Diamond variable threshold field effect transistor with adjustable channel width and method of fabrication

Abstract

The application discloses a diamond variable threshold field effect transistor with adjustable channel width, comprising an N-type diamond substrate, a P-type diamond epitaxial layer, a P+ type diamond epitaxial layer, a source electrode, a drain electrode, a gate dielectric layer, a gate electrode and a back electrode, wherein the P-type diamond epitaxial layer is arranged on the upper surface of the N-type diamond substrate; the P+ type diamond epitaxial layer is arranged on the left and right sides of the upper surface of the P-type diamond epitaxial layer respectively, the source electrode and the drain electrode are arranged on the P+ type diamond epitaxial layer on the left and right sides respectively, and the P+ type diamond epitaxial layer forms ohmic contact with the source electrode and the drain electrode above it respectively; the gate dielectric layer is arranged on the upper surface of the P-type diamond epitaxial layer which is not covered by the P+ type diamond epitaxial layer, and the gate electrode is arranged on the upper surface of the gate dielectric layer; and the back electrode is arranged on the lower surface of the N-type diamond substrate. The diamond field effect transistor has the advantages of high thermal conductivity, high radiation resistance, flexible selectivity of depletion type and enhancement type and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor field effect transistor, and particularly relates to a diamond variable threshold field effect transistor with adjustable channel width and a preparation method, so as to realize controllable conversion of the diamond field effect transistor between depletion type and enhancement type. BACKGROUND

[0002] As a kind of ultra-wide band gap semiconductor material, diamond is called "ultimate semiconductor", which has the advantages of high breakdown voltage, high thermal conductivity, high carrier mobility and strong anti-radiation capability, and has great potential in high-temperature, high-frequency and high-power electronic device applications. Diamond, like silicon material, belongs to four-group semiconductor material, and n-type and p-type semiconductor material is realized by doping boron and phosphorus elements.

[0003] At present, diamond boron-doped and phosphorus-doped field effect transistor devices have been widely reported. However, due to the difficulty in regulating the channel carrier concentration, the devices reported at present are all depletion type. Enhancement type device has the advantages of low power consumption and high safety. Diamond enhancement type field effect transistor is also widely studied, but the existing method is to realize it by reducing the doping concentration, changing the gate metal work function and the type of gate dielectric. This method is difficult to realize diamond enhancement type device, has high cost and poor process repeatability. SUMMARY

[0004] In order to solve the above problems existing in the prior art, the present application provides a diamond variable threshold field effect transistor with adjustable channel width and a preparation method. The technical problem to be solved by the present application is realized by the following technical scheme:

[0005] One aspect of the present application provides a diamond variable threshold field effect transistor with adjustable channel width, comprising an N-type diamond substrate, a P-type diamond epitaxial layer, a P+ type diamond epitaxial layer, a source electrode, a drain electrode, a gate dielectric layer, a gate electrode and a back electrode, wherein,

[0006] The P-type diamond epitaxial layer is arranged on the upper surface of the N-type diamond substrate; the P+ type diamond epitaxial layer is arranged on the upper surface of the P-type diamond epitaxial layer on both sides, respectively; the source electrode and the drain electrode are arranged on the P+ type diamond epitaxial layer on both sides, respectively; the P+ type diamond epitaxial layer forms ohmic contact with the source electrode and the drain electrode above it, respectively;

[0007] The gate dielectric layer is arranged on the upper surface of the P-type diamond epitaxial layer which is not covered by the P+ type diamond epitaxial layer, and the gate electrode is arranged on the upper surface of the gate dielectric layer and located between the source electrode and the drain electrode;

[0008] The back electrode is arranged on the lower surface of the N-type diamond substrate.

[0009] In one embodiment of the present application, the doping concentration of the P-type diamond epitaxial layer is 1×10 15 ~ 1×10 16 cm -3 ; the doping concentration of the P+ type diamond epitaxial layer is 1×10 19 ~ 1×10 21 cm -3 .

