A low emi trench schottky diode
By introducing a dielectric layer isolation structure between the polysilicon region and the anode in the trench Schottky diode, and connecting the MOS junction capacitance and the polysilicon resistor in series, the EMI noise problem during the turn-off of the trench Schottky diode is solved, resulting in lower switching losses and noise.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUANG WEI INTEGRATION TECH (SHENZHEN) CO LTD
- Filing Date
- 2022-11-01
- Publication Date
- 2026-06-05
AI Technical Summary
Trench Schottky diodes are prone to significant switching losses and high-frequency EMI noise when turned off, mainly due to the interaction between parasitic capacitance and inductance.
In trench Schottky diodes, a dielectric layer isolation structure is introduced between the polysilicon region and the anode, so that the MOS junction capacitance and the polysilicon resistor are connected in series to form an equivalent series circuit to slow down the voltage change rate, reduce reverse current and restore charge.
It effectively reduces EMI noise during trench Schottky diode turn-off, reduces reverse recovery current by 15%, reverse recovery time by 10%, Qrr by 30%, and reduces fast turn-off losses of the device.
Smart Images
Figure CN115881828B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor technology, and more particularly to a low-EMI trench Schottky diode. Background Technology
[0002] The Schottky diode is named after its inventor, Dr. Schottky, and is short for Schottky Barrier Diode (SBD). Unlike other diodes, which are made using the PN junction principle (forming a PN junction between P-type and N-type semiconductors), Schottky diodes utilize the metal-semiconductor junction principle (forming a metal-semiconductor junction). Therefore, they are also called metal-semiconductor (contact) diodes or surface barrier diodes. They are majority-carrier devices with fast switching speeds and low turn-on voltages, widely used as power rectifiers in switching power supplies and other high-speed power switching equipment.
[0003] TMBS (Trench Schottky Diode) adds a polysilicon-filled anode trench structure to the traditional planar Schottky diode. The lateral electric field generated by the trench during reverse blocking can effectively suppress the surface barrier reduction effect of Schottky, reducing the leakage current of the device. At the same time, due to the electric field adjustment effect of the trench, the device breakdown voltage is increased, and the on-state voltage drop is reduced at the same breakdown voltage, further broadening the application range of Schottky diodes.
[0004] Trench Schottky diodes are primarily used in fast-charging power supplies. In AC-DC converters, they act as rectifier diodes in the secondary circuit. When the secondary circuit is on, the trench Schottky diode is forward-biased. Due to the barrier capacitance of the Schottky junction, when the secondary circuit is off, the Schottky diode needs to switch from the forward-biased state to the blocking state, requiring charging of the Schottky diode capacitor. This charging process generates a reverse overshoot current, drawing electrons from the drift region and generating a reverse recovery charge Qrr. Simultaneously, the charging parasitic capacitance charges the parasitic inductance in the circuit, thus generating high-frequency oscillating EMI.
[0005] Traditional Schottky diodes only have the Schottky junction barrier capacitor C. Schottky This capacitance value is related to the chip area and the barrier height; for trench Schottky diodes, due to the deep trench structure, their parasitic capacitance is not only the Schottky barrier capacitance C. Schottky There is also the MOS junction capacitance C formed by the trench structure. MOS Because the trench is deep and accounts for a large proportion, it is much larger than the junction barrier capacitance C. Schottky This is detrimental to device turn-off, therefore trench Schottky diodes tend to generate greater switching losses and higher EMI noise compared to planar Schottky diodes. Summary of the Invention
[0006] This application provides a low-EMI trench Schottky diode to reduce EMI noise when the trench Schottky diode is turned off without affecting other characteristics of the trench Schottky diode.
[0007] This application provides a low-EMI trench Schottky diode, comprising:
[0008] Anode 101, metal, is in Schottky contact with epitaxial layer 202. Polysilicon region 203 is disposed in epitaxial layer 202. A portion of polysilicon 203 is in contact with anode 101. A dielectric layer 302 isolates anode 101 from polysilicon 203 in an active region. The active region is larger than the portion of the active region.
