A trench barrier schottky device with high surge capability and a method of fabricating the same

Abstract

This invention belongs to the field of semiconductor devices and provides a trench barrier Schottky device with high surge capability and its fabrication method. The device includes a first conductivity type semiconductor substrate, a first conductivity type drift region disposed thereon, multiple trench structures extending into the drift regions, an insulating layer disposed on the trench sidewalls and bottom, a mesa region located between adjacent trenches, a Schottky contact region disposed on the surface of the mesa region, an anode electrode and a cathode electrode electrically connected thereto, and a second conductivity type region disposed within the drift regions. The second conductivity type region is located below the Schottky contact region, electrically isolated from the anode electrode, and has a predetermined spacing from the trench sidewalls. Under forward surge current conditions, this region injects minority carriers into the drift regions, generating a conductivity modulation effect, causing the current to spread within the drift regions. This invention improves the surge withstand capability and reliability of the device while maintaining low forward voltage drop and good reverse characteristics.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor devices, and specifically relates to a trench barrier Schottky device with high surge capability and its fabrication method. Background Technology

[0002] Schottky diodes are widely used in high-frequency rectifier circuits such as switching power supplies, power management, and industrial electronic equipment due to their advantages such as low forward voltage drop, fast switching speed, and almost no reverse recovery charge.

[0003] However, traditional Schottky devices are unipolar devices, and their conduction relies primarily on majority carriers. When the device is subjected to high current surges such as power-on inrush or lightning strikes, the lack of conductivity modulation effect from minority carrier injection causes the forward voltage drop to rise rapidly with increasing current density, resulting in significant power loss and temperature increase in a short period. Furthermore, large currents tend to concentrate at the edges of the Schottky contact area, forming localized current hotspots, further increasing the local temperature and potentially leading to thermal runaway and device failure.

[0004] To improve the reverse leakage current and breakdown voltage performance of Schottky devices, various structural improvement schemes have been proposed in existing technologies. For example, the MPS (Merged PiN Schottky) structure, by setting a PN junction region on the device surface, enables the device to have lower leakage current under high reverse voltage; the JBS (Junction Barrier Schottky) structure, by setting a PN junction region between the Schottky contact areas, improves reverse characteristics and increases breakdown voltage; the TMBS (Trench MOS Barrier Schottky) structure, by forming trenches on the device surface and setting insulating layers on the trench sidewalls, utilizes the MOS structure to modulate the surface electric field distribution of the device, thereby reducing reverse leakage current and improving breakdown voltage. In addition, there are structures such as Super Junction Schottky, which further improve device performance by optimizing the electric field distribution in the drift region.

[0005] However, the aforementioned improvements have limited effect on enhancing the device's surge current withstand capability. Under high-current impact conditions, current concentration and localized overheating can still easily occur inside the device. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a trench barrier Schottky device with high surge capability and its fabrication method. While maintaining the low forward voltage drop and good reverse characteristics of the trench barrier Schottky device, it enables the device to maintain the unipolar Schottky conduction characteristics under normal operating conditions, and realizes a dynamic conduction mechanism from unipolar conduction to bipolar conduction modulation under surge current conditions, thereby improving the surge withstand capability and reliability of the device.

[0007] The main technical solution adopted in this invention is as follows:

[0008] A trench barrier Schottky device with high surge capability, comprising:

[0009] First conductivity type semiconductor substrate;

[0010] A first conductivity type epitaxial layer disposed on the semiconductor substrate serves as a drift region;

[0011] Multiple trench structures extend downward from the upper surface of the epitaxial layer into the interior of the drift region, and a mesa region is formed between adjacent trench structures;

[0012] An insulating layer is provided on the sidewalls and bottom of the trench structure;

[0013] A Schottky contact region is disposed on the surface of the mesa region and is formed by direct contact between the anode electrode and the semiconductor material of the mesa region;

[0014] A cathode electrode is disposed on the back side of the semiconductor substrate; and

[0015] At least one region of a second conductivity type is completely embedded within the drift region and does not extend to the device surface;

[0016] in,

[0017] The second conductivity type region is at least partially located below the Schottky contact region in the vertical projection;

[0018] The second conductive type region has a predetermined distance in the horizontal direction between it and the sidewall of the trench structure.

[0019] Preferably, under forward surge current conditions, when the PN structure formed between the second conductivity type region and the drift region is turned on, the second conductivity type region injects minority carriers into the drift region, thereby generating a conductivity modulation effect in the drift region.

[0020] Preferably, the depth of the trench structure is greater than the maximum junction depth of the second conductivity type region away from the device surface.

