CN101814434A - Method for manufacturing nitrogen face polar AlN/AlInN composite back barrier gallium nitride field effect transistor - Google Patents

Abstract

The invention discloses a method for manufacturing a nitrogen-face polar AlN/AlInN composite back barrier gallium nitride field effect transistor. The steps of the method include sequentially growing a nitrogen-face polar GaN buffer layer on a substrate, AlInN modulation doping layer, δ-doped layer, AlInN back barrier isolation layer, AlN back barrier isolation layer, GaN channel layer and AlGaN front barrier layer; a high-density electron gas is generated by modulating the doped AlN/AlInN composite back barrier layer and a strong back potential barrier to strengthen the two-dimensional characteristics of the channel electron gas, and make a high-performance nitrogen surface polar field effect transistor. The invention can increase the electron gas density and thicken the back potential barrier, strengthen the quantum confinement of the back potential barrier and reduce the strain and defect density of the potential barrier layer; use the strongly modulated doping provided by the composite back potential barrier to carry out channel well and front barrier The optimized design of the barrier can not only improve the quantum confinement of the front barrier, improve the transconductance and linear characteristics of the device, but also optimize the performance of the Schottky barrier and ohmic contact; it is suitable for the research of high power, high PAE and millimeter wave high High-frequency high-reliability field effect tube.

Description

A method for manufacturing nitrogen-face polar AlN/AlInN composite back barrier gallium nitride field effect transistor

technical field

The invention relates to a method for manufacturing a semiconductor device, in particular to a method for manufacturing a nitrogen-face polarity AlN/AlInN compound back barrier gallium nitride field effect transistor. The method is to construct a high-density, strong two-dimensional electron gas by using the polar back potential barrier of the nitrogen face, and is used to manufacture high-power, high-reliability gallium nitride field effect transistors.

Background technique

Nitride is a polar material with two polarities of Ga face and N face. Most of the field effect transistors currently developed use Ga-face polarity. In Ga surface polar materials, there are positively polarized charges and large energy band steps on the AlGaN/GaN heterointerface, which produces a high-density two-dimensional electron gas, which makes the output power of GaN FETs higher than that of GaAs FETs. One order of magnitude. However, this strong polarized charge also brings some negative effects while generating a high-density electron gas. Field effect transistors require high potential barriers to be established at both ends of the channel well to strengthen the quantum confinement of the channel well and the two-dimensional characteristics of the electron gas. However, when the potential barrier on the back of the channel well is constructed, a layer of positively polarized charges is also generated at the end of the back barrier layer to form a second sub-channel well, which generates parallel conductance and keeps the channel clamped. At present, many foreign research institutes are studying another kind of polarity, that is, nitrogen surface polar materials. Under the polarity of the nitrogen surface, the back barrier terminal generates negative polarized charges, which raise the potential barrier without forming a sub-channel well, which solves the problem of the back barrier. However, under this polarity, negatively polarized charges appear on the AlGaN/GaN interface, and two-dimensional electron gas cannot be generated. To this end, it is necessary to add strong forced doping in the back barrier to generate a two-dimensional electron gas. In order to strengthen the back barrier and improve modulation doping efficiency, everyone uses AlN barrier and strong δ doping. However, there is a large lattice mismatch between AlN and GaN, and it is difficult to grow a pseudo-AlN layer larger than 3nm on GaN. This kind of thin AlN barrier layer plus δ-doped heterostructure not only has high stress, high growth difficulty, and many defects, but also the thin barrier is difficult to prevent high-energy electrons in the channel from tunneling to the buffer layer, and the modulation doping efficiency is low. It is necessary to design a very wide GaN channel well to increase the electron gas density. As the GaN channel well width increases, the two-dimensional characteristics of the electron gas decrease, and the transconductance of the field effect transistor decreases. In addition, the pre-growth barrier on the channel layer reduces the electron gas density. Improvement in device performance is thus hindered. In order to improve the modulation doping efficiency in the back barrier, a new back barrier structure must be designed using the energy band tailoring method. Recently, many foreign authors have studied the AlInN potential barrier. Large In atoms increase the lattice constant, which can match the GaN lattice at a large Al composition ratio. When the Al composition ratio is 0.83, it just matches the GaN lattice perfectly, eliminating strain. The thickness of the back barrier can be significantly increased with this new lattice-matched material. However, there is a large energy band gap between AlInN and GaN channels, and doping in the AlInN barrier layer can improve the efficiency of modulation doping, thereby generating a strong two-dimensional electron gas in the N-face heterojunction. On the other hand, the field effect transistor relies on the gate electrode to control the channel conductance; the gate electrode is regulated through the front potential barrier. In this way, the front barrier still plays a crucial role in the device operation. In order to increase the electron gas density in the current design of the nitrogen-faced polar heterostructure, the front barrier cannot be taken into account, and only a simple wide GaN channel well is used. This not only increases the leakage current of the gate electrode, but also significantly reduces the transconductance and linearity characteristics of the device. In addition, the electron wave function in the channel well easily penetrates to the surface, tunneling to the surface state and causing the current collapse. Using the AlN/AlInN composite back barrier can achieve high modulation doping efficiency, which is enough to generate a strong two-dimensional electron gas; thus, the front barrier can be optimized to further improve the performance of the field effect transistor.