[0009] An epitaxial layer 202 is disposed between the anode 101 and the substrate layer 201, and a polysilicon region 203 is disposed therein. The polysilicon 203, except for the region in contact with the anode 101, is encapsulated based on the dielectric layer 302 and the gate oxide layer 301.
[0010] The substrate layer 201 is disposed between the cathode 102 and the epitaxial layer 202;
[0011] Cathode 102, metal.
[0012] Optionally, the polycrystalline silicon region 203 is lightly doped or naturally doped, wherein the light doping is used to dop in impurities;
[0013] The ion implantation dose of the polycrystalline silicon region 203 satisfies 1e11-1e12cm. -2 ;
[0014] The resistivity of the polycrystalline silicon region 203 satisfies 10. 3 Ω.cm-10 6 Ω.cm.
[0015] Optionally, the anode 101 contacts a portion of the polycrystalline silicon 203 at its end edge 204 region.
[0016] Optionally, the polycrystalline silicon region 203 has a SIPOS structure.
[0017] Optionally, the substrate layer 201 is a heavily doped N-type substrate layer, and the epitaxial layer 202 is a lightly doped N-type epitaxial layer.
[0018] Optionally, the dielectric layer 302 is silicon dioxide or silicon nitride, and its thickness is 0.5μm-2μm.
[0019] Optionally, the anode 101 may be made of titanium, nickel, vanadium, or platinum.
[0020] In this embodiment of the application, the anode of the Schottky diode is in contact with the polysilicon region at the end edge region, and the anode is isolated from the polysilicon region by a dielectric layer. The circuit design is equivalent to the MOS junction capacitance and the polysilicon resistor being connected in series and then in contact with the anode metal, thereby reducing the EMI noise of the trench Schottky diode when it is turned off without affecting other characteristics of the trench Schottky diode.
[0021] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description
[0022] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:
[0023] Figure 1 This is an example of a trench Schottky diode structure in the prior art;
[0024] Figure 2 This is an example of a parasitic capacitance model for existing trench Schottky diodes;
[0025] Figure 3 This is an example of a trench Schottky diode structure according to an embodiment of this application;
[0026] Figure 4 This is a parasitic capacitance model of a trench Schottky diode according to an embodiment of this application.
[0027] Figure 5 This is a comparison of the turn-off characteristics of the Schottky diodes in the embodiments of this application. Detailed Implementation
[0028] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
[0029] Traditional trench Schottky diodes, such as Figure 1As shown, the diagram depicts a half-cell structure. The upper metal electrode 101 forms a Schottky barrier contact with the N-drift region 202. This part is the active region, i.e., the region where the forward conduction current flows, and also constitutes the Schottky junction capacitance C. Schottky The upper metal electrode 101, heavily doped N+ polysilicon 203, gate oxide layer 301, and N- drift region 202 form a MOS capacitor structure. The metal electrode 101 and heavily doped N+ polysilicon 203 have an ohmic contact. The thickness of the gate oxide layer 301 is between 0.08 μm and 0.8 μm, determined by the TMBS voltage and device leakage current. This part of the structure acts as a shield, reducing reverse leakage current and increasing reverse breakdown voltage. Its equivalent circuit is shown below. Figure 2 As shown. Due to the MOS junction capacitance C MOS The trench depth is mainly related to the thickness of the gate oxide layer 301 and the area enclosed by the gate oxide layer 301 and the N-drift region 202. To limit the Schottky surface barrier reduction effect, the trench depth is generally quite deep. The MOS junction capacitance C... MOS The proportion is very large, and it is easy to generate large reverse leakage current and large turn-off charge when the device is turned off. It is easy to generate oscillation with the circuit parasitic inductance and generate EMI noise.