[0021] Preferably, the second type of conductive regions are distributed in a discontinuous array below the platform area.

[0022] Preferably, the preset spacing is 0.2µm to 2µm.

[0023] Preferably, the insulating layer continuously covers the sidewalls and bottom of the trench structure, and the opening of the trench structure is flush with the surface of the epitaxial layer.

[0024] Preferably, the second conductivity type regions are arranged periodically along the surface of the device.

[0025] Preferably, the second conductive type region is distributed in an island-like structure, a linear strip array, a rectangular array, or a hexagonal array.

[0026] Preferably, the doping concentration of the second conductivity type region is greater than the doping concentration of the drift region.

[0027] Preferably, the plurality of the trench structures are arranged periodically along the surface of the device to form a device unit structure.

[0028] A method for fabricating a trench barrier Schottky device with high surge capability, the specific steps of which are as follows:

[0029] Step 1: Provide a semiconductor substrate, and epitaxially grow an epitaxial layer on the semiconductor substrate to form a drift region;

[0030] Step 2: Form a second conductivity type region in the drift region;

[0031] Step 3: Form a trench extending downward from the surface of the epitaxial layer into the interior of the drift region, wherein the trench and the second conductivity type region have a predetermined distance in the horizontal direction;

[0032] Step 4: Form an insulating layer on the sidewalls and bottom of the trench;

[0033] Step 5: Fill the trench with insulating material;

[0034] Step 6: Form a Schottky contact area on the surface of the mesa area between adjacent trench structures;

[0035] Step 7: Deposit metal on the surface of the Schottky contact area to form an anode electrode;

[0036] Step 8: Deposit metal on the back side of the semiconductor substrate to form a cathode electrode.

[0037] Beneficial effects: This invention provides a trench barrier Schottky device with high surge capability and its fabrication method, which has the following advantages:

[0038] (1) The present invention sets a second conductivity type region in the drift region to form a PN structure with the drift region, forming a body injection structure. Under surge current conditions, the PN structure is triggered to conduct, injecting minority carriers into the drift region, generating a conductivity modulation effect, which causes the current to expand inside the drift region and reduces the equivalent resistance and local current density of the drift region, thereby significantly improving the surge current withstand capability of the device.

[0039] (2) Under surge current conditions, the injected minority carriers in the device of the present invention diffuse around the drift region, causing the current to expand laterally and longitudinally from the surface into the bulk, thus expanding the current transmission channel. Compared with the situation in traditional Schottky devices where the current is mainly concentrated in the edge region of the Schottky contact area, the present invention can achieve a more uniform current distribution, effectively suppressing the current concentration phenomenon in the edge region of the Schottky contact and reducing the local current density. Due to the more uniform current distribution, the generation of local hot spots is suppressed, the local temperature rise of the device is reduced, and the peak temperature is lowered, thereby significantly improving the thermal stability and thermal runaway resistance of the device under high current impact conditions.

[0040] (3) In the device of the present invention, under normal operating current conditions, the PN structure formed by the second conductivity type region and the drift region remains in the cut-off state. The device mainly achieves unipolar conduction through the Schottky junction. Therefore, it can maintain the inherent low forward voltage drop characteristics and fast switching characteristics of the Schottky device and will not increase the conduction loss under normal operating conditions.

[0041] (4) Based on the standard trench barrier Schottky (TMBS) process, the present invention can realize the body region injection structure by adding only one injection and annealing step. It has good compatibility with existing process platforms, is easy to implement and has controllable cost.

[0042] (5) The present invention improves the electric field distribution on the surface of the device and reduces reverse leakage through the trench structure. The body injection structure participates in conduction under forward surge conditions and generates conductivity modulation effect. The two work together to improve the surge current withstand capability of the device while maintaining good reverse characteristics, and realizes a dynamic conduction mechanism from unipolar conduction to bipolar conductivity modulation. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the overall cross-sectional structure of Example 1;

[0044] Figure 2 This is a partially enlarged schematic diagram of the unit structure in Example 1;

[0045] Figure 3 This is a schematic diagram of the conduction path of the device in Example 1 under normal low current conditions;

[0046] Figure 4This is a schematic diagram of the conduction path of the device in Example 1 under surge current conditions;

[0047] Figure 5 This is a top view of the unit structure layout in Example 1;

[0048] In the figure: semiconductor substrate 10, drift region 20, trench structure 30, insulating layer 40, mesa region 50, Schottky contact region 60, anode electrode 70, cathode electrode 80, and second conductivity type region 90. Detailed Implementation

[0049] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application are clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0050] Example 1

[0051] Taking an example where the first conductivity type is N-type and the second conductivity type is P-type, such as Figures 1 to 5 As shown, this embodiment provides a trench barrier Schottky device, including: a first conductivity type semiconductor substrate 10, a first conductivity type drift region 20, a plurality of trench structures 30, an insulating layer 40, a mesa region 50, a Schottky contact region 60, an anode electrode 70, a cathode electrode 80, and a second conductivity type region 90.

