CN115966603A - High-linearity HEMT device and preparation method thereof - Google Patents

Abstract

The invention relates to a high-linearity HEMT device and a preparation method thereof, aiming at improving the linearity of the HEMT device and avoiding the non-linear problems of transconductance roll-off caused by the non-linear factors of the device, transconductance peak phenomenon caused by overlarge transconductance derivative change and the like as much as possible from a structure optimization approach. A first aspect of the present invention provides a high linearity HEMT device, comprising: the buffer layer is formed on the substrate, and the nucleation layer, the buffer layer, the barrier layer and the passivation layer are sequentially stacked on the substrate from bottom to top; the passivation layer is provided with a gate groove, the bottom of the gate groove is positioned in the barrier layer, and a gate is arranged in the gate groove; a source electrode and a drain electrode are respectively arranged on two sides of the grid electrode, and are in ohmic contact with the buffer layer; the bottom of the gate trench has the following shape: along the width direction of grid, the bottom of grid groove is unsmooth form, by concave unit and protruding unit interval distribution, and be regular periodic variation distribution.

Description

A kind of highly linear HEMT device and its preparation method

technical field

The invention relates to the field of semiconductor devices, in particular to a highly linear HEMT device and a preparation method thereof.

Background technique

Wide bandgap semiconductor material GaN is an ideal material for preparing microwave power devices. Compared with Si material, GaN material has wide band gap, adjustable band gap (0.7eV-6.2eV), easy to form heterostructure, high temperature resistance, high pressure resistance, corrosion resistance, radiation resistance, high electron peak drift speed, extremely strong Polarization effect, high two-dimensional electron gas concentration and other characteristics. Compared with the second-generation semiconductor material GaAs, its 2DEG concentration without doping is an order of magnitude higher than GaAs, and its power density is also an order of magnitude higher than GaAs, which means that in various power amplifiers In applications, the use of GaN-based devices can save area, reduce power consumption, and save costs.

HEMT is the most widely used device structure in GaN power devices. Compared with MOSFET, GaN HEMT has higher frequency characteristics because of its high electron mobility.

With the sharp increase in the demand for communication and wireless systems, linear and low-noise systems have become potential solutions to achieve higher system performance. The trade-off between efficiency and output power is more difficult, and the realization of related circuit technology becomes more and more complicated. Therefore, innovative designs with higher transconductance and improved linearity are urgently needed.

From the perspective of the device level, when a modulated interference model and a signal to be received enter the device at the same time, due to the nonlinear effect of the device, the interference signal will be transferred to the signal carrier to form cross modulation and intermodulation distortion. When two or more interference signals enter the device at the same time, due to the nonlinear effect of the device, the combined frequency of the interference signals is sometimes just equal to or close to the frequency of the useful signal, resulting in intermodulation distortion. The nonlinear sources of the device are mainly the nonlinearity of the channel resistance, the short channel effect, and the uneven distribution of the electric field in the channel. Therefore, how to improve the linearity is an urgent problem to be solved for HEMT devices.

For this reason, the present invention is proposed.

Contents of the invention

The main purpose of the present invention is to provide a highly linear HEMT device and its preparation method, aiming at improving the linearity of the HEMT device, avoiding the transconductance roll-off caused by the nonlinear factors of the device as far as possible from the way of structural optimization, and Excessive changes in the transconductance derivative cause nonlinear problems such as transconductance spikes.

In order to achieve the above objectives, the present invention provides the following technical solutions.

A first aspect of the present invention provides a highly linear HEMT device, comprising:

a substrate, and a nucleation layer, a buffer layer, a barrier layer and a passivation layer stacked sequentially from bottom to top on the substrate;

Wherein, the passivation layer is provided with a gate groove, the bottom of the gate groove is located in the barrier layer, and a gate is arranged in the gate groove; a source and a drain are respectively arranged on both sides of the gate , both the source and the drain are in ohmic contact with the buffer layer;

The bottom of the gate groove has the following shape: along the width direction of the grid, the bottom of the gate groove is uneven, and the concave and convex units are distributed at intervals, and the distribution is regular and periodically changing.

