CN112993033B - GaN device structure and preparation method thereof - Google Patents

Abstract

The invention provides a GaN device structure and a preparation method thereof. The preparation includes: providing a substrate; preparing an epitaxial structure, an auxiliary function part and a device electrode, wherein the auxiliary function structure includes a plurality of stacked p-type doped layers. For the auxiliary unit layer, the doping concentration of the auxiliary doping layer gradually increases from the lower layer to the upper layer. By introducing multi-layer p-type doped auxiliary functional parts with graded concentration, the auxiliary functional parts also serve as the cap layer structure of the device, so that when the gate voltage is continuously increased, holes start to be injected into the channel and an equal number of electrons are generated, Thereby increasing 2DEG. Electrons with high mobility will reach the drain under the action of the electric field, while holes will remain because their mobility is much lower than electrons, so the current is modulated by the number of holes injected, which can be shown in the transconductance curve A double peak, effectively improving the linearity of the device.

Description

GaN device structure and preparation method thereof

technical field

The invention belongs to the technical field of integrated circuit manufacturing, and in particular relates to a GaN device structure and a preparation method thereof.

Background technique

The research and application of GaN materials is currently the frontier and hotspot of global semiconductor research. It is a new type of semiconductor material for the development of microelectronic devices and optoelectronic devices. The third generation of semiconductor materials after semiconductor materials. It has the properties of wide direct band gap, strong atomic bond, high thermal conductivity, good chemical stability (hardly corroded by any acid) and strong radiation resistance.

However, the GaN device has the problem of predistortion nonlinearity during operation due to its material and the characteristics of the device structure. The specific problem is that the research on extending the power output band of GaN HEMTs to submillimeter waves is limited by the nonlinearity of short-channel devices, that is, the frequency fT (or transconductance gm) increases with the bias voltage at high drain voltage (high gate voltage) high drop rapidly, thus limiting the high-speed operation characteristics of the device at high voltage and making the maximum current density significantly lower than the theoretical prediction.

Therefore, it is necessary to provide a GaN device structure and a preparation method thereof to solve the above problems.

SUMMARY OF THE INVENTION

In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a GaN device structure and a preparation method thereof, which are used to solve the problems of predistortion nonlinearity in the GaN device in the prior art, and it is difficult to effectively optimize the linearity. .

In order to achieve the above object and other related objects, the present invention provides a preparation method of a GaN device structure, and the preparation method includes the following steps:

provide a substrate;

forming an epitaxial structure on the substrate, at least including a GaN channel layer and a barrier layer arranged from bottom to top;

An auxiliary functional structure is formed on the epitaxial structure, and the auxiliary functional structure includes several superimposed auxiliary unit layers which are p-type doped layers, and the doping concentration of the auxiliary doped layers gradually increases from the lower layer to the upper layer ;

A gate region is defined on the surface of the auxiliary function structure, and part of the auxiliary function structure at the periphery of the gate region is etched and removed to the barrier layer to obtain an auxiliary function portion corresponding to the gate region;

A source electrode, a drain electrode, and a gate electrode corresponding to the gate region are prepared to obtain the GaN device structure.

Optionally, the auxiliary functional structure includes any one of an AlGaN functional structure and a GaN functional structure, wherein, when the AlGaN functional structure is included, the AlGaN functional structure includes several AlGaN unit layers as the auxiliary unit layer; when the GaN functional structure is included, the GaN functional structure includes several GaN unit layers as the auxiliary unit layers.

Optionally, when the auxiliary functional structure is selected as the AlGaN functional structure, the preparation method further includes the steps of: forming a GaN insertion layer between the AlGaN functional structure and the barrier layer, and forming the AlGaN functional structure. When assisting the functional part, the corresponding GaN insertion layer is also removed.

Optionally, the number of layers of the auxiliary unit layer is n layers, the first layer to the nth layer from bottom to top, n is an integer greater than or equal to 2, wherein the doping of each layer of the auxiliary unit layer is The concentration is between (0.8-1.2)n*10 ¹⁸ /cm ³ , and the total doping concentration of the auxiliary functional structure is between 10 ¹⁸ /cm ³ -10 ¹⁹ /cm ³ , and the total thickness is between 10nm -100nm.

