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

GaN device structure and preparation method thereof Download PDF

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CN112993033B
CN112993033B CN202110181529.8A CN202110181529A CN112993033B CN 112993033 B CN112993033 B CN 112993033B CN 202110181529 A CN202110181529 A CN 202110181529A CN 112993033 B CN112993033 B CN 112993033B
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auxiliary
layer
gan
functional structure
auxiliary function
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CN112993033A (en
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莫炯炯
郁发新
吕贝贝
赵文杰
郎加顺
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Zhejiang University ZJU
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Zhejiang University ZJU
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
    • H01L29/76—Unipolar devices, e.g. field effect transistors
    • H01L29/772—Field effect transistors
    • H01L29/778—Field effect transistors with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface
    • H01L29/7782—Field effect transistors with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface with confinement of carriers by at least two heterojunctions, e.g. DHHEMT, quantum well HEMT, DHMODFET
    • H01L29/7783—Field effect transistors with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface with confinement of carriers by at least two heterojunctions, e.g. DHHEMT, quantum well HEMT, DHMODFET using III-V semiconductor material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/66007—Multistep manufacturing processes
    • H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
    • H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
    • H01L29/66409—Unipolar field-effect transistors
    • H01L29/66446—Unipolar field-effect transistors with an active layer made of a group 13/15 material, e.g. group 13/15 velocity modulation transistor [VMT], group 13/15 negative resistance FET [NERFET]
    • H01L29/66462—Unipolar field-effect transistors with an active layer made of a group 13/15 material, e.g. group 13/15 velocity modulation transistor [VMT], group 13/15 negative resistance FET [NERFET] with a heterojunction interface channel or gate, e.g. HFET, HIGFET, SISFET, HJFET, HEMT

Abstract

The invention provides a GaN device structure and a preparation method thereof, and the preparation method comprises the following steps: providing a substrate; the method comprises the steps of preparing an epitaxial structure, an auxiliary function part and a device electrode, wherein the auxiliary function structure comprises a plurality of superposed auxiliary unit layers which are p-type doped layers, and the doping concentration of the auxiliary doped layers is gradually increased from the lower layer to the upper layer. By introducing the auxiliary function part with p-type doping and gradient concentration, the auxiliary function part is simultaneously used as a cap layer structure of the device, so that when the grid voltage is increased continuously, holes are injected into a channel and generate electrons with equal quantity, and the 2DEG is increased. Electrons with high mobility will reach the drain under the influence of an electric field, while holes will remain, since their mobility is much lower than that of electrons, so that the current is modulated by the number of holes injected, which can show a double peak in the transconductance curve, 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 particularly relates to a GaN device structure and a preparation method thereof.
Background
The research and application of GaN materials are leading edge and hot spot of the current global semiconductor research, are novel semiconductor materials for developing microelectronic devices and optoelectronic devices, and are known as the third generation semiconductor materials following the first generation Ge, Si semiconductor materials, the second generation GaAs and InP compound semiconductor materials. It has wide direct band gap, strong atom bond, high heat conductivity, high chemical stability, etc. and strong radiation resistance.
However, due to the characteristics of the material and the structure of the GaN device, the GaN device has the problem of predistortion nonlinearity during operation. The specific problem is that the research of extending the power output frequency band of the GaN HEMT to the submillimeter wave is limited by the nonlinearity of a short-channel device, namely the frequency fT (or transconductance gm) rapidly decreases along with the increase of bias voltage under high drain voltage (high gate voltage), so that the high-speed working characteristic of the device under high voltage is limited, and the maximum current density is obviously lower than the theoretical predicted value.
Therefore, how to provide a GaN device structure and a method for fabricating the same to solve the above problems is necessary.
Disclosure of Invention
In view of the above drawbacks of the prior art, an object of the present invention is to provide a GaN device structure and a method for manufacturing the same, which are used to solve the problems of non-linearity of predistortion, difficulty in effective optimization of linearity, and the like of GaN devices in the prior art.
To achieve the above and other related objects, the present invention provides a method for fabricating a GaN device structure, the method comprising the steps of:
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 a plurality of superposed auxiliary unit layers which are p-type doped layers, and the doping concentration of the auxiliary doped layers 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.
Optionally, the auxiliary functional structure includes any one of an AlGaN functional structure and a GaN functional structure, where when the AlGaN functional structure is included, the AlGaN functional structure includes 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.