A second aspect of the present invention provides a method for preparing a highly linear HEMT device, comprising:

provide the substrate;

Stacking on the substrate in sequence to form a nucleation layer, a buffer layer, and a barrier layer;

spin-coating photoresist on the barrier layer;

Etching the photoresist to form a plurality of grooves distributed at intervals, the grooves penetrating through the photoresist;

Performing high-temperature vacuum hot plate reflow treatment on the photoresist formed with the grooves at a temperature of 110-150°C;

performing low-damage etching on the barrier layer, removing the photoresist, and forming gate grooves with uneven bottom;

forming a passivation layer on the barrier layer, the passivation layer not filling the gate groove;

forming a gate in the gate groove;

Source and drain are made on both sides of the gate respectively.

Compared with the prior art, the present invention has achieved the following technical effects:

In the HEMT device provided by the present invention, the bottom of the gate groove has a continuous and gradually changing uneven shape along the gate width direction, which leads to a continuous and gradual change in the distance from the gate bottom to the channel along the gate width direction, making this structure equivalent to many Devices with different gate drive static bias voltages are connected in parallel, and the transconductance derivatives can cancel each other in the linear region, suppress unwanted harmonic factors, suppress the peak behavior of transconductance in this region, and there is always a pair of conducting devices Another pass-through device performs transconductance compensation to cope with the transconductance roll-off near the pinch-off region. This not only enables the HEMT with this structure to obtain a flat transconductance profile with a wide range and good linearity, but also basically does not cause transconductance loss. In addition, the invention reduces the distortion, and at the same time reduces the design complexity and follow-up cost of related pre-distortion circuits.

Description of drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiment. The drawings are only for the purpose of illustrating a preferred embodiment and are not to be considered as limiting the invention.

Fig. 1 is a schematic cross-sectional view of a HEMT device provided by the present invention, and the cross-sectional direction is the gate length direction;

FIG. 2 is a schematic diagram of another cross-sectional direction of the HEMT device shown in FIG. 1, and the cross-sectional direction is the gate width direction;

FIG. 3 is a schematic cross-sectional view of another HEMT device provided by the present invention, and the cross-sectional direction is the gate length direction;

FIG. 4 is a schematic cross-sectional view of another HEMT device provided by the present invention, and the cross-sectional direction is the gate length direction;

5 to 10 are structural diagrams obtained in each step of the HEMT device manufacturing method provided by the present invention.

Detailed ways

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. It should be understood, however, that these descriptions are exemplary only, and are not intended to limit the scope of the present disclosure. Also, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concept of the present disclosure.

Various structural schematic diagrams according to embodiments of the present disclosure are shown in the accompanying drawings. The figures are not drawn to scale, with certain details exaggerated and possibly omitted for clarity of presentation. The shapes of the various regions and layers shown in the figure, as well as their relative sizes and positional relationships are only exemplary, and may deviate due to manufacturing tolerances or technical limitations in practice, and those skilled in the art will Regions/layers with different shapes, sizes, and relative positions can be additionally designed as needed.

In the context of the present disclosure, when a layer/element is referred to as being "on" another layer/element, the layer/element may be directly on the other layer/element, or there may be intervening layers/elements in between. element. Additionally, if a layer/element is "on" another layer/element in one orientation, the layer/element can be located "below" the other layer/element when the orientation is reversed.

In order to solve the nonlinear problem existing in the prior art, the present invention provides a HEMT device with a novel structure, which has the shape shown in Figures 1 and 2, specifically as follows.

Referring to FIGS. 1 and 2 , the highly linear HEMT device includes a substrate, and a nucleation layer, a buffer layer, a barrier layer and a passivation layer stacked sequentially on the substrate from bottom to top. The substrate can be any substrate known by those skilled in the art to carry components of semiconductor integrated circuits, such as silicon-on-insulator (silicon-on-insulator, SOI), bulk silicon (bulk silicon), silicon carbide, germanium, silicon germanium , gallium arsenide or germanium on insulator, etc., the corresponding top layer semiconductor material is silicon, germanium, silicon germanium or gallium arsenide, etc., preferably silicon carbide substrate, silicon carbide substrate can be 4H-SiC, 3C-SiC or 6H- Typical substrates such as SiC. The nucleation layer is preferably AlN material, the buffer layer is preferably GaN material, the barrier layer is preferably AlGaN material, and the passivation layer is preferably SiN material. The chemical formulas of these materials in the HEMT device of the present invention are just abbreviations, and do not mean that each element is in an equimolar ratio combination. Each layer has its conventionally set thickness, for example, the thickness of the nucleation layer is between 50-100 nm, the thickness of the buffer layer is between 1.5-2.5 μm, the thickness of the barrier layer is between 20-30 nm, and the thickness of the passivation layer is The thickness is between 100nm and 150nm. The above dimensions are only typical dimensions listed in the present invention and do not limit the application of the present invention. The dimensions can be adjusted randomly during practical application.

