A strong polarization heterojunction Fin-HEMT device and preparation method

Abstract

The present invention relates to a strong polarization heterojunction Fin-HEMT device. The strong polarization heterojunction Fin-HEMT device includes a channel layer, which is an unintentionally doped ε-Ga2O3 layer. A groove is etched on the upper surface of the channel layer along the gate width direction to form a Fin structure, wherein the etching depth is h; an insertion layer: the band gap width of the insertion layer material is smaller than the band gap width of ε-Ga2O3, the insertion layer is deposited on the channel layer and its thickness in the groove is d1; a barrier layer, which is deposited on the insertion layer and its thickness in the groove is d2, and the barrier layer is ε-(Al x Ga 1‑x )2O3 layer, with d1+d2<h; a gate electrode formed on the barrier layer and having a fin structure; and source and drain electrodes disposed on either side of the gate electrode, each in contact with the channel layer, the insertion layer, and the barrier layer. This device exhibits excellent multi-threshold coupling and improves device linearity without sacrificing channel width and two-dimensional electron gas concentration between the fins.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a strongly polarized heterojunction Fin-HEMT device and a preparation method thereof. Background Art

[0002] ε-phase Ga2O3 is a polar phase of the hexagonal system, which has a strong spontaneous polarization (spontaneous polarization charge up to 2e 14 cm -2 , one order of magnitude higher than GaN), so when forming with aluminum gallium oxide (Al x Ga 1-x )2O3 / Ga2O3 heterojunction, there is no need for δ-modulation doping. High-concentration 2DEG can be generated by spontaneous polarization and piezoelectric polarization alone. The concentration can be adjusted by changing the Al component. The confinement and mobility of the polarization channel have obvious advantages over the δ-modulation doped channel.

[0003] In high-voltage and strong-irradiation working environments, GaAs limits the device's voltage-withstand and radiation-resistance capabilities due to its narrow bandgap and low critical breakdown field strength; GaN has a large density of epitaxial defects on heterogeneous substrates and a large number of defect energy levels in the bandgap, which not only causes current collapse, but also affects the device's voltage-withstand and radiation-resistance characteristics. The ε-Ga2O3 polarized heterojunction significantly increases the 2DEG concentration and significantly improves the channel mobility, combined with its ultra-wide bandgap and high critical breakdown field strength, making it have great application potential in the high-voltage and radiation-resistance high-frequency field. The above characteristics make ε-(Al x Ga 1-x )2O3 / Ga2O3 strong polarization heterojunction has great application potential in the field of high voltage and high frequency. Based on this, ε-(Al x Ga 1-x )2O3 / Ga2O3 strong polarization barrier heterojunction HEME structure. Summary of the Invention

[0004] Based on the above description, the present invention provides a strongly polarized heterojunction Fin-HEMT device, which has a good multi-threshold coupling effect and can improve the linearity of the device without sacrificing the channel width and two-dimensional electron gas concentration between the Fins.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: The present invention provides a strong polarization heterojunction Fin-HEMT device, comprising at least

[0006] A channel layer, wherein the channel layer is an unintentionally doped ε-Ga2O3 layer, and a groove is etched on the upper surface of the channel layer along the gate width direction to form a Fin structure, wherein the etching depth is h;

[0007] Insertion layer: the band gap width of the insertion layer material is smaller than the band gap width of ε-Ga2O3, and the insertion layer is deposited on the channel layer and its thickness in the trench is d1;

[0008] The barrier layer is deposited on the insertion layer and has a thickness of d2 in the trench. The barrier layer is ε-(Al x Ga 1-x )2O3 layer, and d1+d2<h;

[0009] a gate electrode, wherein the gate electrode is formed on the barrier layer and has a fin structure;

[0010] The invention also includes a source electrode and a drain electrode arranged on both sides of the gate electrode, wherein the source electrode and the drain electrode are both in contact with the channel layer, the insertion layer and the barrier layer.