[0010] In one embodiment of the present application, the doping element of the N-type diamond substrate is boron, and the doping elements of the P-type diamond epitaxial layer and the P+ type diamond epitaxial layer are both phosphorus.

[0011] In one embodiment of the present application, the thickness of the N-type diamond substrate is 200-300 μm, and the thickness of the P-type diamond epitaxial layer and the P+ type diamond epitaxial layer is both 1-5 μm.

[0012] In one embodiment of the present application, the source electrode and the drain electrode both adopt Au material, and the thickness is 50-100 nm.

[0013] In one embodiment of the present application, the spacing between the source electrode and the drain electrode is 2-10 μm.

[0014] In one embodiment of the present application, the gate electrode adopts Al\Au laminated metal, wherein the Al metal layer is below the Au metal layer, the thickness of the Al metal layer is 10-20 nm, and the thickness of the Au metal layer is 40-100 nm.

[0015] In one embodiment of the present application, the back electrode adopts Au\Ti laminated metal, wherein the Au metal layer is below the Ti metal layer, the thickness of the Au metal layer is 40-100 nm, and the thickness of the Ti metal layer is 10-20 nm.

[0016] Another aspect of the present application provides a preparation method of a diamond variable threshold field effect transistor with adjustable channel width, for preparing the diamond variable threshold field effect transistor with adjustable channel width in any of the above embodiments, and the preparation method comprises:

[0017] S1: obtaining an N-type diamond substrate;

[0018] S2: growing a P-type diamond epitaxial layer and a P+ type diamond epitaxial layer on the upper surface of the N-type diamond substrate in sequence;

[0019] S3: etching the P+ type diamond epitaxial layer so as to only reserve the P+ type diamond epitaxial layer in the source region and the drain region;

[0020] a P- type diamond epitaxial layer;

[0021] S4: depositing a source electrode and a drain electrode on the P+ type diamond epitaxial layer of the source region and the drain region respectively;

[0022] S5: depositing a gate dielectric layer on the P- type diamond epitaxial layer;

[0023] S6: depositing a gate electrode above the gate dielectric layer, so that the gate electrode is located between the source electrode and the drain electrode;

[0024] S7: depositing a back electrode on the lower surface of the N type diamond substrate.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] 1. The present application grows a P- type diamond epitaxial layer and a P+ type diamond epitaxial layer on an n type doped diamond substrate, uses the P- type diamond epitaxial layer as a device channel, and the P+ type diamond epitaxial layer forms an ohmic contact of the device. A back electrode is made below the n type substrate. The channel width is adjusted by adjusting the height of the n-p Schottky barrier, so as to realize a diamond field effect transistor with adjustable threshold voltage, and the transition from depletion type to enhancement type device can be realized. At the same time, using the P+ type diamond epitaxial layer to prepare the ohmic contact is beneficial to reduce the ohmic contact resistance of the device, reduce energy consumption, and optimize the associated RC time constant (resistance-capacitance time constant).

[0027] 2. The present application adjusts the threshold voltage through the back electrode to complete the transition of the device from depletion type to enhancement type. Since the transition of the device type is realized by the back electrode depletion channel, the metal and gate dielectric of the device can be freely selected from different categories. The device can select the metal and gate dielectric according to the user's needs. The device preparation is flexible and can reduce the device preparation cost and improve the device performance.

[0028] 3. The preparation method of the present application has the advantages of simple steps, low cost and strong controllability, and can be suitable for industrialized mass production. The prepared diamond field effect transistor has the advantages of high thermal conductivity, high radiation resistance, flexible selectivity of depletion type and enhancement type, etc. The present application can adjust the depletion degree of the channel by applying different bias to the back electrode, so that the device can be freely adjusted between depletion type and enhancement type, and can flexibly adapt to various use conditions. If a small gate length is used, it has great potential in the field of high power and high frequency.