Optionally, when the auxiliary functional structure is selected as the AlGaN functional structure, the preparation method further includes the steps of: and forming a GaN insertion layer between the AlGaN functional structure and the barrier layer, and removing the corresponding GaN insertion layer when the auxiliary functional part is formed.
Optionally, the number of the auxiliary unit layers is n, from 1 st layer to nth layer from bottom to top, n is greater than or equal to2, wherein each of said layers of auxiliary units has a doping concentration of (0.8-1.2) n 1018/cm3And the total doping concentration of the auxiliary functional structure is between 1018/cm3-1019/cm3And the total thickness is between 10nm and 100 nm.
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, defining the 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.
Optionally, the manner of removing part of the auxiliary functional structure at the periphery of the gate region by etching includes: and etching by adopting a mode of combining oxidation and wet etching.
Optionally, the auxiliary function portion has a trapezoidal longitudinal cross-sectional shape, and the manner of preparing the trapezoidal auxiliary function portion is as follows: 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.
Optionally, the manner of forming the trapezoid mask is as follows: 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.
In addition, the present invention also provides a GaN device structure, which is preferably prepared by the preparation method of the present invention, and of course, can also be prepared by other methods, wherein the GaN device structure comprises:
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;
the epitaxial structure comprises an auxiliary function part, a plurality of epitaxial layers and a plurality of auxiliary unit layers, wherein the surface of the auxiliary function part is defined with a gate region, the auxiliary function part is formed on the epitaxial structure corresponding to the gate region, the auxiliary function structure comprises a plurality of superposed auxiliary unit layers which are p-type doped layers, and the doping concentration of the auxiliary doped layers 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.
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 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.
Optionally, the number of the auxiliary unit layers is n, and the auxiliary unit layers are respectively from 1 st layer to nth layer from bottom to top, n is an integer greater than or equal to 2, wherein the doping concentration of each auxiliary unit layer is (0.8-1.2) n 1018/cm3And the total doping concentration of the auxiliary functional structure is between 1018/cm3-1019/cm3And the total thickness is between 10nm and 100 nm.
Optionally, the auxiliary function portion has a trapezoidal longitudinal sectional shape.
As described above, according to the GaN device structure and the preparation method thereof of the present invention, by introducing the multi-layer p-type doped and concentration-graded auxiliary function part, which is simultaneously used as the cap layer structure of the device, when the gate voltage is increased, holes start to be injected into the channel and generate an equal number of electrons, thereby increasing the 2 DEG. Electrons with high mobility will reach the drain under the influence of an electric field, while holes will remain, since their mobility is much lower than that of electrons, so that the current is modulated by the number of holes injected, which can show a double peak in the transconductance curve, effectively improving the linearity of the device. In addition, the invention also introduces a trapezoidal design based on hole injection, and further improves the linearity of the device.
Drawings
FIG. 1 shows a flow chart for the fabrication of a GaN device structure provided by the present invention.
Fig. 2-8 show schematic diagrams of structures obtained in various steps in the fabrication of the GaN device structure provided by the present invention.
Fig. 9 shows a simulation curve of a GaN device designed based on a multi-layer graded auxiliary functional structure.
Fig. 10 shows simulation curves of GaN devices designed based on singly doped auxiliary functional structures.
Fig. 11 shows simulation curves of the GaN device designed for the auxiliary function portion of the square-shaped longitudinal section and the trapezoidal longitudinal section.
FIGS. 12-14 are schematic structural views illustrating steps of forming a trapezoidal mask in fabrication of an exemplary GaN device structure of the invention.
Description of the element reference numerals
101 substrate
102 buffer layer
103 GaN functional layer
104 barrier layer
105 auxiliary function structure
106 ITO structure
107 auxiliary function part
108 source electrode
109 drain electrode
110 gate electrode
S1-S5
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
As in the detailed description of the embodiments of the present invention, the cross-sectional views illustrating the device structures are not partially enlarged in general scale for convenience of illustration, and the schematic views are only examples, which should not limit the scope of the present invention. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual fabrication.
For convenience in description, spatial relational terms such as "below," "beneath," "below," "under," "over," "upper," and the like may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that these terms of spatial relationship are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the figures. Further, 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. In addition, "between … …" as used herein includes both endpoints.
