Diamond field effect transistor with n-type slowly-changing doped channel and preparation method of diamond field effect transistor

Abstract

The invention provides a diamond field effect transistor with an n-type slowly-changing doped channel and a preparation method thereof, and the method comprises the steps: enabling a diamond-doped epitaxial layer with the slowly-changing doping concentration to grow on a pretreated substrate through controlling the phosphorus-carbon ratio of high-purity phosphorane and methane gas; and the doping concentration of the diamond-doped epitaxial layer is slowly increased upwards from one side close to the substrate, so that the MOSFET device which is low in ohmic contact resistance and high in output current and is doped with the diamond and has the slowly-changed channel doping concentration is prepared. According to the method, the technological process of secondary growth such as selective doping is avoided, the doping concentration and the thickness of a doping layer can be controlled more accurately, the technological level with higher precision and higher quality is achieved, in addition, diamond epitaxial growth with smaller lattice damage and higher doping efficiency can be achieved through the gaseous doping source in an ionization mode, and the method is suitable for large-scale production. Therefore, two key problems of small output current and high threshold voltage of a doped diamond field effect transistor device are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of field effect transistor power electronic devices, and in particular relates to a diamond field effect transistor with an n-type gradually-varying doped channel and a preparation method thereof. Background Art

[0002] Ultra-wide bandgap semiconductor diamond has the characteristics of high breakdown voltage, high carrier saturation velocity, high carrier mobility, high thermal conductivity, high temperature resistance and radiation resistance. Combined with its outstanding physical properties, diamond can be used as a substrate for high-performance electronic devices or radiation detectors in high voltage, high power and extremely harsh environments, and has great advantages and development potential. Therefore, diamond is known as the ultimate semiconductor material.

[0003] Diamond has been regarded as a semiconductor material that can perfectly replace Si due to its excellent physical properties and as a stable crystal composed of carbon (C), a homologous element of silicon (Si). In logic circuits, the preparation of CMOS inverters is a major application hotspot for Si semiconductor materials. However, for ultra-wide bandgap semiconductor diamond, it is difficult to achieve stable p-type and n-type doping at the same time, which has become a major obstacle to the preparation of CMOS devices.

[0004] At this stage, the most widely used conductivity type in diamond field effect transistors is p-type conductivity dominated by hole carriers. There are currently two main methods to achieve p-type conductivity. One is to treat diamond samples in a hydrogen plasma atmosphere to form hydrogen-terminated diamond, and the other is to incorporate boron atoms during chemical vapor deposition. Hydrogen-terminated diamond can obtain a higher carrier concentration through the transfer doping effect to achieve p-type conductivity applications. In addition to hydrogen-terminated diamond, boron-doped diamond is still the only material that has been successfully used to prepare p-type conductivity field effect transistors. Boron-doped diamond can achieve low-ohmic contact at extremely high doping concentrations, and can also achieve high carrier mobility under low doping conditions and serve as a conductive channel. The corresponding doping concentration can be adjusted according to different application requirements.

[0005] Compared with the application of diamond p-type conductivity, which has been developed, it is more difficult to prepare diamond n-type doping that is sufficient to reach the application level. At present, the mainstream element commonly used for diamond n-type doping is phosphorus (P), but the energy level of P element in the diamond band gap is very deep, reaching 1.57eV (the energy level position of p-type doped B element is 0.37eV). Because of this, it is extremely difficult to activate P element at room temperature after doping it into diamond, and the activation rate is generally less than one thousandth. This problem also seriously restricts the realization and development of n-type diamond field effect transistors and CMOS complementary devices.

[0006] In summary, the current n-type doped diamond field effect transistor has significant problems such as difficulty in realization and extremely low output current density. Therefore, it is of great significance to improve the preparation method of phosphorus-doped diamond epitaxial layer, improve the ohmic contact characteristics of n-type doped diamond and realize the preparation of field effect transistor. Summary of the invention

[0007] In order to solve the above problems existing in the prior art, the present invention provides a diamond field effect transistor with an n-type gradually doped channel and a preparation method thereof. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a diamond field effect transistor with an n-type graded doped channel, comprising:

[0009] S100, selecting a substrate and pre-processing the substrate;

[0010] S200, controlling the phosphorus-carbon ratio of high-purity phosphine and methane gases to grow a diamond-doped epitaxial layer with a slowly varying doping concentration on the pretreated substrate; wherein the doping concentration of the diamond-doped epitaxial layer increases slowly upward from a side close to the substrate;

[0011] S300, preparing a source electrode and a drain electrode on the edge region of the diamond-doped epitaxial layer, and regrowing a gate dielectric layer to cover the source electrode, the drain electrode and the exposed portion of the diamond-doped epitaxial layer;

[0012] S400, preparing a gate electrode on the gate dielectric layer to obtain a diamond field effect transistor with an n-type graded doped channel.