[0011] As a preferred embodiment, the device further includes

[0012] a substrate having opposing first and second surfaces;

[0013] A buffer layer is deposited on the first surface of the substrate, and the channel layer is formed on the buffer layer.

[0014] Specifically, the substrate includes but is not limited to SiC, GaN, and Ga2O3 substrates; the buffer layer includes but is not limited to Fe-doped gallium oxide structure; the material of the insertion layer includes but is not limited to GaN and InGaN; the barrier layer is N-type doped ε-(Al x Ga 1-x )2O3 layer.

[0015] As a preferred embodiment, the source-drain electrodes are in contact with the channel layer, the insertion layer and the barrier layer through a contact layer.

[0016] The present invention also provides a method for preparing the above-mentioned strong polarization heterojunction Fin-HEMT device, comprising the following steps:

[0017] An unintentionally doped ε-Ga2O3 layer is epitaxially grown on a substrate as a channel layer, a mask is made on the channel layer, and then array trenches are etched along the gate width direction in the active area;

[0018] Removing the mask and sequentially epitaxially growing the insertion layer and the barrier layer, and ensuring that the sum of the thickness of the insertion layer and the barrier layer in the trench is less than the depth of the etched trench;

[0019] A mask is made on the barrier layer and the source and drain regions are etched to make source and drain electrodes. The mask is removed and an electron beam lithography machine is used to perform gate electrode lithography to make a gate electrode.

[0020] As a preferred embodiment, the step of growing a contact layer in the source and drain regions is further included before the source and drain electrodes are fabricated. After the contact layer is fabricated, the source and drain electrodes are fabricated on the contact layer.

[0021] Furthermore, the contact layer is produced by selective etching and regrowth using a hard mask. Specifically, a hard mask is used for dry etching, the etching is terminated in the channel layer structure, and then a heavily doped N-type gallium oxide contact layer is grown, and then metal is deposited on the contact layer.

[0022] Furthermore, the contact layer is etched using a soft mask. Specifically, a soft mask is used, the resist is washed after etching, and then a heavily doped N-type gallium oxide layer is regrown on the entire wafer. The gallium oxide between the source and drain is removed by etching, and then metal is deposited on the remaining gallium oxide.

[0023] As a preferred embodiment, a buffer layer is first epitaxially grown on the substrate before the channel layer is epitaxially grown.

[0024] The present invention etches a groove on the channel layer, deposits an insertion layer and a barrier layer, and ensures that the total thickness of the insertion layer and the barrier layer in the groove is less than the etched groove height, and then makes a gate electrode. Through the epitaxy of the barrier layer, the 2DEG in the Fin structure and between the Fin-Fin are allowed to exist, realizing the coupling of the side gate and the top gate without losing the channel width; at the same time, a specific channel insertion layer is introduced to form (Al x Ga 1-x )2O3 / insertion channel layer / Ga2O3 heterojunction forms a quantum well to increase the 2DEG channel carrier concentration and confinement, further improving the channel mobility of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the three-dimensional structure of a strongly polarized heterojunction Fin-HEMT device provided in an embodiment of the present invention;

[0026] Figure 2 for Figure 1 Schematic diagram of the gate position of the strongly polarized heterojunction Fin-HEMT device shown in;

[0027] Figure 3 for Figure 1 The process flow chart of the preparation of the strong polarization heterojunction Fin-HEMT device is shown in FIG.

[0028] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0029] 1 substrate, 2 buffer layer, 3 channel layer, 4 insertion layer, 5 barrier layer, 6 source electrode, 7 drain electrode, 8 gate electrode. DETAILED DESCRIPTION

[0030] To facilitate understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings. The accompanying drawings provide embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to make the disclosure of the present application more thorough and comprehensive.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0032] It should be noted that the figures and embodiments described in this application are illustrative rather than restrictive. Identical figures throughout the embodiments identify identical structures. Furthermore, for ease of understanding and description, the figures may exaggerate the thickness of certain layers, films, panels, and regions. Furthermore, the term "on" refers to positioning an element above or below another element, but does not inherently mean positioning an element on the upper side of another element based on gravity.