In the context of this application, a structure described as having a first feature "on" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed in between the first and second features, such that the first and second features may not be in direct contact.
It should be noted that the drawings provided in the present embodiment are only for schematically illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than being drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of each component in actual implementation may be changed arbitrarily, and the layout of the components may be more complicated.
As shown in fig. 1, the present invention provides a method for fabricating a GaN device structure, the method comprising the steps of:
s1, providing a substrate;
s2, 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;
s3, forming an auxiliary function structure on the epitaxial structure, wherein the auxiliary function structure comprises a plurality of superposed auxiliary unit layers which are p-type doped layers, and the doping concentration of the auxiliary doped layers is gradually increased from the lower layer to the upper layer;
s4, defining a gate region on the surface of the auxiliary function structure, and etching to remove 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 S5, preparing a source electrode, a drain electrode and a gate electrode corresponding to the gate region to obtain the GaN device structure.
The following will describe the method for fabricating the GaN device structure in detail with reference to the accompanying drawings, wherein it should be noted that the above sequence does not strictly represent the fabrication sequence of the GaN device structure protected by the present invention, and the skilled person can change the sequence according to the actual process steps, and fig. 1 shows only the fabrication steps of the GaN device structure in one example of the present invention.
First, as shown in S1 in fig. 1 and fig. 2, step S1 is performed to provide the 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) substrate, an SiC substrate, a Sapphire (Sapphire) substrate, a GaN substrate, or the like, and is preferably an SiC, GaN, Sapphire, Si substrate. In other examples, the substrate 101 may also be a substrate including other semiconductor elements or compounds, such as gallium arsenide, indium phosphide, silicon carbide, or the like, and the substrate 101 may also be a stacked structure, such as a silicon/germanium-silicon stacked layer, and in this embodiment, the substrate 101 is a Si (111) substrate, and by using silicon as the substrate, heteroepitaxy of GaN materials can be realized on a large-sized wafer, so that the epitaxial cost per unit size is saved.
Next, as shown in S2 in fig. 1 and fig. 4, step S2 is performed to form an epitaxial structure on the substrate 101, the epitaxial structure including at least the GaN channel layer 103 and the barrier layer 104 provided from bottom to top. In addition, the formation process of the various material layers in the epitaxial structure includes, but is not limited to, an epitaxial process.
In an example, the forming of the GaN channel layer 103 further includes a step of forming a buffer layer 102 for alleviating lattice mismatch, wherein the thickness of the GaN channel layer 103 may be between 100nm and 1um, for example, 200nm, 500nm, 800 nm. The buffer layer 102 includes, but is not limited to, an AlGaN layer, and can have a thickness of between 1-3um, such as 1.5um, 2um, or 2.5 um. Additionally, the barrier layer 104 includes, but is not limited to, an AlGaN layer, which can be between 10-30nm thick, such as 15nm, 20nm, 25nm thick.
Next, as shown in S3 of fig. 1 and fig. 4, step S3 is performed to form an auxiliary functional structure 105 on the epitaxial structure, where the auxiliary functional structure 105 includes several stacked auxiliary unit layers, such as auxiliary unit layers 105a, 105b, and 105c, the auxiliary unit layers are p-type doped layers, and the doping concentration of each auxiliary doped layer of the auxiliary functional structure gradually increases from bottom to top. That is, in one example, the doping concentration of each auxiliary unit layer may be uniform doping, the doping concentration of 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 epitaxial process.
Specifically, the auxiliary functional 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 increased, holes start to be injected into the channel and generate an equal number of electrons, thereby increasing the 2 DEG. Electrons with high mobility will reach the drain under the influence of the electric field, while holes will remain, since their mobility is much lower than that of electrons. Thus, the current is modulated by the number of holes injected. And shows a double peak in the transconductance curve. Referring to fig. 9 and 10, fig. 9 shows simulation curves (transconductance curves) of a GaN device designed by using the multi-layer graded auxiliary function structure of the present invention, and fig. 10 shows simulation curves (transconductance curves) obtained by single-layer single doping as a comparison. Therefore, the two graphs respectively obtain double-peak curves, wherein the 2 nd is a gm peak value generated by injecting holes, the linearity of the device can be improved through the P-type doped auxiliary function structure, the holes can be injected step by adopting the scheme of multi-layer gradual change auxiliary function structure design, the gm planarization is more obvious, the fall between the 2 peak values is relieved, the gm planarization is further improved, and the linearity of the device is improved.
