HEMT device with back field plate structure and preparation method thereof
By etching right-angle trapezoidal grooves on the Si substrate and depositing metal films to form a backfield plate structure, the problem of breakdown of GaN HEMT on the Si substrate under high voltage is solved, and higher breakdown voltage and heat dissipation performance are achieved, which extends the length of the The device life span.
Patent Information
- Application Number
- CN201810174890.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2018-03-02
- Publication Date
- 2024-12-31
- Estimated Expiration
- 2038-03-02
AI Technical Summary
Si substrate GaN HEMT is prone to breakdown at high pressure, limiting its working power, and existing improvements cannot fundamentally change the narrow bandgap properties of Si materials. Increasing the thickness of the outer protrusion buffer layer will increase production costs and heat dissipation challenges.
The backfield plate structure is adopted, and by etching right-angle trapezoidal grooves on the silicon substrate and depositing a metal film, the backfield plate structure is formed, the isolation substrate is turned on and the electric field peak on the gate drain side is reduced, while the heat dissipation performance is improved.
It effectively improves breakdown voltage and heat dissipation performance, so that the Si substrate HEMT can work normally at 1kV voltage, extending device life and reducing working temperature.
Smart Images
Figure CN108231882B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a high electron mobility transistor (HEMT), and in particular to a HEMT device with a back field plate structure and a preparation method thereof. Background Art
[0002] Power electronic devices are widely used in many fields such as household appliances, industrial equipment, and automotive power supplies. The new generation of power electronic devices requires higher efficiency, higher power density, and higher reliability in high-temperature working environments. At present, silicon-based power devices, such as MOSFET and IGBT, are commonly used in power electronic devices. However, after a long period of development, the performance of silicon electronic power devices has reached the theoretical limit of its materials. The new generation of power electronic devices faces huge challenges such as high voltage, high frequency, and small size. The third-generation semiconductor material GaN has the advantages of large bandgap width, high saturated electron migration speed, and stable chemical properties. Therefore, power electronic devices based on GaN materials have the advantages of small on-resistance, fast switching speed, high voltage resistance, and good high temperature resistance. On the other hand, GaN can be grown on Si, SiC, and sapphire. The GaN high electron mobility transistor is a power electronic device based on GaN material. It forms an AlGaN / GaN heterojunction through epitaxy. After the modulation of the polarization electric field, a surface density of 10 can be formed at the heterojunction interface even without artificial doping. 13 cm-2 two-dimensional electron gas. Since the material is not doped, the mobility of electrons in GaN in the two-dimensional plane exceeds 2000cm 2 / Vs. This makes GaN HEMT have the characteristics of low on-resistance and high operating frequency. It can meet the requirements of the new generation of power electronic devices for higher power, higher frequency, smaller size and high temperature working conditions, and can be applied to AC / DC, DC / DC converters, DC / AC motor drives and photovoltaic power generation.
[0003] Since Si substrates have the advantages of low price, mature process, and large diameter, the preparation of GaN HEMTs on Si substrates has become a research hotspot. Among them, a major hotspot in the research of HEMT devices is the breakdown problem under high-voltage working conditions. Due to the presence of the largest electric field at the edge of the gate drain side, electrical breakdown and thermal breakdown are easily caused under high voltage and fast switching conditions. In addition, Si material has a low bandgap width, and the Si substrate becomes the weakest part of the device, which is easily broken down by high voltage, limiting the application of GaN HEMTs on Si substrates under high voltage. Usually, GaN HEMTs on Si substrates are used below 1000V, which limits their operating power.
[0004] Existing measures to improve device breakdown voltage include setting a field plate structure to reduce the gate electric field density; compensatory doping to obtain a high-resistance Si substrate, which cannot fundamentally change the narrow bandgap nature of the Si material; and increasing the thickness of the epitaxial buffer layer to increase the off-state resistance. This method takes a long time for epitaxial growth, greatly increases production costs, and increases epitaxial thickness, which also poses a higher challenge to the device's heat dissipation performance. Summary of the invention
[0005] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the object of the present invention is to provide a HEMT device with a back field plate structure, which not only solves the problem that the existing Si substrate HEMT is prone to breakdown at the silicon substrate during high-voltage operation, but also solves the problem that electrical breakdown and thermal breakdown occur on the gate drain side, thereby achieving normal operation of the Si substrate HEMT at a voltage of 1 kV.