[0033] like Figure 1 、 2 As shown, a strong polarization heterojunction Fin-HEMT device at least includes

[0034] Channel layer 3, which is an unintentionally doped ε-Ga2O3 layer. A groove is etched on the upper surface of the channel layer 3 along the gate width direction to form a Fin structure, where the etching depth is defined as h;

[0035] Insertion layer 4, the band gap width of the material of insertion layer 4 is smaller than the band gap width of ε-Ga2O3, insertion layer 4 is deposited on channel layer 3 and its thickness in the trench is d1;

[0036] The barrier layer 5 is deposited on the insertion layer 4 and has a thickness of d2 in the trench. The barrier layer is ε-(Al x Ga 1-x )2O3 layer, and satisfy d1+d2<h;

[0037] A gate electrode 8 is formed on the barrier layer and has a fin structure;

[0038] The device further includes a drain electrode 6 and a source electrode 7 disposed on both sides of the gate electrode. Both the source electrode 7 and the drain electrode 6 are in contact with the channel layer 3 , the insertion layer 4 and the barrier layer 5 .

[0039] In the prior art, the channel layer and barrier layer are usually etched together after deposition to form a Fin structure, and then the gate electrode is made. However, in the present application, the channel layer 3 is first etched, and then the insertion layer 4 and the barrier layer 5 are deposited in sequence, and the thickness of the insertion layer and the barrier layer in the trench is ensured to be less than the depth of the trench etching, so that 2DEG can be generated on the channel layer side of the horizontal heterojunction and sidewall heterojunction in the Fin structure and the horizontal heterojunction interface between Fin-Fin, so that the channel width and two-dimensional electron gas concentration between Fins are not lost, and the barrier layer on the sidewall is relatively thinner than the plane, so that the horizontal channel in the Fin structure is jointly controlled by the top gate and the side gate. The sidewall channel in the Fin structure is mainly controlled by the side gate, and the channel between Fin-Fin is mainly controlled by the bottom gate, further enhancing the multi-threshold coupling effect and improving the linearity of the device.

[0040] In the present invention, the channel layer, the insertion layer and the barrier layer are sequentially deposited to form (Al x Ga 1-x )2O3 / insertion channel layer / Ga2O3 heterojunction. For the heterojunction channel, 2DEG is generated on one side of the insertion channel layer at the heterojunction interface by polarization, thereby improving the channel mobility and reducing the on-resistance. At the same time, it also ensures that each channel 2DEG is connected to the source and drain regrowth area, which helps to form a good ohmic contact and simplifies the annealing process.

[0041] On the basis of the above, the strong polarization heterojunction Fin-HEMT device provided by the present invention further includes a substrate 1, the substrate 1 having a first surface and a second surface opposite to each other;

[0042] The buffer layer 2 is deposited on the first surface of the substrate 1 , and the channel layer 3 is formed on the buffer layer 2 .

[0043] It can be understood that the substrate 1 includes but is not limited to SiC, GaN, and Ga2O3 substrates, the buffer layer 2 includes but is not limited to Fe-doped GaN structure, and the material of the insertion layer includes but is not limited to GaN and InGaN.

[0044] Furthermore, the barrier layer 5 is N-type doped ε-(Al x Ga 1-x )2O3 layer, the 2DEG concentration inserted into the channel layer can be further increased by appropriately N-type doping the barrier layer.

[0045] The present invention also provides a method for preparing the above-mentioned strong polarization heterojunction Fin-HEMT device, comprising the following steps:

[0046] An unintentionally doped ε-Ga2O3 layer is epitaxially grown on the substrate 1 as the channel layer 3, a mask is made on the channel layer 3, and then array trenches are etched along the gate width direction in the active area;

[0047] Remove the mask and sequentially grow the insertion layer 4 and the barrier layer 5 epitaxially, and ensure that the sum of the thickness of the insertion layer 4 and the barrier layer 5 in the trench is less than the depth of the etched trench;

[0048] A mask is made on the barrier layer 5 and the source and drain regions are etched to form source and drain electrodes. The mask is removed and an electron beam lithography machine is used to perform gate electrode lithography to form a gate electrode.