[0030] This application provides a low-EMI trench Schottky diode, comprising:
[0031] Anode 101, made of metal, has a Schottky contact with epitaxial layer 202. Polysilicon region 203 is disposed within epitaxial layer 202. A portion of polysilicon 203 contacts anode 101, and a dielectric layer 302 isolates the active region of anode 101 from the polysilicon 203. The active region is larger than the partially isolated region. Specifically, as shown... Figure 3 As shown, the lower surface of the anode 101 is in contact with the upper surface of the epitaxial layer 202. A polysilicon region 203 is disposed within the epitaxial layer 202. The upper surface of the epitaxial layer 202 and part of the upper surface of the polysilicon region 203 are in contact with the lower surface of the anode 101. A dielectric layer 302 is disposed between the lower surface of the anode 101 and the remaining polysilicon region 203 to achieve isolation. The upper surface area of the dielectric layer 302 is larger than the contact area between the polysilicon region 203 and the lower surface of the anode 101.
[0032] Specifically, the contact position and size of the contact portion between the polysilicon region 203 and the lower surface of the anode 101 are not specifically limited here. By designing the upper surface area of the dielectric layer 302 to be larger than the contact area between the polysilicon region 203 and the lower surface of the anode 101, that is, the first contact area between the dielectric layer 302 and the lower surface of the anode 101 is larger than the second contact area between the polysilicon region 203 and the lower surface of the anode 101, the equivalent series polysilicon resistance Rpoly can be maximized. In some embodiments, the blocking area of the dielectric layer 302 is much larger than the contact hole area, thus the larger the blocking area, the larger Rpoly. The contact hole formed in the embodiments of this application can be made simultaneously with the Schottky contact of the active region without the need for an additional photomask.
[0033] An epitaxial layer 202 is disposed between the anode 101 and the substrate layer 201, and a polysilicon region 203 is disposed therein. The polysilicon 203, except for the region in contact with the anode 101, is encapsulated by the dielectric layer 302 and the gate oxide layer 301. That is, the polysilicon 203 is only connected to the anode 101 through contact holes, and the remaining part is covered by the gate oxide layer 301 and the dielectric layer 302.
[0034] The substrate layer 201 is disposed between the cathode 102 and the epitaxial layer 202;
[0035] Cathode 102, metal.
[0036] In this embodiment of the application, the anode of the Schottky diode is in contact with the polysilicon region at the end edge region, and the anode is isolated from the polysilicon region by a dielectric layer. The circuit design is equivalent to the MOS junction capacitance and the polysilicon resistor being connected in series and then in contact with the anode metal, thereby reducing the EMI noise of the trench Schottky diode when it is turned off without affecting other characteristics of the trench Schottky diode.
[0037] In some embodiments, the anode 101 contacts a portion of the polysilicon 203 at the end edge 204 region. The position of the contact hole can also be adjusted according to the actual process and needs, and the specific position is not limited here.
[0038] In some embodiments, the polysilicon region 203 is lightly doped, or naturally doped, wherein the light doping is used to dope impurities. The ion implantation dose of the polysilicon region 203 satisfies 1e11cm. -2 -1e12cm -2 The resistivity of the polycrystalline silicon region 203 satisfies 10. 3 Ω.cm-10 6 Ω.cm. In practical applications, doping can be achieved using ion implantation, and doping can involve impurities such as boron, aluminum, arsenic, and phosphorus, with an ion implantation dose of 1e11cm. -2-1e12cm -2 Its resistivity is 10 3 Ω.cm-10 6 Between Ω·cm. Alternatively, ion implantation can be avoided, and high-resistivity polycrystalline silicon resistors can be formed through natural doping.
[0039] In some embodiments, the polycrystalline silicon region 203 is a SIPOS structure. The SIPOS structure, having a silicon dioxide composition, can achieve a resistivity of 1e7Ω·cm to 1e12Ω·cm.
[0040] In some embodiments, the substrate layer 201 is a heavily doped N-type substrate layer, and the epitaxial layer 202 is a lightly doped N-type epitaxial layer.