[0029] The present application will be further described in detail below with reference to the accompanying drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1is a structure schematic diagram of a diamond variable threshold field effect transistor with adjustable channel width provided by an embodiment of the present application;

[0031] Figure 2 is a top view of a diamond variable threshold field effect transistor with adjustable channel width provided by an embodiment of the present application;

[0032] Figure 3 is a flow chart of a preparation method of a diamond variable threshold field effect transistor with adjustable channel width provided by an embodiment of the present application;

[0033] Figures 4a to 4i is a preparation process schematic diagram of a diamond variable threshold field effect transistor with adjustable channel width provided by an embodiment of the present application.

[0034] Legend of reference signs:

[0035] 1-N-type diamond substrate; 2-P-type diamond epitaxial layer; 3-P+type diamond epitaxial layer; 4-source electrode; 5-drain electrode; 6-gate dielectric layer; 7-gate electrode; 8-back electrode. DETAILED DESCRIPTION

[0036] In order to further illustrate the technical means and effects taken by the present application to achieve the predetermined purposes, the following will be described in detail in combination with the drawings and specific embodiments, and a diamond variable threshold field effect transistor with adjustable channel width and a preparation method according to the present application will be described in detail.

[0037] The foregoing and other technical contents, features and effects of the present application can be clearly presented in the following detailed description of specific embodiments in combination with the drawings. Through the description of specific embodiments, the technical means and effects taken by the present application to achieve the predetermined purposes can be understood more deeply and specifically. However, the attached drawings are provided for reference and illustration only, and are not intended to limit the technical solutions of the present application.

[0038] It should be noted that in this document, relational terms such as first and second are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any such actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof are intended to cover non-exclusive inclusions, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by an occurrence of "comprising" does not exclude the presence of additional identical elements in the process, method, article, or apparatus including the element.

[0039] Embodiment one

[0040] Please refer to Figure 1 and Figure 2 , Figure 1 is a structure diagram of a diamond variable threshold field effect transistor with adjustable channel width provided by an embodiment of the present application; Figure 2 is a top view of a diamond variable threshold field effect transistor with adjustable channel width provided by an embodiment of the present application. The diamond variable threshold field effect transistor comprises an N-type diamond substrate 1, a P-type diamond epitaxial layer 2, a P+ type diamond epitaxial layer 3, a source electrode 4, a drain electrode 5, a gate dielectric layer 6, a gate electrode 7 and a back electrode 8, wherein the P-type diamond epitaxial layer 2 is arranged on the upper surface of the N-type diamond substrate 1; the P+ type diamond epitaxial layer 3 is arranged on the upper surface of the P-type diamond epitaxial layer 2 on both sides respectively, and the source electrode 4 and the drain electrode 5 are arranged on the P+ type diamond epitaxial layer 3 on both sides respectively, and the P+ type diamond epitaxial layer 3 forms ohmic contact with the source electrode 4 and the drain electrode 5 above it respectively; the gate dielectric layer 6 is arranged on the upper surface of the P-type diamond epitaxial layer 2 which is not covered by the P+ type diamond epitaxial layer 3, and the gate electrode 7 is arranged on the upper surface of the gate dielectric layer 6 and located between the source electrode 4 and the drain electrode 5; and the back electrode 8 is arranged on the lower surface of the N-type diamond substrate 1.

[0041] In the embodiment, the doping element of the N-type diamond substrate 1 is boron (B), and the doping elements of the P-type diamond epitaxial layer 2 and the P+ type diamond epitaxial layer 3 are both phosphorus (P). The doping concentration of the P-type diamond epitaxial layer 2 is 1×10 15 ~1×10 16 cm -3 ; the doping concentration of the P+ type diamond epitaxial layer 3 is 1×10 19 ~1×10 21 cm -3 . The N-type diamond substrate 1 is selected from single crystal or polycrystalline diamond substrate.

[0042] Further, the thickness of the N-type diamond substrate 1 is 200~300μm, and the thickness of the P-type diamond epitaxial layer 2 and the P+ type diamond epitaxial layer 3 is both 1~5μm.