[0049] It is understandable that the buffer layer 2 may be epitaxially grown on the substrate 1 before the channel layer 3 is epitaxially grown.

[0050] In the present invention, the source and drain electrodes contact the trench layer, the insertion layer, and the barrier layer through the gallium oxide contact layer. This method can simplify the annealing process and effectively reduce the ohmic contact resistance, thereby further helping to improve the frequency and power characteristics of the device.

[0051] Furthermore, the contact layer can be manufactured by selective etching and regrowth using a hard mask or by etching using a soft mask.

[0052] Among them, the method of using hard mask selective etching and regrowth is: using a hard mask, through dry etching, the etching is terminated in the channel layer structure, and then a heavily doped N-type gallium oxide contact layer is grown, and then metal is deposited on the contact layer to make source and drain electrodes.

[0053] The soft mask method is: use a soft mask, wash the resin after etching, and then re-grow a heavily doped N-type gallium oxide layer on the entire wafer. Remove the gallium oxide between the source and drain by etching, and then deposit metal on the remaining gallium oxide to make source and drain electrodes.

[0054] In addition, after the regrowth etching is completed, the source and drain electrodes can also omit the secondary epitaxy and directly deposit ohmic metal so that the 2DEG is directly in contact with the sidewall metal, and then annealing is performed to form a groove metal ohmic electrode.

[0055] The following is a detailed explanation using a specific case. Figure 3 A method for preparing a strongly polarized heterojunction Fin-HEMT device comprises the following steps:

[0056] Step 1: Epitaxial substrate preparation: The substrate can be selected from various high-resistance substrates, including but not limited to SiC, GaN, and Ga2O3. This solution uses SiC as an example. The buffer and channel layers are then grown using MOCVD (metal-organic chemical vapor deposition) or MBE (molecular beam epitaxy). The buffer layer can be made of Fe-doped gallium oxide with a thickness of T1, while the channel layer is made of unintentionally doped ε-Ga2O3 with a thickness of T2.

[0057] Step 2: Deposition and etching of the active area barrier regrowth mask: To prepare a Fin structure with side-gate and top-gate coupling control, a selective etching is performed along the gate width direction in the active area using a certain duty cycle. The etching depth T3 (preferably 20-200nm) is greater than the thickness of the subsequent epitaxial insertion layer and barrier layer to ensure that the Fin structure has side-gate control. The mask can use photoresist as a soft mask to simplify the process steps, or a hard mask (including but not limited to various dielectric layers and metal masks: SiO2, SiN, Ni, etc.) can be used to improve the etching morphology and reduce process risks. Here, a SiO2 mask layer with a thickness of T4 is deposited as an example. After photolithography stripping, the soft mask pattern is transferred to the hard mask. Subsequently, dry etching is performed using a Cl-based plasma. The etching is terminated in the channel layer structure to ensure that the deposited barrier layer is still epitaxially grown on the basis of the channel layer.

[0058] Step 3: Mask removal and regrowth of active area insertion layer and barrier layer: After etching, the mask layer is removed, and then the insertion layer and the unintentionally doped ε-(Al2O3) with a thickness of T5 are deposited in the active area using MBE. x Ga 1-x )2O3 layer as a barrier layer, forming Al x Ga 1-x )2O3 / insertion channel layer / Ga2O3 heterojunction structure, due to the ε-(Al x Ga 1-x )2O3 itself has polarity and can generate 2DEG on one side of the ε-Ga2O3 channel layer in the Fin structure and between the Fin-Fin structure.