[0052] like Figure 1 As shown, the first conductivity type semiconductor substrate 10 is the base material of this device. In this embodiment, the semiconductor substrate 10 is an N-type heavily doped silicon substrate. In other embodiments, the first conductivity type may also be P-type.

[0053] A first conductivity type drift region 20 is disposed on the semiconductor substrate 10. In this embodiment, the drift region 20 is a first conductivity type epitaxial layer.

[0054] Multiple trench structures 30 extend downward from the device surface into the interior of the drift region 20.

[0055] like Figure 1 As shown, in this embodiment, the insulating layer 40 continuously covers the sidewalls and bottom of the trench structure 30, and the opening of the trench structure 30 is flush with the device surface. In this embodiment, the insulating layer 40 is a silicon oxide layer, and the trench structure 30 is preferably filled with an insulating material. Figure 5 As shown, multiple trench structures are arranged periodically along the surface of the device to form a device unit structure.

[0056] Mesa regions 50 are formed between adjacent trench structures. The anode electrode 70 forms a Schottky contact 60 only with the semiconductor material on the surface of the mesa region 50, and does not form a conductive contact with the insulating material in the trench structure 30. A cathode electrode 80 is disposed on the back side of the semiconductor substrate 10. In this embodiment, the Schottky contact region 60 forms a Schottky barrier interface through direct contact between the anode electrode 70 and the mesa region 50. The width of the mesa region 50 located between adjacent trench structures is determined by the spacing between the adjacent trench structures.

[0057] At least one second conductivity type region 90 is disposed within the drift region 20, and the second conductivity type region 90 forms a PN junction with the drift region 20. In this embodiment, the second conductivity type region 90 is a P-type doped region. In other embodiments, when the first conductivity type is P-type, the second conductivity type can be N-type.

[0058] In this embodiment, the second conductivity type region 90 is at least partially located below the Schottky contact region 60 in vertical projection and is electrically isolated from the anode electrode 70. Specifically, the second conductivity type region 90 is completely located inside the drift region 20 and does not directly contact the anode electrode 70 on the device surface, forming a buried bulk injection structure, which differs from the way the PN structure is set on the device surface in traditional JBS or MPS structures.

[0059] The second conductive type region 90 has a predetermined spacing in the horizontal direction between it and the sidewall of the trench structure. In one specific embodiment, the predetermined spacing is 0.2µm to 2µm.

[0060] In a preferred embodiment, the depth of the trench structure is greater than the junction depth of the second conductivity type region 90 away from the device surface, so that the trench electric field modulation structure and the second conductivity type region 90 form a specific spatial relationship in the longitudinal direction, thereby improving the electric field distribution on the device surface and providing structural conditions for the formation of a minority carrier diffusion region inside the drift region.

[0061] In a preferred embodiment, the second conductivity type regions 90 are distributed in a discontinuous array below the mesa region 50 and are periodically arranged along the device surface. Specifically, the second conductivity type regions 90 may have an island structure, a strip structure, or a rectangular array (e.g., Figure 5 As shown), the distribution is a hexagonal array or a linear strip array, and its period is used to adjust the current distribution and the uniformity of minority carrier injection.

[0062] In a preferred embodiment, the doping concentration of the second conductivity type region 90 is greater than the doping concentration of the drift region 20. Specifically, the doping concentration of the second conductivity type region 90 is preferably one to three orders of magnitude greater than the doping concentration of the drift region 20, in order to improve the minority carrier injection efficiency when the PN junction is turned on, thereby enhancing the conductivity modulation effect.

[0063] Unlike traditional trench barrier Schottky structures that utilize P+ shielding to improve reverse withstand voltage, the second conductivity type region 90 is primarily used to form minority carrier injection paths under high current conditions, rather than for reverse electric field shielding or reverse blocking. By setting the second conductivity type region 90 below the Schottky contact region 60, the device can form a current transport structure involving both the Schottky conduction path and the PN structure conduction path under high current conditions. This facilitates the lateral and longitudinal expansion of current in the drift region 20, reduces local current density, and improves the device's surge current withstand capability.