[0043] Further, the source electrode 4 and the drain electrode 5 both adopt Au material, and the thickness is 50~100nm. The spacing between the source electrode 4 and the drain electrode 5 is 2~10μm.

[0044] The gate electrode 7 adopts Al\Au laminated metal, wherein the Al metal layer is below the Au metal layer, the thickness of the Al metal layer is 10~20nm, and the thickness of the Au metal layer is 40~100nm. Preferably, the thickness of the Al metal layer is 20nm, and the thickness of the Au metal layer is 60nm.

[0045] The back electrode 8 is an Au\Ti laminated metal, wherein the Au metal layer is below the Ti metal layer, the thickness of the Au metal layer is 40-100 nm, and the thickness of the Ti metal layer is 10-20 nm. Preferably, the thickness of the Au metal layer is 80 nm, and the thickness of the Ti metal layer is 20 nm. The gate dielectric layer 6 is deposited by using an ALD (atomic layer deposition) device, and the thickness is 10-20 nm. The width of the gate electrode 7 is 100 μm, and the length of the gate electrode 7 is 4 μm.

[0046] It should be noted that, since the enhancement mode device is realized by regulating the channel by the back electrode bias, the gate dielectric layer is not limited in type, and can be freely deposited according to the requirements of the device. Al\Au is used as the gate electrode metal, Al is easily oxidized to form Al2O3 near the gate dielectric layer, which helps to better reduce the leakage of the device, and since the enhancement mode device is realized by the back electrode, the metal used is not limited in type, and can be freely used according to the requirements of the device, thereby reducing the process cost; through the adjustment of the back electrode voltage bias, the device can be switched between the depletion mode and the enhancement mode, which helps to cope with more application scenarios, and has higher flexibility and potential.

[0047] In this embodiment, the P-type diamond epitaxial layer and the P+ type diamond epitaxial layer are grown on the n-type doped diamond substrate, the P-type diamond epitaxial layer is used as the device channel, the P+ type diamond epitaxial layer forms the ohmic contact of the device, the back electrode is made below the n-type substrate, and the channel width is regulated by regulating the n-p-Schottky barrier height, so as to realize the diamond field effect transistor with adjustable threshold voltage, and the transition from the depletion mode to the enhancement mode device can be realized; at the same time, the use of the P+ type diamond epitaxial layer to prepare the ohmic contact is beneficial to reduce the ohmic contact resistance of the device, reduce the energy consumption, and optimize the associated RC time constant.

[0048] In this embodiment, the threshold voltage is regulated by the back electrode, and the transition from the depletion mode to the enhancement mode device is completed. Since the transition of the device type is realized by the back electrode depletion channel, the metal and the gate dielectric of the device can be freely selected in different categories, the metal and the gate dielectric of the device can be selected according to the requirements of the user, the device preparation is flexible and can reduce the device preparation cost, and the device performance is improved.

[0049] Embodiment two

[0050] On the basis of embodiment one, this embodiment provides a preparation method of the diamond variable threshold field effect transistor with adjustable channel width, which is used for preparing the diamond variable threshold field effect transistor with adjustable channel width as described in embodiment one, such as Figure 3 As shown in FIG. 4, the preparation method comprises the following steps:

[0051] S1: obtaining an N-type diamond substrate 1.

[0052] Specifically, the N-type doped diamond substrate is grown on the N-type diamond substrate 1 by a MPCVD (microwave plasma chemical vapor deposition) device, as shown in FIG. 1. Figure 4a

[0053] S2: sequentially growing a P-type diamond epitaxial layer 2 and a P+ type diamond epitaxial layer 3 on the surface of the N-type diamond substrate 1.