[0013] In a second aspect, the present invention provides a diamond field effect transistor with an n-type graded doped channel, comprising: a substrate, a diamond-doped epitaxial layer, a source electrode, a drain electrode, a gate dielectric layer and a gate electrode; the diamond-doped epitaxial layer is located directly above the substrate, the source electrode and the drain electrode are located on both sides of the diamond-doped epitaxial layer, the gate dielectric layer covers the upper surface and inner side of the source electrode, the upper surface and inner side of the drain electrode, and the upper surface of the diamond-doped epitaxial layer; the gate electrode is located on the gate dielectric layer between the source electrode and the drain electrode;

[0014] Wherein, the doping concentration of the diamond-doped epitaxial layer increases slowly from the side close to the substrate to the side close to the gate dielectric layer.

[0015] Beneficial effects:

[0016] 1. Effectively reduce the process difficulty. The present invention adjusts the phosphorus-carbon ratio by adjusting the gas flow rate during the growth of the diamond-doped epitaxial layer, thereby achieving an extremely thin, high-concentration, heavily doped layer on the diamond surface required for a good ohmic contact and a lower-concentration lightly doped layer required for the channel layer, avoiding the process flow of secondary growth such as selective doping.

[0017] 2. Improved process parameter accuracy. The present invention uses a gas doping source. Compared with solid state, the doping effect can be regulated by adjusting the gas flow rate, which can more accurately control the doping concentration and doping layer thickness, achieving a higher precision and higher quality process level.

[0018] 3. Reduced lattice distortion and lattice damage. Compared with the solid-state doping atomic heterothermal diffusion method, the gaseous doping source of the present invention can achieve diamond epitaxial growth with less lattice damage and higher doping efficiency in an ionized manner.

[0019] 4. The present invention realizes diamond n-type body conductivity through the method of slowly phosphorus-doped diamond epitaxial layer and high-temperature annealing activation, and prepares n-type slowly doped channel diamond field effect transistor based on this, and solves the two key problems of low output current and high threshold voltage of doped diamond field effect transistor devices, making doped diamond a big step forward in the application of n-type slowly doped channel diamond field effect transistors.

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The present invention provides a flow chart of a method for preparing a diamond field effect transistor with an n-type gradually doped channel;

[0022] Figure 2a-2e A schematic diagram of a process for preparing a diamond field effect transistor with an n-type gradually doped channel provided by the present invention;

[0023] Figure 3 A diamond field effect transistor with an n-type gradually-doped channel provided by the present invention;

[0024] Figure 4 Schematic diagram of the structure of diamond material with gradually varying doping concentration. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0026] Embodiment 1

[0027] Combination Figure 1 and Figure 2a-2e , Figure 1 The present invention provides a flow chart of a method for preparing a diamond field effect transistor with an n-type gradually doped channel. Figure 2a-2e The present invention provides a process schematic diagram of a method for preparing a diamond field effect transistor with an n-type gradually doped channel. The present invention provides a method for preparing a diamond field effect transistor with an n-type gradually doped channel, comprising:

[0028] S100, selecting a substrate and pre-processing the substrate.

[0029] like Figure 2a As shown, Figure 2a The present invention selects CVD epitaxial intrinsic diamond as a substrate; the substrate is cleaned in a strong acid mixed solution, acetone, ethanol, and deionized water at 200° C. in sequence; the cleaned substrate is placed in a microwave plasma chemical vapor deposition MPCVD system, and then pre-treated by hydrogen plasma etching to obtain a pre-treated substrate.

[0030] Of course, the material of the intrinsic diamond of the present invention includes but is not limited to single crystal diamond, and the thickness is 300-500 μm.

[0031] S200, by controlling the phosphorus-carbon ratio of high-purity phosphine and methane gases, a diamond-doped epitaxial layer with a gradually varying doping concentration is grown on the pretreated substrate, such as Figure 2b As shown; wherein, the doping concentration of the diamond-doped epitaxial layer 2 increases slowly from the side close to the substrate upward; the doping elements of the diamond-doped epitaxial layer 2 are but not limited to one or more of phosphorus, sulfur, and oxygen, and the thickness of the diamond-doped epitaxial layer 2 is 50-200nm.

[0032] In this step, high-purity phosphine and methane gases can be introduced into the chamber of the MPCVD system to provide the boron source and carbon source required for diamond epitaxial growth; the gas flow rates of the high-purity phosphine and the methane gases are adjusted to control the phosphorus-carbon ratio to grow a diamond-doped epitaxial layer with a slowly varying doping concentration on the pretreated substrate.