Among them, the passivation layer of the HEMT device is provided with a gate groove, the bottom of the gate groove of the HEMT device is located in the barrier layer of the HEMT device, and a gate is arranged in the gate groove of the HEMT device; a source and a drain are respectively provided on both sides of the gate of the HEMT device , both the source and the drain are in ohmic contact with the buffer layer of the HEMT device. Usually, the gate is closer to the source than the drain. For example, when the distance between the source and the drain is 2.4-4 μm, the distance between the gate and the source is 0.8-1.0 μm, and the distance between the gate and the drain is 1.6-4 μm. 3.0 μm, the grid width ranges from 25 to 200 μm, and the grid length ranges from 0.1 to 0.2 μm. The above dimensions are only typical dimensions listed in the present invention, and do not limit the application of the present invention. The dimensions can be adjusted randomly in the actual application process . Any metal material with good conductivity and stability can be selected for the source, drain and gate, such as common titanium, tungsten, aluminum, etc.

The most critical improvement of the present invention is that there is a special requirement for the shape of the gate groove. Specifically, the bottom of the gate groove has the following shape: along the width direction of the gate of the HEMT device, the bottom of the gate groove is uneven, and the concave and convex units are distributed at intervals, and the distribution is regular and periodically changing. In this device, the bottom of the gate trench has a continuous and gradually changing uneven shape along the gate width direction, which leads to a continuous and gradual change in the distance from the gate bottom to the channel along the gate width direction, making this structure equivalent to many through gates with different gate widths. The devices that drive the static bias voltage are paralleled to each other, and the transconductance derivatives can cancel each other in the linear region, suppress unwanted harmonic factors, suppress the peak behavior of the transconductance in this region, and there is always a conduction device to the other conduction The pass device performs transconductance compensation to deal with the transconductance roll-off near the pinch-off region. This not only enables the HEMT with this structure to obtain a flat transconductance profile with a wide range and good linearity, but also basically does not cause transconductance loss. In addition, the invention reduces the distortion, and at the same time reduces the design complexity and follow-up cost of related pre-distortion circuits.

There are many options for the uneven shape of the bottom of the above gate groove.

Classified by the shape of the common boundary line between the concave unit of the adjacent HEMT device and the convex unit of the HEMT device, the shape includes: the common boundary line is a straight line (the embodiment shown in Figure 2 or 4), an arc (the implementation shown in Figure 3 example) or stepped polylines. In order to improve the linearity of the device to a greater extent, the angle between the shared boundary lines of two adjacent HEMT devices is preferably between 5° and 175°, such as 5° to 20°, 30° to 60°, 80° to 90° °, 100°～180°, etc.

Classified according to the geometric shape of the concave unit and the convex unit, it can be the shape shown in Figure 2, that is, along the cross-sectional direction of the width of the HEMT device gate, the convex unit of the HEMT device is triangular, the concave unit of the HEMT device is an inverted triangle, and the HEMT device The base angle β of the convex unit of the device is preferably between 5° and 175°.

Or the shape shown in Figure 3, along the width direction of the gate of the HEMT device, the bottom of the grid groove of the HEMT device is wavy, the concave unit of the HEMT device is a wave valley, and the convex unit of the HEMT device is a wave peak, for example, a cross section along the width of the gate In the direction, the bottom of the grid groove is sinusoidal.

Or as shown in FIG. 4 , in the cross-sectional direction along the width of the gate of the HEMT device, the top of the convex unit of the HEMT device is a fan-shaped edge, and the concave unit of the HEMT device is an inverted triangle.

In order to improve the linearity of the device to a greater extent, the vertical distance between the apex of the convex unit and the lowest point of the concave unit of the HEMT device is preferably between 20 and 30 nm, and/or, the distance between two adjacent concave units is within 100 μm, As shown in Figures 1 and 2.