Optionally, the step of defining the gate region on the surface of the epitaxial structure includes: forming an ITO material layer on the surface of the epitaxial structure, and using a photolithography process to define the gate region in the ITO material layer, and removing the ITO material layer around the gate region, and using the ITO material layer in the gate region as a mask for forming the auxiliary function portion.

Optionally, the method for removing part of the auxiliary functional structure at the periphery of the gate region by etching includes: performing etching by using a method of oxidation combined with wet etching.

Optionally, the longitudinal cross-sectional shape of the auxiliary function part is a trapezoid, and the method of preparing the trapezoidal auxiliary function part is as follows: preparing a trapezoidal mask on the auxiliary function structure, and performing the process based on the trapezoidal mask. Etching is performed to transfer the pattern of the trapezoidal mask to the auxiliary function structure to obtain the auxiliary function part.

Optionally, the method of forming the trapezoidal mask is: forming a mask material layer on the auxiliary function structure; using electron beam exposure technology for exposure, wherein the exposure dose is gradually increased from the gate area to both sides. increase; developing the exposed structure to obtain a stepped mask; tempering the stepped mask to obtain the trapezoidal mask.

In addition, the present invention also provides a GaN device structure. The GaN device structure is preferably prepared by the preparation method of the present invention. Of course, other methods can also be used to prepare the GaN device structure, wherein the GaN device structure includes:

substrate;

an epitaxial structure, formed on the substrate, at least including a GaN channel layer and a barrier layer arranged from bottom to top;

an auxiliary function part, a gate region is defined on the surface, the auxiliary function part is formed on the epitaxial structure corresponding to the gate region, wherein the auxiliary function structure includes a plurality of stacked p-type doped layers The auxiliary unit layer, the doping concentration of the auxiliary doping layer gradually increases from the lower layer to the upper layer;

A source electrode, a drain electrode and a gate electrode are formed on the epitaxial structure, and the gate electrode corresponds to the gate region, and the source electrode and the drain electrode are located on the auxiliary peripheral function.

Optionally, the auxiliary functional structure includes any one of an AlGaN functional structure and a GaN functional structure, wherein, when the AlGaN functional structure is included, the AlGaN functional structure includes several AlGaN unit layers as the auxiliary unit layer; when the GaN functional structure is included, the GaN functional structure includes several GaN unit layers as the auxiliary unit layers.

Optionally, the number of layers of the auxiliary unit layer is n layers, and the layers are from the first layer to the nth layer from bottom to top, and n is an integer greater than or equal to 2, wherein the doping amount of each layer of the auxiliary unit layer is The impurity concentration is between (0.8-1.2)n*10 ¹⁸ /cm ³ , and the total doping concentration of the auxiliary functional structure is between 10 ¹⁸ /cm ³ -10 ¹⁹ /cm ³ , and the total thickness is between Between 10nm-100nm.

Optionally, the longitudinal cross-sectional shape of the auxiliary function part is a trapezoid.

As described above, in the GaN device structure and its preparation method of the present invention, by introducing multi-layer p-type doping and concentration-graded auxiliary functional parts, the auxiliary functional parts simultaneously serve as the cap layer structure of the device, so that when the gate voltage is continuously increased , holes start to inject into the channel and generate an equal number of electrons, thereby increasing the 2DEG. Electrons with high mobility will reach the drain under the action of the electric field, while holes will remain because their mobility is much lower than electrons, so the current is modulated by the number of holes injected, which can be shown in the transconductance curve A double peak, effectively improving the linearity of the device. In addition, the present invention also introduces a trapezoidal design based on hole injection, which further improves the linearity of the device.

Description of drawings

FIG. 1 shows a flow chart of the fabrication of the GaN device structure provided by the present invention.

2-8 are schematic diagrams showing the structures obtained by each step in the preparation of the GaN device structure provided by the present invention.

Figure 9 shows the simulation curves of a GaN device designed for a multi-layer graded-based secondary function structure.

Figure 10 shows simulation curves for a GaN device designed for a singly doped secondary function structure.

FIG. 11 shows simulation curves of GaN devices designed for auxiliary function sections of square longitudinal section and trapezoidal longitudinal section.

12-14 are schematic diagrams showing the steps of forming a ladder mask in the fabrication of an exemplary GaN device structure of the present invention.