[0054] Specifically, the P-type diamond epitaxial layer 2 and the P+ type diamond epitaxial layer 3 are sequentially grown on the surface of the N-type diamond substrate 1 by a MPCVD device, as shown in FIG. 2. Figure 4b and 4c In this embodiment, the doping element of the N-type diamond substrate 1 is boron (B), and the doping elements of the P-type diamond epitaxial layer 2 and the P+ type diamond epitaxial layer 3 are both phosphorus (P). The doping concentration of the P-type diamond epitaxial layer 2 is 1 x 1015~1 x 1016cm-3; and the doping concentration of the P+ type diamond epitaxial layer 3 is 1 x 1018~1 x 1019cm-3. 15 16 -2 19 21 -2 The N-type diamond substrate 1 is a single crystal or polycrystalline diamond substrate selected.

[0055] S3: etching the P+ type diamond epitaxial layer 3 so that only the P+ type diamond epitaxial layer of the source region and the drain region is reserved, as shown in FIG. 3. Figure 4d

[0056] S4: depositing a source electrode 4 and a drain electrode 5 on the P+ type diamond epitaxial layer 3 of the source region and the drain region, respectively.

[0057] Specifically, 50~100 nm Au metal is deposited as the source-drain electrode by using an electron beam deposition device, as shown in FIG. 4; photoresist is spin-coated, and after exposure and development, the photoresist is reserved in the source-drain electrode region, KI\I2 solution is used to etch the Au metal in the non-electrode region, and only the metal above the P+ type diamond epitaxial layer 3 is reserved, so as to form the source electrode 4 and the drain electrode 5, as shown in FIG. 5. Figure 4e Figure 4f

[0058] S5: depositing a gate dielectric layer 6 on the P-type diamond epitaxial layer 2. In this embodiment, the gate dielectric layer 6 with a thickness of 10~20 nm is grown by using an ALD device, as shown in FIG. 6. Figure 4g

[0059] S6: depositing a gate electrode 7 above the gate dielectric layer 6, so that the gate electrode 7 is located between the source electrode 4 and the drain electrode 5.

[0060] ​​​​​​​​​​Specifically, photoresist is first coated on the upper surface of the device, and the place where metal is to be deposited is exposed and developed, so that the area where metal is to be deposited is free of photoresist. 20\60nm Al\Au metal is deposited as the gate metal of the device, and then acetone solution is used for soaking. The photoresist is washed away by acetone, and the metal on the photoresist is peeled off, completing the preparation of the gate electrode, as shown in Figure 4h Preferably, the photoresist used in the preparation process is AZ6112 or AZ6130.

[0061] In this embodiment, the gate electrode 7 adopts Al\Au laminated metal, wherein the Al metal layer is below the Au metal layer, the thickness of the Al metal layer is 20nm, and the thickness of the Au metal layer is 60nm. The width of the gate electrode 7 is 100μm, and the length of the gate electrode 7 is 4μm.

[0062] S7: Depositing a back electrode 8 on the lower surface of the N-type diamond substrate 1.

[0063] Specifically, 20\80nm Ti\Au metal is deposited on the lower surface of the N-type diamond substrate 1 as the back electrode 8 using an electron beam deposition device, completing the preparation of the device, as shown in Figure 4i That is, the back electrode 8 adopts Au\Ti laminated metal, wherein the Au metal layer is below the Ti metal layer, the thickness of the Au metal layer is 80nm, and the thickness of the Ti metal layer is 20nm.

[0064] The preparation method of this embodiment has the advantages of simple steps, low cost, and strong controllability, and can be suitable for industrial large-scale production. The prepared diamond field effect tube has the advantages of high thermal conductivity, high radiation resistance, flexible selectivity of depletion type and enhancement type, etc. By applying different bias to the back electrode, the depletion degree of the channel can be adjusted, so that the device can be freely adjusted between depletion type and enhancement type, and can flexibly adapt to various use conditions. If a small gate length is used, it has great potential in the field of high power and high frequency.

[0065] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, some simple deductions or substitutions can be made without departing from the concept of the present application, and all of them should be regarded as falling within the protection scope of the present application.