[0064] This embodiment provides a method for fabricating a trench barrier Schottky device, used to fabricate the device of Example 1, specifically including the following steps:

[0065] Step 1: Provide a semiconductor substrate 10 of a first conductivity type, and epitaxially grow an epitaxial layer of the first conductivity type on the semiconductor substrate 10 to form a drift region 20 of the first conductivity type. In a specific embodiment, the thickness of the epitaxial layer is 10-50µm.

[0066] Step 2: A second conductivity type region 90 is formed in the drift region, and the second conductivity type region 90 forms a PN junction with the drift region 20. In one specific embodiment, multiple second conductivity type regions 90 are formed in a discontinuous array in the drift region 20 by ion implantation followed by annealing.

[0067] Step 3: Form a trench extending downward from the device surface into the drift region 20. The trench structure and the second conductivity type region 90 have a predetermined spacing in the horizontal direction. In one specific embodiment, the trench is formed on the device surface by photolithography and etching processes, extending into the drift region 20. The trench depth is 3-10µm, the trench width is 0.5-2µm, and the trench spacing is 2-6µm.

[0068] Step 4: Form an insulating layer 40 on the inner wall of the trench. In one embodiment, the insulating layer can be formed by a thermal oxidation process. In other embodiments, it can also be formed by chemical vapor deposition (CVD), atomic layer deposition (ALD), or physical vapor deposition (PVD).

[0069] Step 5: Deposit insulating material in the trench and perform planarization treatment to form the trench structure.

[0070] Step 6: Form a Schottky contact region 60 on the surface of the mesa region 50 between adjacent trench structures. In one specific embodiment, the Schottky contact region 60 is formed using a selective region metal deposition process.

[0071] Step 7: Deposit metal on the surface of the Schottky contact region 60 to form the anode electrode 70.

[0072] Step 8: Deposit metal on the back side of the semiconductor substrate 10 to form a cathode electrode 80.

[0073] The working principle of this invention is as follows:

[0074] The trench barrier Schottky device provided by the present invention forms a buried body injection structure by setting a second conductivity type region 90 inside the drift region 20, so that the device exhibits different conduction mechanisms under different current conditions, thereby effectively improving the surge current withstand capability while maintaining the low forward voltage drop characteristics of the Schottky device.

[0075] Under different current conditions, the device of the present invention mainly operates under the following two conduction mechanisms: unipolar conduction mechanism and bipolar conductance modulation conduction mechanism.

[0076] (1) Normal working mode: Unipolar conduction mechanism

[0077] like Figure 3 As shown in the figure, the arrows indicate the flow paths of majority carrier electrons. Within the normal operating current range, after a forward bias is applied to the anode electrode 70, the Schottky junction formed by the Schottky contact region 60 and the drift region 20 is the first to conduct. Current flows from the anode electrode 70 through the Schottky contact region 60 into the drift region 20, and then is transported longitudinally in the drift region 20 to the semiconductor substrate 10 in the form of majority carriers.

[0078] Under these operating conditions, due to the low current density inside the device, the voltage drop across the drift region 20 is small, and the PN junction formed between the second conductivity type region 90 and the drift region 20 is in the off state. Therefore, the device conduction is mainly driven by majority carriers, exhibiting typical unipolar conduction characteristics, thus maintaining the inherent low forward voltage drop and fast switching characteristics of Schottky devices.

[0079] (2) Surge current mode: bipolar conductivity modulation conduction mechanism

[0080] like Figure 4 As shown in the figure, the arrows indicate the path of minority carriers (holes) injected from the second conductivity type region 90 into the drift region 20, demonstrating the lateral and longitudinal diffusion distribution of current within the drift region under the conductivity modulation effect.

[0081] When the device is subjected to a transient surge current, the current density flowing through the Schottky contact region 60 and the drift region 20 below it increases significantly. As the current density increases, the resistive voltage drop in the drift region 20 gradually increases, especially in the region below the mesa region 50. This resistive voltage drop, combined with the forward voltage drop of the Schottky junction, causes the potential of the second conductivity type region 90 relative to the drift region 20 to increase, thereby promoting the conduction of the PN structure.

[0082] When the PN structure is turned on, the second conductivity type region 90 injects minority carriers (holes) into the drift region 20, creating a region with increased minority carrier concentration within the drift region 20. To maintain electrical neutrality, the majority carrier concentration in the drift region 20 also increases, resulting in a conductivity modulation effect. Under this effect, the equivalent resistance of the drift region 20 is significantly reduced, and the on-resistance of the device under high current conditions is decreased. Simultaneously, the injected minority carriers diffuse laterally and longitudinally within the drift region, extending the current transport path from the surface region to the bulk region, thereby mitigating the current concentration phenomenon at the Schottky contact edge and reducing the local current density.