Component label description

101 Substrate

102 Buffer layer

103 GaN functional layer

104 Barrier layer

105 Accessibility structure

106 ITO structure

107 Accessibility Department

108 Source electrode

109 Drain electrode

110 Gate electrode

S1～S5 steps

Detailed ways

The embodiments of the present invention are described below through specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

When describing the embodiments of the present invention in detail, for the convenience of explanation, the cross-sectional views showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the protection scope of the present invention. In addition, the three-dimensional spatial dimensions of length, width and depth should be included in the actual production.

For convenience of description, spatially relative terms such as "below," "below," "below," "below," "above," "on," etc. may be used herein to describe an element shown in the figures or The relationship of a feature to other components or features. It will be understood that these spatially relative terms are intended to encompass other directions of the device in use or operation than those depicted in the figures. In addition, when a layer is referred to as being 'between' two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Additionally, "between" as used in the present invention includes both endpoints.

In the context of this application, descriptions of structures where a first feature is "on" a second feature can include embodiments in which the first and second features are formed in direct contact, and can also include further features formed over the first and second features. Embodiments between the second features such that the first and second features may not be in direct contact.

It should be noted that the diagrams provided in this embodiment are only to illustrate the basic concept of the present invention in a schematic way, so the diagrams only show the components related to the present invention rather than the number, shape and the number of components in the actual implementation. For dimension drawing, the type, quantity and proportion of each component can be arbitrarily changed in actual implementation, and the component layout may also be more complicated.

As shown in FIG. 1, the present invention provides a preparation method of a GaN device structure, and the preparation method includes the following steps:

S1, provide the substrate;

S2, forming an epitaxial structure on the substrate, including at least a GaN channel layer and a barrier layer arranged from bottom to top;

S3, forming an auxiliary function structure on the epitaxial structure, the auxiliary function structure including a plurality of superimposed auxiliary unit layers which are p-type doped layers, and the doping concentration of the auxiliary doped layers is from the lower layer to the upper layer gradually increase;

S4, define a gate region on the surface of the auxiliary function structure, and etch and remove part of the auxiliary function structure around the gate region to the barrier layer to obtain auxiliary functions corresponding to the gate region department;

S5, preparing a source electrode, a drain electrode and a gate electrode corresponding to the gate region to obtain the GaN device structure.

The preparation method of the GaN device structure of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the above sequence does not strictly represent the preparation sequence of the GaN device structure protected by the present invention, and those skilled in the art can refer to the actual process. The steps are changed, and FIG. 1 only shows the fabrication steps of the GaN device structure in one example of the present invention.

First, as shown in S1 and FIG. 2 in FIG. 1 , step S1 is performed to provide a substrate 101 .

Specifically, the substrate 101 may be a silicon (Si) substrate, a germanium (Ge) substrate, a silicon germanium (SiGe) substrate, an SOI substrate or a GOI (Germanium-on-Insulator, germanium-on-insulator) substrate A substrate, a SiC substrate, a sapphire (Sapphire) substrate, a GaN substrate, etc., are preferably SiC, GaN, Sapphire, or Si substrates. In other examples, the substrate 101 may also be a substrate including other semiconductor elements or compounds, such as gallium arsenide, indium phosphide, or silicon carbide, etc., and the substrate 101 may also be a stacked structure, such as silicon /GeSi stack, etc. In this embodiment, the substrate 101 is a Si(111) substrate. Using silicon as the substrate, the heteroepitaxy of GaN material can be realized on a large-sized wafer, saving the unit size extension cost.

Next, as shown in S2 and FIG. 4 in FIG. 1 , step S2 is performed to form an epitaxial structure on the substrate 101 , and the epitaxial structure at least includes a GaN channel layer 103 and a barrier layer arranged from bottom to top 104. In addition, the formation process of each material layer in the epitaxial structure includes, but is not limited to, an epitaxial process.

In an example, before forming the GaN channel layer 103, it further includes the step of forming a buffer layer 102 for relieving lattice mismatch, wherein the thickness of the GaN channel layer 103 may be between 100nm-1um, For example, it may be 200 nm, 500 nm, or 800 nm. The buffer layer 102 includes, but is not limited to, an AlGaN layer, and the thickness may be between 1-3um, such as 1.5um, 2um, and 2.5um. In addition, the barrier layer 104 includes, but is not limited to, an AlGaN layer, and the thickness may be between 10-30 nm, for example, may be 15 nm, 20 nm, or 25 nm.