[0041] In some embodiments, the dielectric layer 302 is silicon dioxide or silicon nitride, and its thickness is 0.5μm-2μm. By designing the dielectric layer 302, this application can effectively reduce the coupling capacitance between the polysilicon layer 203 and the anode 101 metal.
[0042] In some embodiments, the anode 101 is made of titanium, nickel, vanadium, or platinum. Different metals have different work functions, resulting in different barrier heights for the formed Schottky barrier diodes.
[0043] The low-EMI trench Schottky diode structure proposed in this application adopts an N-high-resistivity polysilicon 203 structure, and a gate oxide layer 302 structure is designed between the N-high-resistivity polysilicon 203 structure and the anode 101 metal. An opening 204 is only made in the chip portion (e.g., the end terminal region) to connect with the anode 101 metal. Circuitally, this is equivalent to the MOS junction capacitance being connected in series with the N-polysilicon 203 resistor before contacting the anode 101 metal. Figure 4 As shown, this large series resistance is determined by the polysilicon 203 structure resistance and is related to the chip size. The larger the chip and the longer the strip cell, the larger the series resistance value. When the device is reverse-biased off, the device voltage change dv / dt is affected by the voltage division effect of the MOS resistor Rpoly, and the MOS junction capacitance C... MOS The voltage change rate is significantly reduced, resulting in lower reverse current, reduced reverse recovery charge Qrr, and consequently lower EMI noise. This is achieved by simulating diode turn-off characteristics through circuit device hybridization, such as... Figure 5 As shown, the reverse recovery current of the Schottky diode structure of this application is reduced by 15% compared with the traditional structure, the reverse recovery time is reduced by 10%, and Qrr is reduced by 30%, which reduces the fast turn-off loss of the device and can effectively reduce the EMI noise of the device.
[0044] It should be noted that, in the embodiments of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.
[0045] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.
[0046] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims. All of these forms are within the protection scope of this application.
Claims
1. A low-EMI trench Schottky diode, characterized in that, include: The anode (101) is metal and has a Schottky contact with the epitaxial layer (202). A polysilicon region (203) is disposed in the epitaxial layer (202). A portion of the polysilicon region (203) is in contact with the anode (101). The anode (101) is isolated from the polysilicon region (203) by a dielectric layer (302). The first contact area between the dielectric layer (302) and the lower surface of the anode (101) is greater than the second contact area between the polysilicon region (203) and the lower surface of the anode (101). An epitaxial layer (202) is disposed between the anode (101) and the substrate layer (201), and the polysilicon region (203) except for the region in contact with the anode (101) is encapsulated based on the dielectric layer (302) and the gate oxide layer (301); A substrate layer (201) is disposed between the cathode (102) and the epitaxial layer (202); The cathode (102) is metallic.
2. The low-EMI trench Schottky diode as described in claim 1, characterized in that, The polycrystalline silicon region (203) is lightly doped or naturally doped, wherein the light doping is performed by ion implantation process to dop the impurities; The ion implantation dose of the polycrystalline silicon region (203) satisfies 1e11-1e12cm. -2 ; The resistivity of the polycrystalline silicon region (203) satisfies 10. 3 Ω.cm-10 6 Ω.cm.
3. The low-EMI trench Schottky diode as described in claim 1, characterized in that, The anode (101) contacts a portion of the polysilicon region (203) at its end edge (204) region.
4. The low-EMI trench Schottky diode as described in claim 1, characterized in that, The polycrystalline silicon region (203) has a SIPOS structure.
5. The low-EMI trench Schottky diode as described in claim 1, characterized in that, The substrate layer (201) is a heavily doped N-type substrate layer, and the epitaxial layer (202) is a lightly doped N-type epitaxial layer.
6. The low-EMI trench Schottky diode as described in claim 1, characterized in that, The dielectric layer (302) is silicon dioxide or silicon nitride, and its thickness is 0.5μm-2μm.
7. The low-EMI trench Schottky diode as described in claim 1, characterized in that, The anode (101) is made of titanium, nickel, vanadium or platinum.