-drift epitaxial layer (11) through an opening facing the surface of the N-drift epitaxial layer (11).

4. The composite Schottky diode device with barrier modulation as described in claim 3, characterized in that, The Schottky metal electrode (40) is a stack of one or more of Ti, Ni, Mo, and W.

5. The composite Schottky diode device with barrier modulation as described in claim 1, characterized in that, In the edge region near the trench structure, an edge P-barrier modulation region (12) is introduced with a lightly doped P-region below the surface of the N-drift epitaxial layer (11), and the doping concentration of the edge P-barrier modulation region (12) is 2 to 20 times that of the doping concentration of the N-drift epitaxial layer (11).

6. The composite Schottky diode device with barrier modulation as described in claim 5, characterized in that, The junction depth of the edge P-barrier modulation region (12) is less than the depth of the trench structure.

7. The composite Schottky diode device with barrier modulation as described in claim 6, characterized in that, The upper boundary of the edge P-barrier modulation region (12) is 0.1 μm to 0.5 μm from the surface of the N-drift epitaxial layer (11).

8. The composite Schottky diode device with barrier modulation as described in claim 7, characterized in that, The junction depth of the edge P-barrier modulation region (12) is 0.3 μm to 1.0 μm.

9. The composite Schottky diode device with barrier modulation as described in claim 8, characterized in that, The width of the edge P-barrier modulation region (12) is configured to adjust the area ratio of the central Schottky dominant pass region to the edge P-barrier modulation region (12).

10. The composite Schottky diode device with barrier modulation as described in claim 1, characterized in that, The composite Schottky diode device is further provided with a termination structure around the device, which includes one or more of a P-type termination ring, a field plate termination, or a field oxide termination.

Images