[0059] Step 4: Deposition and etching of mask for regrowth of source and drain regions: In order to ensure good contact between the channel and the source and drain electrodes, the source and drain electrodes are made by selective etching and regrowth. x Ga 1-x )2O3 has a relatively large etching selectivity compared to photoresist in Cl-based ICP etching. If high power is used for a long time, there is a risk of glue formation. Soft masks are difficult to meet etching requirements. Therefore, a hard mask is used (including but not limited to various dielectric layers and metal masks: SiO2, SiN, Ni, etc.). Here, a SiO2 mask layer with a thickness of T6 deposited by sputtering is used as an example. After photolithographic stripping, the soft mask pattern is transferred to the hard mask. Subsequently, dry etching is performed using a Cl-based plasma. The etching is terminated in the channel layer structure, below the two-dimensional electron gas, to ensure that the highly doped regrowth can contact the 2DEG of the heterojunction channel.

[0060] Step 5: Regrowth of source and drain regions and removal of the hard mask: MBE is then used to regrow the source and drain etched regions to grow a heavily doped N-type gallium oxide contact layer, and then BOE solution is used to remove the SiO2 mask.

[0061] Step 6: Fabrication of source and drain ohmic electrodes (schematic cross-section of source and drain electrode locations): After secondary epitaxy, source and drain metal electrodes are deposited using electron beam evaporation or magnetron sputtering. Ti / Al / Ni / Au are commonly used metal systems. If the regrowth doping concentration is not high enough to directly form a good ohmic contact, annealing can be performed to improve the contact. The annealing temperature can be 400-600°C, the annealing atmosphere can be nitrogen, and the annealing time can be 30 seconds to 1 minute. Isolation between active areas is then performed, which can be achieved by implantation or MESA etching.

[0062] Step 7: Fin-structure gate electrode fabrication: Electron beam lithography is performed using an electron beam lithography machine, using a PMMA-based electron photoresist. Three coats are applied. The sensitivity and resolution of the photoresist are adjusted by varying the baking temperature. The exposure area and exposure dose are then adjusted appropriately, so that after a single exposure and development, the composite photoresist layer forms a T-shaped gate electrode lithographic topography (the T-shaped gate cap is not shown in the schematic diagram). Gate metal is then deposited using electron beam evaporation or magnetron sputtering. The metal system can be, but is not limited to, a Ni / Au combination. Because the sidewall barrier layer is relatively thin compared to the planar surface, the horizontal channel in the fin structure is controlled by both the top gate and the side gate. The sidewall channel in the fin structure is primarily controlled by the side gate, while the channel between the fins is primarily controlled by the top gate. This improves linearity through multi-threshold coupling while increasing the device conduction capability by increasing the actual gate width. After gate electrode deposition, the stripping step is performed, completing the key process steps of device fabrication.

[0063] The above device structure has at least the following beneficial technical effects:

[0064] (1) High conduction capability: no loss of channel width and two-dimensional electron gas concentration between fins;

[0065] (2) High linearity: The horizontal channel in the Fin structure realizes the joint control of the top gate and the side gate. The Fin sidewall channel is mainly controlled by the side gate, and the horizontal channel between the Fin and the Fin is mainly controlled by the bottom gate, thereby further enhancing the multi-threshold coupling effect and improving the linearity of the device;

[0066] (3) Strong polarization: ε phase (Al x Ga 1-x )2O3 / GaN / Ga2O3 heterojunction has a strong polarization, which can produce a high concentration of 2DEG on the channel layer side of the heterojunction interface;

[0067] (4) High withstand voltage: ε-Ga2O3 has a bandgap of ~5eV and a critical breakdown field strength of ~8MV / cm, which effectively improves the withstand voltage characteristics of the device;

[0068] (5) High mobility: Alx Ga 1-x )2O3 / insertion channel layer / Ga2O3 heterojunction channel can effectively improve the confinement and mobility of channel carriers. In addition, the channel mobility can be further improved through the Fin structure;

[0069] (6) High output power: High on-state current, combined with the high critical breakdown field strength of the material, enables the device to be used in high-voltage and high-current working scenarios, generating high output power;

[0070] (7) Low contact resistance: By regrowth of the source and drain regions, the channel 2DEG is ensured to be connected to the source and drain regions, which helps to form a good ohmic contact and simplifies the annealing process.