[0083] Through the aforementioned bipolar conductivity modulation and current diffusion effect, the device can effectively suppress the formation of local hot spots under transient surge conditions and improve surge current withstand capability.

[0084] (3) Unipolar-bipolar dynamic conduction mechanism

[0085] In summary, this invention enables the device to dynamically switch its conduction mechanism based on the current level by forming a body injection structure within a second conductivity type region 90 inside the drift region 20.

[0086] Under normal operating conditions, the device maintains unipolar conduction characteristics, keeping low forward voltage drop and fast switching characteristics. Under larger current conditions, the PN structure conducts and triggers minority carrier injection, generating a bipolar conductance modulation effect, thereby reducing the drift region resistance, improving the surge current withstand capability and thermal reliability of the device, and enabling the device to adaptively switch the conduction mechanism according to the current level.

[0087] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A trench barrier Schottky device with high surge capability, characterized in that, include: First conductivity type semiconductor substrate (10); A first conductivity type epitaxial layer is disposed on the semiconductor substrate (10) as a drift region (20). Multiple trench structures (30) extend downward from the upper surface of the epitaxial layer into the interior of the drift region (20), and a mesa region (50) is formed between adjacent trench structures. An insulating layer (40) is provided on the sidewalls and bottom of the trench structure (30); A Schottky contact region (60) is disposed on the surface of the mesa region (50) and is formed by direct contact between the anode electrode (70) and the semiconductor material of the mesa region (50); A cathode electrode (80) is disposed on the back side of the semiconductor substrate (10); as well as At least one second conductivity type region (90) is completely embedded inside the drift region (20) and does not extend to the device surface; in, The second conductivity type region (90) is at least partially located below the Schottky contact region (60) in the vertical projection; The second conductive type region (90) and the sidewall of the trench structure (30) have a predetermined spacing in the horizontal direction.

2. The trench barrier Schottky device with high surge capability according to claim 1, characterized in that: Under forward surge current conditions, when the PN structure formed between the second conductivity type region (90) and the drift region (20) is turned on, the second conductivity type region (90) injects minority carriers into the drift region (20), thereby generating a conductivity modulation effect in the drift region (20).

3. The trench barrier Schottky device with high surge capability according to claim 1, characterized in that, The depth of the trench structure (30) is greater than the maximum junction depth of the second conductivity type region (90) away from the device surface.

4. The trench barrier Schottky device with high surge capability according to claim 1, characterized in that, The second type of conductive region (90) is distributed in a discontinuous array below the platform region (50).

5. The trench barrier Schottky device with high surge capability according to claim 1, characterized in that, The preset spacing is 0.2µm to 2µm.

6. The trench barrier Schottky device with high surge capability according to claim 1, characterized in that, The insulating layer (40) continuously covers the sidewalls and bottom of the trench structure (30), and the opening of the trench structure (30) is flush with the surface of the epitaxial layer.

7. The trench barrier Schottky device with high surge capability according to claim 1, characterized in that, The second type of conductive region (90) is arranged periodically along the surface of the device.

8. The high surge capability trench barrier Schottky device according to claim 7, characterized in that, The second type of conductive region (90) is distributed in the form of island structure, linear strip array, rectangular array, and hexagonal array.

9. The trench barrier Schottky device with high surge capability according to claim 1, characterized in that: The doping concentration of the second conductivity type region (90) is greater than the doping concentration of the drift region (20).

10. The trench barrier Schottky device with high surge capability according to claim 1, characterized in that: Multiple trench structures are arranged periodically along the surface of the device to form a device unit structure.

11. A method for fabricating a trench barrier Schottky device with high surge capability, characterized in that, The specific steps for fabricating the trench barrier Schottky device according to any one of claims 1-10 are as follows: Step 1: Provide a semiconductor substrate (10), and grow an epitaxial layer on the semiconductor substrate (10) to form a drift region (20). Step 2: Form a second conductivity type region (90) in the drift region; Step 3: Form a trench extending downward from the surface of the epitaxial layer into the interior of the drift region (20), wherein the trench and the second conductivity type region (90) have a predetermined distance in the horizontal direction; Step 4: Form an insulating layer (40) on the sidewalls and bottom of the trench; Step 5: Fill the trench with insulating material; Step 6: Form a Schottky contact area (60) on the surface of the mesa area (50) between adjacent trench structures; Step 7: Deposit metal on the surface of the Schottky contact area (60) to form an anode electrode (70); Step 8: Deposit metal on the back side of the semiconductor substrate (10) to form a cathode electrode (80).

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