Contents of the invention

Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a method for manufacturing a nitrogen-face polar AlN/AlInN compound back barrier gallium nitride field effect transistor, which uses a nitrogen-face polar AlN/AlInN composite Potential barrier to build the back barrier, increase the width of the back barrier, reduce the strain and defects in the back barrier, improve the efficiency of modulation doping and the electron gas density in the channel; at the same time, optimize the design of the front barrier of the channel, Increase the height of the front barrier, reduce the well width of the channel well, strengthen the quantum confinement of the front barrier, improve the control of the gate electrode on the conductance of the channel, and prevent the channel electrons from tunneling to the surface state. In this way, the transport performance of channel electrons can be improved, the transconductance and linear performance of the device can be improved, and the current collapse can be suppressed.

Technical solution: In order to achieve the above purpose, a method for manufacturing a nitrogen-face polar AlN/AlInN composite back barrier gallium nitride field effect transistor according to the present invention comprises the following steps: 1) sequentially growing a nitrogen face on a substrate Polar GaN buffer layer and AlInN modulated doped layer matched with GaN lattice; 2) On the AlInN modulated doped layer, δ-doped layer, AlInN back barrier isolation layer and AlN back barrier isolation layer are grown sequentially to form AlN /AlInN composite back barrier; 3) GaN channel layer and AlGaN front barrier layer are grown on the AlN/AlInN composite back barrier; 4) AlGaN front barrier layer is etched directly on the GaN channel layer by dry process Make source and drain ohmic contacts on top; 5) Make Schottky barriers on the AlGaN front barrier layer, use the energy band tailoring method to strengthen the quantum confinement of the AlGaN front barrier layer, increase the height and width of the Schottky barrier and reduce the gate flow, improving transconductance and linearity of device operation.

The AlInN modulated doped layer has a thickness of 10-40 nm.

The thickness of the AlInN back barrier isolation layer is 4nm.

The AlInN back barrier is grown under the AlN back barrier isolation layer. Using the matching characteristics of the AlInN lattice and the GaN lattice, the back barrier can be widened to prevent the high-energy electrons in the channel from tunneling to the buffer layer and causing leakage current; It can suppress the collapse of the back barrier caused by local click-through of the thin AlN back barrier during the radio frequency operation of the device, and improve the reliability of the device.

Setting a thick AlInN back barrier layer under the delta-doped layer can achieve modulation doping by doping in the AlInN layer, increase the modulation doping strength, and increase the electron gas density in the channel. Optimize the design of the thickness of the AlN back barrier isolation layer and the AlInN back barrier isolation layer, the doping intensity of the δ-doped layer, and the thickness and doping concentration of the AlInN modulation doped layer, which can reduce the back barrier under the premise of achieving a high density electron gas. Strain and defect density in the potential barrier, improving channel well material quality and electron gas transport properties.