Next, as shown in S3 and FIG. 4 in FIG. 1 , step S3 is performed to form an auxiliary function structure 105 on the epitaxial structure, and the auxiliary function structure 105 includes several stacked auxiliary unit layers, such as auxiliary unit layers. 105a, 105b, 105c, the auxiliary unit layer is a p-type doped layer, and in addition, the doping concentration of each auxiliary doped layer of the auxiliary functional structure gradually increases from bottom to top. That is to say, in an example, the doping concentration of each auxiliary unit layer may be uniform doping, the doping concentration between different layers is different, and the doping concentration of the upper layer between adjacent auxiliary unit layers is large. In addition, the formation process of the auxiliary function structure 105 includes, but is not limited to, an epitaxy process.

Specifically, the auxiliary function structure 105 formed on the barrier layer 104 can also serve as a cap layer of the device. In addition, through the design of the auxiliary function structure 105 with p-type doping, when the gate voltage is continuously increased, holes start to be injected into the channel and an equal number of electrons are generated, thereby increasing the 2DEG. Electrons with high mobility will reach the drain under the action of the electric field, while holes will remain because their mobility is much lower than electrons. Therefore, the current is modulated by the number of holes injected. and shows a double peak in the transconductance curve. Referring to FIG. 9 and FIG. 10 , FIG. 9 shows the simulation curve (transconductance curve) of a GaN device designed by using the multi-layer graded auxiliary function structure of the present invention. In addition, FIG. 10 shows a single-layer single-doping The obtained simulation curve (transconductance curve) was used as a control. It can be seen that the bimodal curves are obtained in the two figures respectively, and the second one is the gm peak generated by the injection of holes. Through the auxiliary functional structure of the P-type doping of the present invention, the linearity of the device can be improved. The scheme of the auxiliary functional structure design can gradually inject holes, make the gm flattening more obvious, the drop between the two peaks is alleviated, and the gm flattening is further improved, thereby improving the linearity of the device.

As an example, the auxiliary functional structure 105 includes any one of an AlGaN functional structure and a GaN functional structure. That is, the auxiliary functional structure may be composed of only the AlGaN functional structure, may be composed of only the GaN functional structure, or may be composed of both. It is preferable to employ any one of the two configurations.

In an example, the auxiliary functional structure 105 is only composed of the AlGaN functional structure. Specifically, the AlGaN functional structure includes several AlGaN unit layers as the auxiliary unit layers, such as the auxiliary unit layers 105a and 105b. , 105c.

In another example, the auxiliary functional structure 105 is only composed of the GaN functional structure, specifically, the GaN functional structure includes several GaN unit layers, as the auxiliary unit layers, for example, the auxiliary unit layers 105a, 105b, 105c.

In a further example, when the auxiliary functional structure 105 is selected as the AlGaN functional structure, the preparation method further includes forming a GaN insertion layer (not shown in the figure) between the AlGaN functional structure and the barrier layer 104 out), and the corresponding GaN insertion layer is also removed when the auxiliary function part is formed. Specifically, the GaN insertion layer can be used as a selective etching stop layer, and the thickness can be between 1-5 nm, for example, it can be designed to be 2 nm, 3 nm, or 4 nm. For example, a GaN layer is inserted between the AlGaN barrier and the p-AlGaN cap layer.

As an example, the number of layers of the auxiliary unit layer is n layers, and the layers are from the 1st layer to the nth layer from bottom to top, and n is an integer greater than or equal to 2. For example, it is shown as 3 layers in FIG. : the first auxiliary unit layer 105a, the second auxiliary unit layer 105b, and the third auxiliary unit layer 105c. Wherein, the concentration of each auxiliary unit layer is increased linearly, which improves the stability and repeatability of the process.