[0033] S300, preparing a source electrode 3 and a drain electrode 4 on the edge region of the diamond-doped epitaxial layer, such as Figure 2c As shown, the gate dielectric layer 5 is regrown to cover the source electrode 3, the drain electrode 4 and the exposed portion of the diamond-doped epitaxial layer 2, as shown in FIG. Figure 2d As shown;

[0034] The material of the source electrode and the drain electrode includes one or more of Ti, Pt, and Au, and the thickness of the source electrode and the drain electrode is 100-200 nm. For example, the material of the drain electrode can be Ti / Au, with a thickness of 20 / 100 nm.

[0035] S400, preparing a gate electrode 6 on the gate dielectric layer to obtain a diamond field effect transistor with an n-type graded doped channel, such as Figure 2e shown.

[0036] The material of the gate dielectric layer includes SiO 2 、Al 2 O 3 、MoO 3 , HfO 2 、HfAlO 2 One or more of the above, the thickness of the gate dielectric layer is 20-50 nm. For example, the gate dielectric layer 5 is 20 nm thick Al 2 O 3 .

[0037] The present invention adjusts the phosphorus-carbon ratio by adjusting the gas flow rate during the growth of the diamond-doped epitaxial layer, and at the same time realizes the extremely thin high-concentration heavily doped layer on the diamond surface required for good ohmic contact, and the lightly doped layer with a lower concentration required for the channel layer, avoiding the process flow of secondary growth such as selective doping. In addition, the present invention adopts a gas doping source. Compared with the solid state, by adjusting the gas flow rate to control the doping effect, the doping concentration and the thickness of the doping layer can be more accurately controlled, and a higher precision and higher quality process level can be achieved. Compared with the solid-state doping atomic heat diffusion method, the gaseous doping source of the present invention can achieve diamond epitaxial growth with less lattice damage and higher doping efficiency in an ionized manner. The present invention realizes diamond n-type body conductivity by slowly changing phosphorus doped diamond epitaxial layer and high temperature annealing activation method, and prepares devices based on this, and at the same time solves the two key problems of low output current and high threshold voltage of doped diamond field effect transistor devices, making doped diamond a big step forward in the application of field effect transistor devices.

[0038] Combination Figure 3 and Figure 4 , Figure 3 The present invention provides a diamond field effect transistor with an n-type gradually doped channel. Figure 4 The structure diagram of the diamond material with gradually varying doping concentration. The diamond field effect transistor with n-type gradually varying doped channel of the present invention comprises: a substrate 1, a diamond doped epitaxial layer 2, a source electrode 3, a drain electrode 4, a gate dielectric layer 5 and a gate electrode 6; the diamond doped epitaxial layer 2 is located directly above the substrate 1, the source electrode 3 and the drain electrode 4 are located on both sides of the diamond doped epitaxial layer 2, the gate dielectric layer 5 covers the upper surface and inner side of the source electrode 3, the upper surface and inner side of the drain electrode 4, and the upper surface of the diamond doped epitaxial layer 2; the gate electrode 6 is located on the gate dielectric layer 5 between the source electrode 3 and the drain electrode 4;

[0039] The source electrode 3, the drain electrode 4, the gate dielectric layer 5 and the gate electrode 6 of the present invention form a ring-gate structure.

[0040] refer to Figure 4 The doping concentration of the diamond-doped epitaxial layer 2 increases slowly from the side close to the substrate 1 to the side close to the gate dielectric layer 5. The doping concentration of the diamond-doped epitaxial layer 2 increases slowly by controlling the phosphorus-carbon ratio of high-purity phosphine and methane gas.

[0041] The material of the substrate 1 of the present invention includes but is not limited to single crystal diamond, with a thickness of 300-500 μm. The thickness of the diamond epitaxial layer 2 with a graded doping concentration is 50-80 nm. The materials of the source electrode 3 and the drain electrode 4 include one or more of Ti, Pt, and Au, with a thickness of 100-200 nm. For example, the material of the drain electrode 4 is Ti / Au, with a thickness of 20 / 100 nm. The material of the gate dielectric layer 5 includes SiO 2 、Al 2 O 3 、MoO 3 , HfO 2 、HfAlO 2 One or more of the above, the thickness of the gate dielectric layer 5 is 20-50 nm, for example, the gate dielectric layer 5 is 20 nm thick Al 2 O 3 .