Under the premise of increasing the channel electron gas density, the thickness of the GaN channel layer and the Al composition ratio and thickness of the AlGaN front barrier layer can be optimally designed, the energy bands of the channel layer and the front barrier can be tailored, and the front barrier can be strengthened. Quantum confinement improves the two-dimensional properties of the electron gas. Fabricating Schottky barriers on the AlGaN front barrier layer can increase the height of the barrier and increase the width of the front barrier, which can not only reduce the gate current, but also improve the control strength and transconductance of the gate electrode to the channel conductance; The gate capacitance and transconductance remain unchanged under the dynamic change of gate voltage, which improves the linearity of device operation.

When making source and drain ohmic contacts, the front barrier layer of AlGaN is etched by dry process, and the metal contact is directly made on the GaN channel layer. The low barrier height of GaN and the shortened electrode-electron gas peak spacing are used to increase the tunneling current and reduce the ohmic contact resistance.

Beneficial effects: A method for manufacturing a nitrogen-face polar AlN/AlInN composite back barrier gallium nitride field effect transistor of the present invention, by combining the AlN back barrier isolation layer and the AlInN layer into a composite back barrier, not only can widen the The back potential barrier improves the back barrier structure and enhances the two-dimensional characteristics of the electron gas, and the thick AlInN layer with lattice matching can provide an environment for strongly modulated doping and increase the intensity of modulated doping. At the same time, the present invention also has the following advantages: 1) It can significantly improve the margin of barrier design; 2) It can reduce the AlN layer thickness and δ doping intensity of lattice mismatch to reduce structural defects and trap density, and improve the channel electron density. The transport characteristics of the gas improve the reliability of the device; 3) The energy band can be tailored through the optimized design of the front barrier, and the quantum confinement effect of the front barrier can be strengthened; 4) The respective optimizations for the ohmic contact and the Schottky barrier are constructed The potential barrier structure reduces gate current and ohmic contact resistance, and makes a high-performance N-surface field effect transistor.

Description of drawings

The accompanying drawing is a material structure diagram of the nitrogen-face polar AlN/AlInN compound back barrier gallium nitride field effect transistor of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in the figure, on the substrate 1, a GaN buffer layer 2 with a nitrogen plane polarity, an AlInN modulation doped layer 3, a delta doped layer 4, an AlInN back barrier isolation layer 5 and an AlN back barrier isolation layer 6 are sequentially grown , forming an AlN/AlInN compound back potential barrier; and then growing a GaN channel layer 7 and an AlGaN front barrier layer 8 on the compound back potential barrier. Optimize the thickness of the AlInN modulation doped layer 3 to achieve thick back barrier and high-intensity modulation doping; optimize the design of the delta doping intensity in the delta doping layer 4 and the modulation doping of the AlInN back barrier to produce high density Two-dimensional electron gas; optimize the thickness of the AlInN back barrier isolation layer 5 and AlN back barrier isolation layer 6, so that the channel electron gas is far away from the ionized impurity center, and reduce the ionized impurity scattering and crystal lattice experienced by the channel electron gas Lattice strain and defects caused by mismatched AlN layer; optimize the thickness of the GaN channel layer 7 and the Al composition ratio and thickness of the AlGaN front barrier layer 8 to strengthen the quantum confinement and Schottky of the front barrier of the channel well Potential barrier and ohmic contact performance, to achieve the designed transconductance and pinch-off voltage.