In an example, the doping concentration of each of the auxiliary unit layers is (0.8-1.2)n*10 ¹⁸ /cm ³ . That is, the doping concentration of each of the auxiliary unit layers may be 0.9n*10 ¹⁸ /cm ³ , n*10 ¹⁸ /cm ³ , and 1.1n*10 ¹⁸ /cm ³ . Correspondingly, taking three auxiliary unit layers as an example, in an example, the doping concentration of each layer is: the first auxiliary unit layer 105a is 0.9*10 ¹⁸ /cm ³ ; the second auxiliary unit layer 105b is 1.8* 10 ¹⁸ /cm ³ ; the third auxiliary unit layer 105c is 2.7*10 ¹⁸ /cm ³ . In another example, the doping concentration of each layer is: the first auxiliary unit layer 105a is 1*10 ¹⁸ /cm ³ ; the second auxiliary unit layer 105b is 2*10 ¹⁸ /cm ³ ; the third auxiliary unit layer is 2*10 18 /cm 3 Layer 105c is 3*10 ¹⁸ /cm ³ . In another example, the doping concentration of each layer is: the first auxiliary unit layer 105a is 1.1*10 ¹⁸ /cm ³ ; the second auxiliary unit layer 105b is 2.2*10 ¹⁸ /cm ³ ; the third auxiliary unit layer is 2.2*10 18 /cm 3 . The layer 105c is 3.3*10 ¹⁸ /cm ³ . And so on for other layers.

In a further example, the total doping concentration of the auxiliary functional structures 105 is between 10 ¹⁸ /cm ³ -10 ¹⁹ /cm ³ , that is, the sum of the doping concentrations in each auxiliary unit layer is between 10 ¹⁸ /cm 3 Between ³ -10 ¹⁹ /cm ³ . For example, it may be 2*10 ¹⁸ /cm ³ , 5*10 ¹⁸ /cm ³ , 8*10 ¹⁸ /cm ³ . In another optional example, the total thickness of the auxiliary function structure 105 is between 10 nm and 100 nm, for example, it may be 20 nm, 50 nm, 60 nm, or 80 nm. It is beneficial to ensure the gate control ability and alleviate the short channel effect.

Next, as shown in S4 in FIG. 1 and FIGS. 5-6 , step S4 is performed, a gate region is defined on the surface of the auxiliary function structure 105 , and a part of the auxiliary function in the periphery of the gate region is etched correspondingly The structure 105 is connected to the barrier layer 104 to obtain an auxiliary function portion 107 corresponding to the gate region.

As an example, referring to FIGS. 7 and 8 , the longitudinal cross-sectional shape of the auxiliary function part 107 may be a square, as shown in FIG. 7 , or a trapezoid, as shown in FIG. 8 . In a preferred example, the longitudinal cross-sectional shape of the auxiliary function part 107 is selected as a trapezoid, and the simulation structure of the transconductance curve is shown in FIG. , which is more conducive to linear optimization. In addition, taking the auxiliary function structure 105 having three auxiliary unit layers 105a, 105b and 105c as an example, after the auxiliary function part 107 is obtained by etching, the first auxiliary unit layer 105a is converted into the first function part unit 107a, The second auxiliary unit layer 105b is converted into the second functional unit unit 107b, and the third auxiliary unit layer 105c is converted into the third functional unit unit 107c.

In an example, the auxiliary function part 107 may be formed by: as shown in FIG. 5 , now an ITO (Indium-Tin-Oxide) material layer is deposited on the surface of the auxiliary function structure 105 , and the thickness may be between 100 Between -500nm, for example, 200nm and 300nm are selected; then, the gate region is defined by a photolithography process, and the excess ITO material layer is removed by wet etching to form an ITO structure 106, which can be used as a gate metal layer, which can be used together as a part of the subsequent gate electrode; then, as shown in FIG. 6 , and referring to the structure shown in FIG. 8 , the ITO structure 106 is used as a mask to remove the excess in the auxiliary function structure 105 material layer to obtain the auxiliary function part 107 for device modification. In this example, the ITO layer is compatible with the GaN optoelectronic device process, and as a transparent electrode, it can be characterized by related optical methods. In addition, the subsequent fabrication of the source electrode and the drain electrode (eg, fabricated by using Ni/Au) has less process restrictions, and the fabrication efficiency and reliability of the device can also be improved.