[0042] The present invention provides a diamond field effect transistor with an n-type slowly doped channel. By adjusting the gas flow rate during the growth of the diamond doped epitaxial layer, the phosphorus-carbon ratio is regulated, and the extremely thin high-concentration heavily doped layer on the diamond surface required for good ohmic contact and the lightly doped layer with a lower concentration required for the channel layer are achieved at the same time, thereby avoiding the process flow of secondary growth such as selective doping. In addition, the present invention adopts a gas doping source. Compared with the solid state, the doping effect can be regulated by adjusting the gas flow rate, and the doping concentration and the thickness of the doped layer can be controlled more accurately, achieving a higher precision and higher quality process level. Compared with the solid-state doped atomic impurity heat diffusion method, the gaseous doping source of the present invention can achieve diamond epitaxial growth with less lattice damage and higher doping efficiency in an ionized manner. The present invention realizes diamond n-type body conductivity by slowly changing phosphorus doped diamond epitaxial layer and high temperature annealing activation method, and prepares devices based on this, while solving the two key problems of low output current and high threshold voltage of doped diamond field effect transistor devices, making doped diamond a big step forward in the application of field effect transistor devices.

[0043] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for preparing a diamond field effect transistor with an n-type graded doped channel, characterized in that: include: S100, selecting a substrate and pre-processing the substrate; S200, controlling the phosphorus-carbon ratio of high-purity phosphine and methane gases to grow a diamond-doped epitaxial layer with a slowly varying doping concentration on the pretreated substrate; wherein the doping concentration of the diamond-doped epitaxial layer increases slowly upward from a side close to the substrate; S300, preparing a source electrode and a drain electrode on the edge region of the diamond-doped epitaxial layer, and regrowing a gate dielectric layer to cover the source electrode, the drain electrode and the exposed portion of the diamond-doped epitaxial layer; S400, preparing a gate electrode on the gate dielectric layer to obtain a diamond field effect transistor with an n-type graded doping channel.

2. The method for preparing a diamond field effect transistor with an n-type graded doped channel according to claim 1, characterized in that: S100 includes: Select CVD epitaxial intrinsic diamond as substrate; The substrate is cleaned in a strong acid mixed solution, acetone, ethanol, and deionized water at 200° C. in sequence; The cleaned substrate is placed in a microwave plasma chemical vapor deposition MPCVD system, and then pre-treated by hydrogen plasma etching to obtain a pre-treated substrate.

3. The method for preparing a diamond field effect transistor with an n-type graded doped channel according to claim 1, characterized in that: S200 includes: High-purity phosphine and methane gases are introduced into the chamber of the MPCVD system to provide boron and carbon sources required for diamond epitaxial growth; The gas flow rates of the high-purity phosphine and the methane gas are adjusted to control the phosphorus-carbon ratio, so as to grow a diamond-doped epitaxial layer with a gradually varying doping concentration on the pretreated substrate.

4. The method for preparing a diamond field effect transistor with an n-type graded doped channel according to claim 2, characterized in that: The intrinsic diamond comprises single crystal diamond and has a thickness of 300-500 μm.

5. The method for preparing a diamond field effect transistor with an n-type graded doped channel according to claim 1, characterized in that: The doping elements of the diamond-doped epitaxial layer include one or more of phosphorus, sulfur and oxygen, and the thickness of the diamond-doped epitaxial layer is 50-200 nm.

6. The method for preparing a diamond field effect transistor with an n-type graded doped channel according to claim 1, characterized in that: The source electrode and the drain electrode are made of one or more materials selected from the group consisting of Ti, Pt, and Au, and have a thickness of 100-200 nm.

7. The method for preparing a diamond field effect transistor with an n-type graded doped channel according to claim 1, characterized in that: The material of the gate dielectric layer includes one or more of SiO2, Al2O3, MoO3, HfO2, and HfAlO2, and the thickness of the gate dielectric layer is 20-50 nm.

8. A diamond field effect transistor with an n-type graded doped channel, characterized in that: include: A substrate (1), a diamond-doped epitaxial layer (2), a source electrode (3), a drain electrode (4), a gate dielectric layer (5) and a gate electrode (6); the diamond-doped epitaxial layer (2) is located directly above the substrate (1); the source electrode (3) and the drain electrode (4) are located on both sides of the diamond-doped epitaxial layer (2); the gate dielectric layer (5) covers the upper surface and inner side of the source electrode (3), the upper surface and inner side of the drain electrode (4), and the upper surface of the diamond-doped epitaxial layer (2); and the gate electrode (6) is located on the gate dielectric layer (5) between the source electrode (3) and the drain electrode (4); The doping concentration of the diamond-doped epitaxial layer (2) increases slowly from a side close to the substrate (1) to a side close to the gate dielectric layer (5).

9. The diamond field effect transistor with n-type graded doped channel according to claim 8, characterized in that: The doping concentration of the diamond-doped epitaxial layer (2) increases slowly, which is achieved by controlling the phosphorus-carbon ratio of high-purity phosphine and methane gases.

10. The diamond field effect transistor with n-type graded doped channel according to claim 8, characterized in that: The doping elements of the diamond-doped epitaxial layer include one or more of phosphorus, sulfur and oxygen, and the thickness of the diamond-doped epitaxial layer is 50-200 nm.

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