In the device manufacturing process, the AlGaN front barrier layer 8 on the source and drain ohmic contacts is first dug out by photolithography and etching technology, and the ohmic contact is directly made on the GaN channel layer 7, taking advantage of the low potential barrier and shortening of GaN. The distance between the ohmic electrode metal and the electron gas increases the tunneling current and reduces the ohmic contact resistance. Then, a Schottky barrier is formed on the AlGaN front barrier layer 8 . The AlGaN high potential barrier is used to reduce the gate current, strengthen the quantum confinement of the channel well and the control of the channel conductance by the gate electrode, and prevent the channel electrons from tunneling to the surface state to cause current collapse. Finally, a high-quality nitrogen-face polar AlN/AlInN compound back barrier gallium nitride field effect transistor with a high and thick back barrier is manufactured.

Example 1:

A GaN buffer layer 2 with a nitrogen plane polarity is grown on a substrate 1, and an Al _0.83 In _0.17 N modulated doped layer 3 with a thickness of 10 nm and a lattice match with GaN is grown on the N plane GaN buffer layer 2 with a doping concentration of 1 *10 ¹⁹ cm ^-3 . Then grow a delta-doped layer 4 with a doping concentration of 1.5*10 ¹³ cm ^{-2 ,} a 4nm-thick non-doped Al _0.83 In _0.17 N back barrier isolation layer 5 and a 2nm-thick non-doped AlN isolation layer 6. Constitute the AlN/AlInN composite back potential barrier. Then grow a 10nm thick undoped GaN channel layer 7 and a 10nm thick undoped Al _0.3 Ga _0.7 N front barrier layer 8 on the composite back barrier. Self-consistently solving the Schrödinger equation and Poisson equation, the channel electron gas density is 13.297×10 ¹² cm ^-2 , and the pinch-off voltage is -5V. After the front potential barrier layer 8 is removed, the distance from the gate electrode to the channel electron gas is less than 10nm, and it is easy to make low-resistance source and drain ohmic electrodes.

Example 2:

A 20nm-thick Al _0.83 In _0.17 N modulation doped layer 3 that matches the GaN lattice is grown on the N-face GaN buffer layer 2 with a doping concentration of 6*10 ¹⁸ cm ^-3 . Then grow a delta-doped layer 4 with a doping concentration of 1*10 ¹³ cm ^{-2 ,} a 4nm-thick undoped Al _0.83 In _0.17 N back barrier isolation layer 5 and a 2nm-thick undoped AlN isolation layer 6. Constitute the AlN/AlInN composite back potential barrier. Then grow a 10nm thick undoped GaN channel layer 7 and a 10nm thick undoped Al _0.3 Ga _0.7 N front barrier layer 8 on the composite back barrier. Self-consistently solving the Schrödinger equation and Poisson equation, the channel electron gas density is 11.045×10 ¹² cm ^-2 , and the pinch-off voltage is -4.1V. After the front potential barrier layer 8 is removed, the distance from the gate electrode to the channel electron gas is less than 10nm, and it is easy to make low-resistance source and drain ohmic electrodes.

Example 3:

On the substrate 1, a GaN buffer layer 2 with a nitrogen plane polarity is grown sequentially, and a 40nm-thick Al _0.83 In _0.17 N modulated doped layer 3 matching the GaN lattice is grown on the N plane GaN buffer layer 2 with a doping concentration of 4*10 ¹⁸ cm ^-3 . Then grow a delta-doped layer 4 with a doping concentration of 7*10 ¹² cm ^{-2 ,} a 4nm-thick undoped Al _0.83 In _0.17 N back barrier isolation layer 5 and a 2nm-thick undoped AlN isolation layer 6. Constitute the AlN/AlInN composite back potential barrier. Then grow a 10nm thick undoped GaN channel layer 7 and a 10nm thick undoped Al _0.3 Ga _0.7 N front barrier layer 8 on the composite back barrier. Self-consistently solving the Schrödinger equation and Poisson equation, the channel electron gas density is 13.017×10 ¹² cm ^-2 , and the pinch-off voltage is -4.9V. After the front potential barrier layer 8 is removed, the distance from the gate electrode to the channel electron gas is less than 10nm, and it is easy to make low-resistance source and drain ohmic electrodes.