[0006] Another object of the present invention is to provide a method for preparing the HEMT device with a back field plate structure.
[0007] The purpose of the present invention is achieved through the following technical solutions:
[0008] A HEMT device with a back field plate structure comprises, from bottom to top, a silicon substrate, a GaN epitaxial layer, an AlGaN barrier layer, and a Si3N4 passivation protection layer; a gate electrode, a source electrode, and a drain electrode are arranged on the AlGaN barrier layer; the silicon substrate is provided with a groove with a right-angle trapezoidal cross section; the groove opens downward, and the top of the groove is the lower surface of the GaN epitaxial layer; the back field plate structure is arranged on a portion of the lower surface of the silicon substrate, the inclined surface of the groove, and a portion of the top of the groove.
[0009] The contact line width between the back field plate structure and the GaN epitaxial layer is 5-10 μm.
[0010] The lateral width of the portion of the top of the groove not covered by the back field plate structure is 5-10 μm.
[0011] The back field plate structure is a metal film obtained by electron beam evaporation deposition, and has a thickness of 50nm to 2μm.
[0012] A method for preparing a HEMT device with a back field plate structure comprises the following steps:
[0013] (1) Using double-sided alignment photolithography technology in the HEMT device, an etching window area is prepared below the gate on the back side of the Si substrate, and the line width in the source and drain direction of the window area is 5 to 10 μm;
[0014] (2) Using a deep silicon etching method, the window area is etched to the GaN epitaxial layer. During the etching process, two re-lithography processes are performed, each time the window is enlarged by 10 to 50 μm toward the source electrode, and finally a groove with a right-angle trapezoidal cross section is obtained;
[0015] (3) using double-sided alignment photolithography technology to prepare a back field plate metal deposition window on the bottom surface of the silicon substrate etched with a groove;
[0016] (4) Ti / Au metal is deposited on part of the lower surface of the silicon substrate, the inclined surface of the groove, and part of the top surface of the groove to form a back field plate structure.
[0017] The thickness of the Si substrate is 300-1000 um.
[0018] The deposition in step (4) is carried out by electron beam evaporation.
[0019] The principle of the present invention is as follows:
[0020] The HEMT device with a back field plate structure of the present invention first isolates the substrate by etching, so that the source and drain cannot be connected through the Si substrate due to the presence of air as a dielectric, and the device is difficult to break down at the narrow bandgap Si substrate, so it can withstand extremely high voltage. Secondly, the bottom evaporated metal is used as a back field plate, which is connected to the source and the packaging material, which can not only weaken the edge electric field peak of the gate drain side and increase the breakdown voltage, but also can act as a heat transfer medium to conduct the heat generated by the device in time, reduce the operating temperature of the device, and increase the service life.
[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:
[0022] (1) The present invention completely isolates the substrate of the HEMT device from the bottom of the gate into two parts, and the air is used as the dielectric between the source and the drain, which can effectively avoid substrate breakdown and improve the breakdown voltage.
[0023] (2) The present invention adopts the method of bottom metal deposition to form the back field plate structure, which can effectively alleviate the electric field peak on the gate drain side, and at the same time can increase heat dissipation and effectively reduce the operating temperature of the device. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 It is a schematic structural diagram of a HEMT device with a back field plate structure according to the present invention. DETAILED DESCRIPTION
[0025] The present invention will be further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.
[0026] Example
[0027] like Figure 1As shown, the HEMT device with a back field plate structure of the present invention includes, from bottom to top, a silicon substrate 2, a GaN epitaxial layer 3, an AlGaN barrier layer 4, and a Si3N4 passivation protection layer 5; a gate electrode 6, a source electrode 7, and a drain electrode 8 are arranged on the AlGaN barrier layer 4; the silicon substrate is provided with a groove 9 with a right-angle trapezoidal cross section; the groove opens downward, and the top of the groove is the lower surface of the GaN epitaxial layer; the back field plate structure 1 is arranged on part of the lower surface of the silicon substrate, the inclined surface of the groove, and part of the top of the groove. The contact line width 10 of the back field plate structure and the GaN epitaxial layer is 5 to 10 μm. The lateral width of the portion 11 of the top of the groove not covered by the back field plate structure is 5 to 10 μm. The back field plate structure is a metal sheet with a thickness of 50nm to 2 μm.