[0071] (8) Low side gate leakage: Compared with conventional Fin HEMT, the side gate is not in direct contact with the two-dimensional electron gas, but is in contact with the barrier layer similar to the top gate, which can effectively reduce the side gate leakage.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A strongly polarized heterojunction Fin-HEMT device, characterized in that: At least include A channel layer, wherein the channel layer is an unintentionally doped ε-Ga2O3 layer, and a groove is etched on the upper surface of the channel layer along the gate width direction to form a Fin structure, wherein the etching depth is h; Insertion layer: the band gap width of the insertion layer material is smaller than the band gap width of ε-Ga2O3, the insertion layer is deposited on the channel layer and its thickness in the trench is d1; A barrier layer, wherein the barrier layer is deposited on the insertion layer and has a thickness d2 in the trench, the barrier layer is an ε-(AlxGa1-x)2O3 layer, and d1+d2<h; a gate electrode, wherein the gate electrode is formed on the barrier layer and has a fin structure; Also included is a source electrode and a drain electrode disposed on both sides of the gate electrode, wherein the source electrode and the drain electrode are in contact with the channel layer, the insertion layer and the barrier layer; The source and drain electrodes are in contact with the channel layer, the insertion layer and the barrier layer through the contact layer; the barrier layer is N-type doped ε-(Al x Ga 1-x )2O3 layer.

2. The strong polarization heterojunction Fin-HEMT device according to claim 1, characterized in that: Also includes a substrate having opposing first and second surfaces; A buffer layer is deposited on the first surface of the substrate, and the channel layer is formed on the buffer layer.

3. The strong polarization heterojunction Fin-HEMT device according to claim 2, characterized in that: The substrate includes but is not limited to SiC, GaN, and Ga2O3 substrates; the buffer layer includes but is not limited to Fe-doped ε-gallium oxide structure; the material of the insertion layer includes but is not limited to GaN and InGaN.

4. The method for preparing a strong polarization heterojunction Fin-HEMT device according to any one of claims 1 to 3, characterized in that: The following steps are involved: An unintentionally doped ε-Ga2O3 layer is epitaxially grown on a substrate as a channel layer, a mask is made on the channel layer, and then array trenches are etched along the gate width direction in the active area; Removing the mask and sequentially epitaxially growing the insertion layer and the barrier layer, and ensuring that the sum of the thickness of the insertion layer and the barrier layer in the trench is less than the depth of the etched trench; A mask is made on the barrier layer and the source and drain regions are etched to make source and drain electrodes. The mask is removed and an electron beam lithography machine is used to perform gate electrode lithography to make a gate electrode.

5. The method for preparing a strong polarization heterojunction Fin-HEMT device according to claim 4, characterized in that: Before the source-drain electrodes are manufactured, a step of growing a contact layer in the source-drain region is also included. After the contact layer is manufactured, the source-drain electrodes are manufactured on the contact layer.

6. The method for preparing a strong polarization heterojunction Fin-HEMT device according to claim 5, characterized in that: The contact layer is manufactured by selective etching and regrowth using a hard mask, specifically, by dry etching using a hard mask, the etching is terminated in the channel layer structure, and then a heavily doped N-type gallium oxide contact layer is grown.

7. The method for preparing a strong polarization heterojunction Fin-HEMT device according to claim 5, characterized in that: The source and drain electrodes are etched using a soft mask. Specifically, a soft mask is used, and after etching, the resist is washed off. Then, a heavily doped N-type gallium oxide layer is regrown on the entire wafer, and the gallium oxide between the source and drain is removed by etching.

8. The method for preparing a strong polarization heterojunction Fin-HEMT device according to claim 4, characterized in that: A buffer layer is firstly epitaxially grown on the substrate before the channel layer is epitaxially grown.

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