The auxiliary functional structure 105 includes, for example, 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, only the GaN functional structure, or both of them. Preferably, either one of the two is used.
In an example, the auxiliary functional structure 105 is only constituted by the AlGaN functional structure, in particular the AlGaN functional structure comprises several AlGaN unit layers as the auxiliary unit layers, such as the auxiliary unit layers 105a, 105b, 105 c.
In another example, the auxiliary functional structure 105 is composed of only the GaN functional structure, in particular, the GaN functional structure includes several GaN unit layers as the auxiliary unit layers, for example, the auxiliary unit layers 105a, 105b, 105 c.
In a further example, when the auxiliary functional structure 105 is selected as the AlGaN functional structure, the manufacturing method further includes a step of forming a GaN insertion layer (not shown in the figure) between the AlGaN functional structure and the barrier layer 104, and the GaN insertion layer is also removed when the auxiliary functional portion is formed. Specifically, the GaN insertion layer may serve as a selective etching stop layer, and the thickness may be between 1 nm and 5nm, for example, 2nm, 3nm, or 4nm may be designed. For example, a GaN layer is interposed between the AlGaN barrier and the p-AlGaN cap layer.
As an example, the number of the auxiliary unit layers is n, and is 1 st layer to nth layer from bottom to top, n is an integer greater than or equal to 2, for example, shown as 3 layers in fig. 4, and are: a first auxiliary unit layer 105a, a second auxiliary unit layer 105b, and a third auxiliary unit layer 105 c. The concentration of each auxiliary unit layer is increased linearly, so that the stability and repeatability of the process are improved.
In one example, each of the auxiliary unit layers has a doping concentration of (0.8-1.2) n 1018/cm3. That is, the doping concentration of each of the auxiliary unit layers may be 0.9n 1018/cm3、n*1018/cm3、1.1n*1018/cm3. Correspondingly, taking three auxiliary unit layers as an example, the doping concentration of each layer is: the first auxiliary unit layer 105a is 0.9 x 1018/cm3(ii) a The second auxiliary unit layer 105b was 1.8 x 1018/cm3(ii) a The third auxiliary unit layer 105c was 2.7 x 1018/cm3. The doping concentration of each layer is in another example: the first auxiliary unit layer 105a is 1 × 1018/cm3(ii) a The second auxiliary unit layer 105b is 2 x 1018/cm3(ii) a The third auxiliary unit layer 105c is 3 x 1018/cm3. The doping concentration of each layer is in yet another example: the first auxiliary unit layer 105a is 1.1 × 1018/cm3(ii) a The second auxiliary unit layer 105b was 2.2 x 1018/cm3(ii) a The third auxiliary unit layer 105c was 3.3 x 1018/cm3. And so on for the other layers.
In a further example, the auxiliary functional structure 105 has a total doping concentration between 1018/cm3-1019/cm3I.e. the sum of the doping concentrations in the individual auxiliary cell layers is between 1018/cm3-1019/cm3In between. For example, it may be 2 x 1018/cm3、5*1018/cm3、8*1018/cm3. In another alternative example, the auxiliary functional structure 105 has a total thickness of between 10nm and 100nm, for example, 20nm, 50nm, 60nm, 80 nm. The method is favorable for ensuring the grid control capability and relieving the short channel effect.
Next, as shown in S4 in fig. 1 and fig. 5-6, step S4 is performed to define a gate region on the surface of the auxiliary functional structure 105, and etch a portion of the auxiliary functional structure 105 around the gate region to the barrier layer 104, so as to obtain an auxiliary functional portion 107 corresponding to the gate region.
As an example, referring to fig. 7 and 8, the auxiliary function portion 107 may have a square shape in a longitudinal cross section, as shown in fig. 7, or a trapezoidal shape, as shown in fig. 8. In a preferred example, the longitudinal cross-sectional shape of the auxiliary function portion 107 is selected to be a trapezoid, and the transconductance curve simulation structure is shown in fig. 11, it can be seen that gm displayed by a transconductance curve obtained by the trapezoid auxiliary function portion is flatter, thereby being more beneficial to linear optimization. In addition, taking the auxiliary functional structure 105 having three auxiliary unit layers 105a, 105b, and 105c as an example, after the auxiliary functional part 107 is obtained by etching, the first auxiliary unit layer 105a is converted into a first functional part 107a, the second auxiliary unit layer 105b is converted into a second functional part 107b, and the third auxiliary unit layer 105c is converted into a third functional part 107 c.