In another example, the auxiliary function portion 107 may also be formed in the following way: first, a photolithography mask is used to define the gate region, and after etching the auxiliary function structure and the preparation of the source and drain ohmic contacts, to obtain The source electrode and drain electrode, and then the gate Ni/Au deposition is performed to obtain the gate electrode. In this method, since Ni/Au cannot withstand the high temperature annealing during the preparation of the source and drain electrodes, Ni will penetrate into the semiconductor potential. barrier, which affects the reliability of the device, so the gate electrode is formed subsequently.

As an example, the auxiliary function portion 107 may be formed by etching: first, the auxiliary function structure is etched by an etching process, and then the auxiliary function structure is etched by an oxidation combined with a wet etching method until the potential is reached. barrier layer.

In one example, most of the p-doped AlGaN or GaN is removed by ICP etching, for example, until the last auxiliary cell layer remains, such as the first auxiliary cell layer 105a, or, when the auxiliary function When the structure is composed of several AlGaN layers additionally provided with a GaN insertion layer, the GaN insertion layer is etched by ICP. Further, continue to etch (etch away the remaining GaN layer) to the barrier layer (eg, the AlGaN layer) by means of oxidation combined with wet etching.

Wherein, in a specific example, the method of oxidation combined with wet etching may be to use O2 plasma or ozone O3 to oxidize to form Ga-O, and then use acidic chemical reagents such as HCl to remove the oxide layer until the surface of the barrier layer.

In addition, when the longitudinal cross-sectional shape of the auxiliary function portion 107 is a trapezoid, the formation method of the auxiliary function portion 107 may be further optimized. The method is as follows: prepare a trapezoidal mask 203 on the auxiliary function structure 105 , and perform etching based on the trapezoidal mask 203 to transfer the pattern of the trapezoidal mask 203 to the auxiliary function structure 105 , the trapezoidal auxiliary function part 107 is obtained.

In a specific example, referring to FIGS. 12-14 , a specific method for preparing the trapezoidal mask 203 is provided:

First, as shown in FIG. 12 , a mask material layer 201 (photoresist resin) is formed on the auxiliary function structure 105; the material of the mask material layer 201 can be PMMA, for example, its thickness can be between 500nm-1μm, or is 600nm, 800nm;

Next, continue to refer to FIG. 12 , use electron beam exposure technology (E-beam) for exposure, wherein the exposure dose gradually increases from the gate region (corresponding to the ITO structure in the figure) to both sides; for example, the gate region The exposure dose inside can be chosen to be the same. In a specific example, the exposure dose is gradually increased from the center to both sides, such as from 300uc/cm ² to 500uc/cm ² , and in a further example, the exposure dose can be linearly increased;

Next, as shown in FIG. 13, the exposed structure is developed to obtain a step mask 202, which can be MIBK development;

Finally, as shown in FIG. 14 , the stepped mask 202 is tempered to obtain the trapezoidal mask 203 ; in an example, the tempering process may be: at 110-130° C. 120° C.) annealing in a temperature atmosphere for 1-10 minutes (for example, 2 minutes, 5 minutes) to form a desired smooth beveled-edge mask to obtain the trapezoidal mask 203 .

In another example, the method of preparing the trapezoidal auxiliary functional portion 107 may also be to use electrochemical anisotropic etching, and use the characteristic that the higher the doping concentration, the faster the etching rate, to obtain the assistance of the trapezoidal structure The functional part can simplify the process. For example, for the GaN auxiliary functional structure, an Acidic chemical reagent can be used, the sample is immersed in the reagent, and then the electrode placed in the reagent can be biased to perform electrochemical wet etching. The electrochemical etching method is beneficial to For the effective etching of the GaN auxiliary function part, when the auxiliary function part is selected to be a GaN functional structure, an electrochemical etching method is used.

Finally, as shown in S5 in FIG. 1 and FIGS. 7-8 , step S5 is performed to prepare the source electrode 108 , the drain electrode 109 and the gate electrode 110 on the epitaxial structure to obtain the GaN device structure.

Specifically, when the gate region is defined based on the ITO material layer, the obtained ITO structure 106 and the gate electrode 110 are electrically extracted together as the gate structure. When a photoresist mask is used to define the gate region, the gate electrode 110 is directly formed on the surface of the auxiliary function part 107 . Among them, in a specific example, using photolithography, define the source and drain regions, deposit metal, lift off, form source and drain electrodes, and anneal under N2 at 800°C-900°C (eg 850°C) for 25s-35s (eg 30s) ), and at the same time complete the ITO gate and source and drain preparations. Of course, other processes can also be used to prepare the respective device electrodes.