Example 4:

On the substrate 1, a GaN buffer layer 2 with a nitrogen plane polarity is sequentially grown, and a 35nm-thick Al _0.83 In _0.17 N modulated doped layer 3 matching the GaN lattice is grown on the N plane GaN buffer layer 2 with a doping concentration of 4*10 ¹⁸ cm ^-3 . Then grow a delta-doped layer 4 with a doping concentration of 1*10 ¹³ cm ^{-2 ,} a 4nm-thick undoped Al _0.83 In _0.17 N back barrier isolation layer 5 and a 2nm-thick undoped AlN isolation layer 6. Constitute the AlN/AlInN composite back potential barrier. Then grow a 10nm thick undoped GaN channel layer 7 and an 8nm thick undoped Al _0.3 Ga _0.7 N front barrier layer 8 on the composite back barrier. Self-consistently solving the Schrödinger equation and Poisson equation, the channel electron gas density is 13.847×10 ¹² cm ^-2 , and the pinch-off voltage is -4.6V. After the front potential barrier layer 8 is removed, the distance from the gate electrode to the channel electron gas is less than 10nm, and it is easy to make low-resistance source and drain ohmic electrodes.

Example 5:

On the substrate 1, a nitrogen-plane polarity GaN buffer layer 2 is grown sequentially, and a 25nm-thick Al _0.83 In _0.17 N modulated doped layer 3 matching the GaN lattice is grown on the N-plane GaN buffer layer 2, with a doping concentration of 6*10 ¹⁸ cm ³ . Then grow a delta-doped layer 4 with a doping concentration of 1.4*10 ¹³ cm ^{-2 ,} a 4nm-thick undoped Al _0.83 In _0.17 N back barrier isolation layer 5 and a 2nm-thick undoped AlN isolation layer 6. Constitute the AlN/AlInN composite back potential barrier. Then grow an 8nm-thick undoped GaN channel layer 7 and an 8nm-thick undoped Al _0.3 Ga _0.7 N front barrier layer 8 on the composite back barrier. Self-consistently solving the Schrödinger equation and Poisson equation, the channel electron gas density is 16.331×10 ¹² cm ^-2 , and the pinch-off voltage is -4.9V. After the front potential barrier layer 8 is removed, the distance from the gate electrode to the channel electron gas is less than 8nm, and it is easy to make low-resistance source and drain ohmic electrodes.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications are also possible. It should be regarded as the protection scope of the present invention.

Claims (3)

1. A method for manufacturing a nitrogen-face polar AlN/AlInN compound back barrier gallium nitride field effect transistor, characterized in that it comprises the following steps: 1) On the substrate (1), sequentially grow a nitrogen plane polarity GaN buffer layer (2) and an AlInN modulation doped layer (3) that matches the GaN lattice; 2) On the AlInN modulation doped layer (3), grow the δ-doped layer (4), the AlInN back barrier isolation layer (5) and the AlN back barrier isolation layer (6) in sequence to form an AlN/AlInN composite back barrier ; 3) growing a GaN channel layer (7) and an AlGaN front barrier layer (8) on the AlN/AlInN composite back barrier; 4) making source and drain ohmic contacts directly on the GaN channel layer (7) after etching the AlGaN front barrier layer (8) by a dry process; 5) Fabricate a Schottky barrier on the AlGaN front barrier layer (8), use the energy band clipping method to strengthen the quantum confinement of the AlGaN front barrier layer (8), increase the height and width of the Schottky barrier and reduce the gate current, Improves transconductance and linearity of device operation. 2. A method for manufacturing a nitrogen-face polarity AlN/AlInN compound back barrier gallium nitride field effect transistor according to claim 1, characterized in that: the thickness of the AlInN modulation doped layer (3) is 10 ~40nm. 3. A method for manufacturing a nitrogen-face polarity AlN/AlInN compound back barrier gallium nitride field effect transistor according to claim 1, characterized in that: the thickness of the AlInN back barrier isolation layer (5) is 4nm.

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