In one example, the auxiliary function portion 107 may be formed by: as shown in fig. 5, a layer of ITO (Indium-Tin-Oxide) material is now deposited on the surface of the auxiliary functional structure 105, and the thickness may be between 100nm and 500nm, for example, 200nm and 300nm are selected; then, defining the gate region by using a photoetching process, and removing the redundant ITO material layer by using wet etching to form an ITO structure 106 which can be used as a gate metal layer and can be jointly used as a part of a subsequent gate electrode; next, as shown in fig. 6 and with reference to the structure of fig. 8, the ITO structure 106 is used as a mask to remove the excess material layer in the auxiliary functional structure 105, so as to obtain the auxiliary functional portion 107 for device modification. In this example, the ITO layer is compatible with GaN optoelectronic device processes and, as a transparent electrode, can be characterized with relevant optical methods. Moreover, the process limitation in subsequent source electrode and drain electrode preparation (such as Ni/Au preparation) is small, and the preparation efficiency and reliability of the device can be improved.
In another example, the auxiliary function portion 107 may be formed in such a manner that: the method comprises the steps of firstly defining a gate region by utilizing a photoetching mask, etching an auxiliary function structure, and preparing a source ohmic contact and a drain ohmic contact to obtain a source electrode and a drain electrode, and then depositing Ni/Au on the gate to obtain the gate electrode.
As an example, the auxiliary function portion 107 may be formed by etching: 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.
In an example, ICP etching is used to remove most of the p-doped AlGaN or GaN, for example, until the last auxiliary unit layer, such as the first auxiliary unit layer 105a, is left, or when the auxiliary functional structure is composed of several AlGaN layers and a GaN insertion layer is additionally provided, the GaN insertion layer is used. Further, etching (etching off the remaining GaN layer) to the barrier layer (e.g., AlGaN layer) is performed continuously by using a method of oxidation combined with wet etching.
In a specific example, the oxidation and wet etching may be performed by using O2 plasma or ozone O3 to form Ga — O, and then removing the oxide layer by using an acidic chemical, such as HCl, until reaching the surface of the barrier layer.
In addition, when the longitudinal cross-sectional shape of the auxiliary function portion 107 is a trapezoid, the auxiliary function portion 107 may be further optimally designed, for example, in one example, the auxiliary function portion 107 having a trapezoid shape is prepared by: a trapezoidal mask 203 is prepared on the auxiliary functional structure 105, and etching is performed based on the trapezoidal mask 203, so that the pattern of the trapezoidal mask 203 is transferred to the auxiliary functional structure 105, and a trapezoidal auxiliary functional portion 107 is obtained.
In one specific example, referring to fig. 12-14, a specific way to prepare the trapezoidal reticle 203 is provided:
first, as shown in fig. 12, a mask material layer 201 (a photolithographic resin) is formed on the auxiliary functional structure 105; the material of the mask material layer 201 may be PMMA, for example, the thickness thereof may be 500nm to 1 μm, and may be 600nm, 800 nm;
continuing to refer to fig. 12, performing exposure by using an electron beam exposure technique (E-beam), wherein the exposure dose gradually increases from the gate region (corresponding to the ITO structure in the figure) to both sides; for example, the exposure dose inside the gate region may be chosen to be the same. In one embodiment, the exposure dose is gradually increased from the center to the sides, e.g., from 300uc/cm2Increasing to 500uc/cm2In further examples, the exposure dose may increase linearly;
next, as shown in FIG. 13, the exposed structure is developed to obtain a stepped reticle 202, which may be a MIBK development;
finally, as shown in fig. 14, tempering the stepped mask 202 to obtain the trapezoidal mask 203; in one example, the process of tempering may be: annealing at 110-130 deg.C (such as 120 deg.C) for 1-10min (such as 2min, 5min) to form the desired smooth bevel edge mask, and obtaining the trapezoidal mask 203.