[0028] A method for preparing a HEMT device with a back field plate structure comprises the following steps:
[0029] (1) Using double-sided alignment photolithography technology in the HEMT device, an etching window area is prepared below the back gate of the Si substrate (thickness is 300-1000 μm), and the line width of the window area in the source-drain direction is 5-10 μm;
[0030] (2) Using a deep silicon etching method, the window area is etched to the GaN epitaxial layer. During the etching process, two re-lithography processes are performed, each time the window is enlarged by 10 to 50 μm toward the source electrode, and finally a groove with a right-angle trapezoidal cross section is obtained;
[0031] (3) using double-sided alignment photolithography technology to prepare a back field plate metal deposition window on the bottom surface of the silicon substrate etched with a groove;
[0032] (4) Using electron beam evaporation, Ti / Au metal is deposited on part of the lower surface of the silicon substrate, the inclined surface of the groove, and part of the top surface of the groove to form a back field plate structure.
[0033] The Si substrate GaN HEMT prepared in this embodiment has the back field plate grounded after device packaging. The breakdown voltage tested by a power tester can reach more than 2000V. Device aging analysis shows that the average life of the HEMT device with the back field plate is increased by 20%.
[0034] The present invention adopts an isolation substrate and a back field plate structure to avoid high voltage breakdown of the narrow bandgap Si substrate, effectively alleviate the field intensity peak on the gate drain side, and the bottom metal strengthens the heat dissipation, significantly reducing the device temperature. This structure improves the breakdown voltage and heat dissipation performance of the HEMT device.
[0035] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.
Claims
1. A HEMT device having a back field plate structure, characterized in that: The invention comprises, from bottom to top, a silicon substrate, a GaN epitaxial layer, an AlGaN barrier layer, and a Si3N4 passivation protection layer; a gate electrode, a source electrode, and a drain electrode are arranged on the AlGaN barrier layer; the silicon substrate is provided with a groove with a right-angle trapezoidal cross section, and the right angle of the right-angle trapezoid is located on the side close to the drain electrode; the groove opens downward, and the top of the groove is the lower surface of the GaN epitaxial layer; a back field plate structure is arranged on part of the lower surface of the silicon substrate, the inclined surface of the groove, and part of the top of the groove; the lateral width of the part of the top of the groove not covered by the back field plate structure is 5 to 10 μm; The back field plate structure is connected to the source electrode; there is air as a dielectric between the source and the drain, and the source and the drain cannot be connected through the silicon substrate.
2. The HEMT device with a back field plate structure according to claim 1, characterized in that: The contact line width between the back field plate structure and the GaN epitaxial layer is 5-10 μm.
3. The HEMT device with a back field plate structure according to claim 1, characterized in that: The back field plate structure is a metal film obtained by electron beam evaporation deposition, and has a thickness of 50nm to 2μm.
4. The method for preparing a HEMT device having a back field plate structure according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Using double-sided alignment photolithography technology in the HEMT device, an etching window area is prepared below the gate on the back side of the Si substrate, and the line width in the source and drain direction of the window area is 5 to 10 μm; (2) Using deep silicon etching, the window area is etched to the GaN epitaxial layer. During the etching process, two re-lithography passes are performed. The window is enlarged by 10 to 50 μm toward the source electrode each time, and finally a groove with a right-angle trapezoidal cross section is obtained; (3) using double-sided alignment photolithography technology to prepare a back field plate metal deposition window on the bottom surface of the silicon substrate etched with a groove; (4) Ti / Au metal is deposited on part of the lower surface of the silicon substrate, the inclined surface of the groove, and part of the top surface of the groove to form a back field plate structure.
5. The method for preparing a HEMT device with a back field plate structure according to claim 4, characterized in that: The thickness of the Si substrate is 300-1000 μm.
6. The method for preparing a HEMT device with a back field plate structure according to claim 4, characterized in that: The deposition in step (4) is carried out by electron beam evaporation.