In an example, when the auxiliary function portion 107 with a trapezoidal cross-section is obtained, the long side (the side in contact with the barrier layer) of the auxiliary function portion 107 of the trapezoid extends to the source electrode and the source electrode of the two The drain electrodes are in contact, that is, the trapezoidal structure has an edge linear contact with the surfaces of the two electrodes in contact with the barrier layer, so as to facilitate effective stepwise hole injection.

As an example, after forming the source electrode 108, the drain electrode 109 and the gate electrode 110, the step further includes: depositing a SiN layer by a CVD process or depositing an Al2O3 layer by an ALD process as a device passivation layer to passivate the device surface. Of course, it is also possible to form an Al2O3 layer first, and then form a SiN layer on the surface of the Al2O3 layer.

In addition, as shown in Figures 7 and 8, and referring to Figures 1-6 and Figures 9-11, the present invention also provides a GaN device structure, the GaN device structure is preferably prepared by the preparation method of the present invention, of course , can also be prepared by other methods, wherein, for the features in the GaN device structure, reference may be made to the description in the preparation method of this embodiment, which will not be repeated here.

The GaN device structure of this embodiment includes:

substrate 101;

an epitaxial structure, formed on the substrate, at least including a GaN channel layer 103 and a barrier layer 104 arranged from bottom to top;

The auxiliary function part 107 has a gate region defined on its surface, and the auxiliary function part is formed on the epitaxial structure corresponding to the gate region, wherein the auxiliary function structure includes several stacked and p-type doped The auxiliary unit layer of the layer, the doping concentration of the auxiliary doping layer gradually increases from the lower layer to the upper layer;

A source electrode 108, a drain electrode 109 and a gate electrode 110 are formed on the epitaxial structure, and the gate electrode corresponds to the gate region, and the source electrode and the drain electrode are located at The auxiliary function part 107 is peripheral.

As an example, the auxiliary functional structure 105 includes any one of an AlGaN functional layer and a GaN functional layer, wherein, when the AlGaN functional layer is included, the AlGaN functional layer includes several AlGaN unit layers as the auxiliary unit layer; when the GaN functional layer is included, the GaN functional layer includes several GaN unit layers as the auxiliary unit layer.

As an example, the number of layers of the auxiliary unit layer is n, and from bottom to top, the first layer to the nth layer are respectively, and n is an integer greater than or equal to 2, wherein the doping of each layer of the auxiliary unit layer is The concentration is (0.8-1.2)n*10 ¹⁸ /cm ³ , and the total doping concentration of the auxiliary functional structure is between 10 ¹⁸ /cm ³ -10 ¹⁹ /cm ³ , and the total thickness is between 10nm-100nm between.

As an example, the longitudinal cross-sectional shape of the auxiliary function part 107 is a trapezoid.

To sum up, in the GaN device structure and its preparation method of the present invention, by introducing a multi-layer p-type doped auxiliary function part with gradient concentration, the auxiliary function part also serves as the cap layer structure of the device, which can make the gate voltage constant when the gate voltage is constant. When increasing, holes start to inject into the channel and generate an equal number of electrons, thereby increasing the 2DEG. Electrons with high mobility will reach the drain under the action of the electric field, while holes will remain because their mobility is much lower than electrons, so the current is modulated by the number of holes injected, which can be shown in the transconductance curve A double peak, effectively improving the linearity of the device. In addition, the present invention also introduces a trapezoidal design based on hole injection, which further improves the linearity of the device. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial application value.

The above-mentioned embodiments merely illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Anyone skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed in the present invention should still be covered by the claims of the present invention.

Claims (12)

1. A preparation method of a GaN device structure is characterized by comprising the following steps:

providing a substrate;

forming an epitaxial structure on the substrate, wherein the epitaxial structure at least comprises a GaN channel layer and a barrier layer which are arranged from bottom to top;

forming an auxiliary function structure on the epitaxial structure, wherein the auxiliary function structure comprises auxiliary unit layers of which n layers are p-type doped layers and are respectively from the 1 st layer to the nth layer from bottom to top, n is an integer more than or equal to 2, and the doping concentration of each unit layer is (0.8-1.2) n ﹡ 10¹⁸/cm³The doping concentration of the auxiliary unit layer is gradually increased from the lower layer to the upper layer;

defining a gate region on the surface of the auxiliary function structure, and etching and removing part of the auxiliary function structure at the periphery of the gate region to the barrier layer to obtain an auxiliary function part corresponding to the gate region;

and preparing a source electrode, a drain electrode and a gate electrode corresponding to the gate region to obtain the GaN device structure.