The preparation method of the above-mentioned high-linear HEMT device of the present invention is relatively simple, and the pattern of the gate groove is mainly controlled by etching the photoresist and the etching of the barrier layer. layer, AlGaN barrier layer, and SiN passivation layer as examples.

In the first step, the nucleation layer, buffer layer, and barrier layer are sequentially stacked on the provided substrate. The formation method of each layer is not limited, and various deposition methods or sputtering methods may be used.

In the second step, spin-coat electron beam photoresist on the barrier layer, preferably with a thickness of 50 nm, to obtain the morphology shown in FIG. 5 .

The third step is to place dense thin lines on the photoresist, the size range is: 0.01 μm-100 μm, and the line spacing range is: 0.01 μm-100 μm, as shown in Figure 6.

The fourth step is to carry out electron beam lithography, as shown in FIG. 7 .

The fifth step is to perform high-temperature vacuum hot plate reflux for 1-5 minutes at a temperature of 110-150° C., as shown in FIG. 8 .

The sixth step is to apply primer and perform low-damage dry etching, as shown in Figure 9.

The seventh step is to remove the photoresist, as shown in FIG. 10 .

The eighth step, follow-up process: for example, a passivation layer is formed on the barrier layer of the HEMT device, and the passivation layer of the HEMT device does not fill the gate groove of the HEMT device; the gate is fabricated in the gate groove of the HEMT device; source and drain to obtain the device shown in Figure 2.

The above preparation method is only an example, and the process can be adaptively adjusted according to the requirements of the shape of the bottom of the gate groove in actual application.

The embodiments of the present disclosure have been described above. However, these examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. The scope of the present disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the present disclosure, and these substitutions and modifications should all fall within the scope of the present disclosure.

Claims (10)

1. A high linearity HEMT device, comprising:

the buffer layer is formed on the nucleation layer, and the buffer layer is formed on the barrier layer;

the passivation layer is provided with a gate groove, the bottom of the gate groove is positioned in the barrier layer, and a gate is arranged in the gate groove; a source electrode and a drain electrode are respectively arranged on two sides of the grid electrode, and the source electrode and the drain electrode are in ohmic contact with the buffer layer;

the bottom of the gate trench has the following shape: along the width direction of grid, the bottom of grid groove is unsmooth form, by concave unit and protruding unit interval distribution, and be regular periodic variation distribution.

2. The high linearity HEMT device of claim 1, wherein a common boundary line between adjacent ones of said concave cells and said convex cells is a straight line, an arc line or a stepped polygonal line.

3. The high linearity HEMT device of claim 2, wherein the angle between two adjacent common boundary lines is between 5 ° and 175 °.

4. The high linearity HEMT device of claim 1, wherein said convex cells are triangular and said concave cells are inverted triangular in cross-sectional direction along the width of said gate, said convex cells having a base angle between 5 ° and 175 °.

5. The high linearity HEMT device of claim 1, wherein the bottom of the gate trench is wavy along the width direction of the gate, the concave units are troughs, and the convex units are crests.

6. The high linearity HEMT device of claim 1, wherein the top of the convex cell is a scalloped edge and the concave cell is an inverted triangle in a cross-sectional direction along the width of the gate.

7. The high linearity HEMT device of claim 1, wherein a vertical distance between a top point of said convex cell and a lowest point of said concave cell is between 20 and 30 nm.

8. The high linearity HEMT device of claim 1, wherein the pitch of two adjacent recessed cells is within 100 μ ι η.

9. The high linearity HEMT device of any one of claims 1-8, wherein the barrier layer is an AlGaN barrier layer and the buffer layer is a GaN buffer layer.

10. The method for preparing the high linearity HEMT device of any one of claims 1 to 9, comprising:

providing a substrate;

sequentially stacking a nucleating layer, a buffer layer and a barrier layer on a substrate;

spin coating a photoresist on the barrier layer;

etching the photoresist to form a plurality of grooves distributed at intervals, wherein the grooves penetrate through the photoresist;

carrying out high-temperature vacuum hot plate reflux treatment on the photoresist with the groove at the temperature of 110-150 ℃;

carrying out low-damage etching on the barrier layer, and removing the photoresist to form a grid groove with an uneven bottom;

forming a passivation layer on the barrier layer, wherein the passivation layer does not fill the gate trench;

manufacturing a grid in the grid groove;

and respectively manufacturing a source electrode and a drain electrode on two sides of the grid electrode.

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