In another example, the manner of preparing the trapezoidal auxiliary functional portion 107 may also be to adopt electrochemical anisotropic etching, and utilize the characteristic that the higher the doping concentration is, the faster the etching rate is, to obtain the trapezoidal auxiliary functional portion, so as to simplify the process. For example, for the GaN auxiliary functional structure, an acid chemical reagent can be used, a sample is immersed in the reagent, and then bias voltage is applied through an electrode arranged in the reagent, so that electrochemical wet etching is performed.
Finally, as shown in S5 in fig. 1 and fig. 7-8, step S5 is performed to prepare a source electrode 108, a drain electrode 109, and a gate electrode 110 on the epitaxial structure, so as 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, and when the gate region is defined by using a photoresist mask, the gate electrode 110 is directly formed on the surface of the auxiliary function portion 107. In one specific example, the source and drain regions are defined by photolithography, metal is deposited, stripped to form the source and drain electrodes, and annealed at 800-900 deg.C (e.g., 850 deg.C) under N2 for 25-35 s (e.g., 30s) to complete the fabrication of ITO gate and source and drain electrodes. Of course, other processes may be used to prepare the individual device electrodes.
In one example, when the auxiliary function portion 107 having a trapezoidal cross section is obtained, the long side (the side in contact with the barrier layer) of the auxiliary function portion 107 having a trapezoidal cross section extends to be in contact with the two source electrodes and the two drain electrodes, that is, the trapezoidal structure has an edge in linear contact with the surfaces of the two electrodes in contact with the barrier layer, so as to facilitate the effective gradual hole injection.
As an example, the step of forming the source electrode 108, the drain electrode 109 and the gate electrode 110 further includes: and depositing a SiN layer by using a CVD process or depositing an Al2O3 layer by using an ALD process to serve as a device passivation layer so as to passivate the surface of the device. Of course, an Al2O3 layer may be formed first, and then an SiN layer may be formed on the surface of Al2O3 layer.
In addition, as shown in fig. 7 and 8, and referring to fig. 1 to 6 and fig. 9 to 11, the present invention further provides a GaN device structure, and the GaN device structure is preferably prepared by the preparation method of the present invention, and of course, may also be prepared by other methods, wherein the features in the GaN device structure may refer to the description in the preparation method of this embodiment, and are not described herein again.
The GaN device structure of this embodiment includes:
a substrate 101;
an epitaxial structure formed on the substrate and including at least a GaN channel layer 103 and a barrier layer 104 disposed from bottom to top;
the epitaxial structure comprises an auxiliary function part 107, a gate region is defined on the surface of the auxiliary function part, the auxiliary function part is formed on the epitaxial structure corresponding to the gate region, the auxiliary function structure comprises a plurality of superposed auxiliary unit layers which are p-type doped layers, and the doping concentration of the auxiliary doped layers is gradually increased from the lower layer to the upper layer;
and a source electrode 108, a drain electrode 109, and a gate electrode 110 formed on the epitaxial structure, the gate electrode corresponding to the gate region, the source electrode and the drain electrode being located at the periphery of the auxiliary function portion 107.
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 a plurality of AlGaN unit layers as the auxiliary unit layers; when the GaN functional layer is included, the GaN functional layer includes a plurality of GaN unit layers as the auxiliary unit layers.
As an example, the number of the auxiliary unit layers is n, and the auxiliary unit layers are respectively from 1 st layer to n th layer from bottom to top, n is an integer greater than or equal to 2, wherein the doping concentration of each auxiliary unit layer is (0.8-1.2) n 1018/cm3And the total doping concentration of the auxiliary functional structure is between 1018/cm3-1019/cm3And the total thickness is between 10nm and 100 nm.
As an example, the auxiliary function portion 107 has a trapezoidal longitudinal sectional shape.
In summary, according to the GaN device structure and the method for manufacturing the same of the present invention, by introducing the multiple layers of p-type doped and graded-concentration auxiliary functional portions, the auxiliary functional portions are simultaneously used as cap layer structures of the device, so that when the gate voltage is continuously increased, holes start to be injected into the channel and generate equal number of electrons, thereby increasing the 2 DEG. Electrons with high mobility will reach the drain under the action of the electric field, while holes will remain, since their mobility is much lower than that of electrons, so that the current is modulated by the number of holes injected, which can show a double peak in the transconductance curve, effectively improving the linearity of the device. In addition, the invention also introduces a trapezoidal design based on hole injection, and further improves the linearity of the device. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which may be made by those skilled in the art without departing from the spirit and scope of the present invention as defined in the appended claims.

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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