2. The method of claim 1, wherein the auxiliary functional structure comprises any one of an AlGaN functional structure and a GaN functional structure, wherein when the AlGaN functional structure is included, the AlGaN functional structure comprises a plurality of AlGaN unit layers as the auxiliary unit layers; when the GaN functional structure is included, the GaN functional structure includes a plurality of GaN unit layers as the auxiliary unit layers.

3. The method of claim 2, wherein when the auxiliary functional structure is selected to be the AlGaN functional structure, the method further comprises the steps of: forming a GaN insertion layer between the AlGaN functional structure and the barrier layer.

4. The method of claim 1, wherein the auxiliary functional structure has a total doping concentration of 10¹⁸/cm³-10¹⁹/cm³And the total thickness is between 10nm and 100 nm.

5. The method of claim 1, wherein the step of defining the gate region on the surface of the epitaxial structure comprises: forming an ITO material layer on the surface of the epitaxial structure, defining a gate region in the ITO material layer by utilizing a photoetching process, removing the ITO material layer around the gate region, and taking the ITO material layer of the gate region as a mask for forming the auxiliary function part for etching.

6. The method for preparing the GaN device structure of claim 1, wherein the manner of etching away the auxiliary functional structure at the periphery of the gate region comprises: and etching the auxiliary functional structure by adopting an etching process, and continuously etching to the barrier layer by adopting a mode of combining oxidation and wet etching.

7. The method of any of claims 1-6, wherein the auxiliary functional portion has a trapezoidal longitudinal cross-sectional shape, and wherein the trapezoidal auxiliary functional portion is prepared by: and preparing a trapezoidal mask on the auxiliary function structure, and etching based on the trapezoidal mask so as to transfer the pattern of the trapezoidal mask to the auxiliary function structure to obtain the auxiliary function part.

8. The method of claim 7, wherein the trapezoidal mask is formed by: forming a mask material layer on the auxiliary functional structure; exposing by adopting an electron beam exposure technology, wherein the exposure dose is gradually increased from the gate region to two sides; developing the exposed structure to obtain a step type mask plate; and tempering the stepped mask to obtain the trapezoidal mask.

9. A GaN device structure, comprising:

a substrate;

the epitaxial structure is formed on the substrate and at least comprises a GaN channel layer and a barrier layer which are arranged from bottom to top;

an auxiliary function part, the surface of which is defined with a gate region, the auxiliary function part is formed on the epitaxial structure corresponding to the gate region, wherein the auxiliary function part comprises auxiliary unit layers with n layers being p-type doped layers and respectively from the 1 st layer to the n th layer from bottom to top, n is an integer greater than or equal to 2, and the doping concentration of each unit layer is (0.8-1.2) n ﹡ 10¹⁸/cm³The doping concentration of the auxiliary unit layer is gradually increased from the lower layer to the upper layer;

and the source electrode, the drain electrode and the gate electrode are formed on the epitaxial structure, the gate electrode corresponds to the gate region, and the source electrode and the drain electrode are positioned at the periphery of the auxiliary function part.

10. The GaN device structure of claim 9 wherein the auxiliary functional structure comprises any one of an AlGaN functional structure and a GaN functional structure, wherein when the AlGaN functional structure is included, the AlGaN functional structure comprises a plurality of AlGaN unit layers as the auxiliary unit layers; when the GaN functional structure is included, the GaN functional structure includes a plurality of GaN unit layers as the auxiliary unit layers.

11. The GaN device structure of claim 9 wherein the auxiliary functional structure has a total doping concentration of between 10¹⁸/cm³-10¹⁹/cm³And the total thickness is between 10nm and 100 nm.

12. The GaN device structure of any of claims 9-11 wherein the auxiliary function portion has a trapezoidal longitudinal cross-sectional shape.

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