Claims

1. A diamond variable threshold field effect transistor of adjustable channel width, characterized by, It comprises an N-type diamond substrate (1), a P-type diamond epitaxial layer (2), a P+ type diamond epitaxial layer (3), a source electrode (4), a drain electrode (5), a gate dielectric layer (6), a gate electrode (7) and a back electrode (8), wherein, The P-type diamond epitaxial layer (2) is arranged on the upper surface of the N-type diamond substrate (1); the P+ type diamond epitaxial layer (3) is arranged on the upper surface of the P-type diamond epitaxial layer (2) on both sides respectively; the source electrode (4) and the drain electrode (5) are arranged on the P+ type diamond epitaxial layer (3) on both sides respectively; the P+ type diamond epitaxial layer (3) forms ohmic contact with the source electrode (4) and the drain electrode (5) above it respectively; The gate dielectric layer (6) is arranged on the upper surface of the P-type diamond epitaxial layer (2) which is not covered by the P+ type diamond epitaxial layer (3); the gate electrode (7) is arranged on the upper surface of the gate dielectric layer (6) and located between the source electrode (4) and the drain electrode (5); The back electrode (8) is arranged on the lower surface of the N-type diamond substrate (1); The gate electrode (7) adopts Al\Au laminated metal, wherein the Al metal layer is below the Au metal layer, the thickness of the Al metal layer is 10-20 nm, and the thickness of the Au metal layer is 40-100 nm; The back electrode (8) adopts Au\Ti laminated metal, wherein the Au metal layer is below the Ti metal layer, the thickness of the Au metal layer is 40-100 nm, and the thickness of the Ti metal layer is 10-20 nm; The threshold voltage adjustable diamond field effect transistor is realized by adjusting the n-p-Schottky barrier height to control the channel width, realizing the transition from depletion type to enhancement type device; at the same time, the P+ type diamond epitaxial layer is used to prepare ohmic contact to reduce the ohmic contact resistance of the device, reduce energy consumption and optimize the associated RC time constant.

2. The tunable channel width diamond variable threshold field effect transistor of claim 1, wherein, The doping concentration of the P-type diamond epitaxial layer (2) is 1×10⁻⁶. 15 ~1×10 16 cm -3 The doping concentration of the P+ type diamond epitaxial layer (3) is 1×10⁻⁶. 19 ~1×10 21 cm -3 .

3. The tunable channel width diamond variable threshold field effect transistor of claim 2, wherein, The doping element of the N-type diamond substrate (1) is boron, and the doping elements of the P-type diamond epitaxial layer (2) and the P+ type diamond epitaxial layer (3) are phosphorus.

4. The tunable channel width diamond variable threshold field effect transistor of claim 1, wherein, The thickness of the N-type diamond substrate (1) is 200-300 µm, and the thickness of the P-type diamond epitaxial layer (2) and the P+ type diamond epitaxial layer (3) is 1-5 µm.

5. The tunable channel width diamond variable threshold field effect transistor of claim 1, wherein, The source electrode (4) and the drain electrode (5) both adopt Au material with a thickness of 50-100 nm.

6. The tunable channel width diamond variable threshold field effect transistor of claim 1, wherein, The spacing between the source electrode (4) and the drain electrode (5) is 2-10 µm.

7. A method of fabricating a diamond variable threshold field effect transistor with tunable channel width, characterized in that, The preparation method of the adjustable channel width diamond variable threshold field effect transistor of any one of claims 1-6 comprises: S1: obtaining an N-type diamond substrate; S2: growing a P-type diamond epitaxial layer and a P+ type diamond epitaxial layer on the upper surface of the N-type diamond substrate in sequence; S3: etching the P+ type diamond epitaxial layer so that only the P+ type diamond epitaxial layer of the source region and the drain region is reserved; S4: depositing a source electrode and a drain electrode on the P+ type diamond epitaxial layer of the source region and the drain region respectively; S5: depositing a gate dielectric layer on the P-type diamond epitaxial layer; S6: depositing a gate electrode over the gate dielectric layer, such that the gate electrode is located between the source electrode and the drain electrode; S7: depositing a back electrode on the lower surface of the N-type diamond substrate.

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