CN103730492B - MIS-HEMT device with back surface field plate structure and preparation method thereof - Google Patents

Abstract

The invention discloses a MIS-HEMT device with a back field plate structure and a preparation method thereof. The device can be fabricated by a common semiconductor device processing technology, which includes a source, a drain, a heterostructure and a back field plate electrode, the source and the drain are electrically connected by two-dimensional electrons formed in the heterostructure, and The source, the drain form an ohmic contact with the heterostructure, the heterostructure includes a first semiconductor layer and a second semiconductor layer arranged in sequence along a set direction, the first semiconductor layer is arranged between the source and the drain, and the first A gate is also provided on the surface of the semiconductor layer, and a first insulating dielectric layer is also provided between the gate and the first semiconductor layer to form an MIS structure. The back field plate electrode is arranged on a side of the second semiconductor layer far away from the first semiconductor layer. side surface. The invention can effectively improve the breakdown voltage of the device and suppress the "current collapse" effect to the greatest extent.

Description

MIS-HEMT device with back field plate structure and its preparation method

technical field

The invention relates to a MIS-HEMT (High Electron Mobility Transistor, high electron mobility transistor) device, in particular to a MIS-HEMT device with a back field plate structure and a preparation method thereof.

Background technique

Group III nitride semiconductor MIS-HEMT devices, due to piezoelectric polarization and spontaneous polarization effects, will form a two-dimensional electron gas with high concentration and high mobility at the heterojunction interface, such as the AlGaN/GaN interface. In addition, the HEMT device with group III nitride semiconductor as the substrate material can obtain a high breakdown voltage and a low specific on-resistance at the same time. Due to the large band gap of the material, it has high high temperature operating performance and good radiation resistance. Therefore, it is not only suitable for high-frequency power amplifier devices, but also applicable to the field of power electronics for high-power power switching devices.

When the existing Group III nitride semiconductor HEMT devices are used as high-frequency devices or high-voltage and high-power switching devices, there is a phenomenon of "current collapse". That is, when the device works in DC pulse mode or high-frequency mode, the output current of the drain 5 cannot keep up with the change of the control signal of the gate 7, and the current of the drain 5 decreases instantaneously and the turn-on delay increases. Seriously affect the practicability of the device. In the final analysis, this phenomenon is a storage effect of charge. The principle is that when the device works in the off state (off state), electrons will be trapped by the trap state, and the release of these trapped electrons is relatively slow, so when the gate voltage of the device is placed higher than the threshold voltage again, The on-state current of the device will be greatly reduced, and the turn-on delay will be larger. In order to avoid the "current collapse" effect of the device, surface passivation, surface treatment, or a field plate structure is often used on the front of the device to prevent the injection of electrons into the trap state in the semiconductor. Thereby slowing down the current collapse effect. However, these problems can only solve the "current collapse" when the device works at low voltage, because at low voltage, electrons only fill the trap states on the semiconductor surface, and when the device works at high voltage, electrons will be more inclined to In order to fill the deep-level trap states in the semiconductor body at the bottom, these deep-level trap states will be more difficult to release electrons than the surface trap states. The effect of "collapse" effect will be greatly reduced.

Contents of the invention

The main purpose of the present invention is to provide a MIS-HEMT device with a back field plate structure to overcome the deficiencies in the prior art.

In order to realize the above-mentioned purpose of the invention, the present invention has adopted following technical scheme:

A MIS-HEMT device with a back field plate structure, including a source, a drain, and a heterostructure, the source and the drain are electrically connected through two-dimensional electrons formed in the heterostructure, and the source The electrode and the drain form an ohmic contact with the heterostructure, the heterostructure includes a first semiconductor layer and a second semiconductor layer arranged in sequence along a set direction, the first semiconductor layer is arranged between the source and the drain, and A gate is also provided on the surface of the first semiconductor layer, and a first insulating dielectric layer is provided between the gate and the first semiconductor layer to form a MIS structure, and the MIS-HEMT device also includes a back field plate electrode, so The back field plate electrode is disposed on a surface of the second semiconductor layer that is far away from the first semiconductor layer.

As one of the more preferred implementations, the distance between the gate and the source is smaller than the distance between the gate and the drain.

As one of the feasible implementations, at least one edge of the back field plate electrode extends toward the source or the drain, and at the same time, the orthographic projection of the back field plate electrode overlaps with both edges of the gate.

Further, the back field plate electrode is electrically connected to the gate or the source to form a back gate field plate or a back source field plate.

Further, the source and the drain are respectively connected to the low potential and the high potential of the power supply.

As one of the feasible implementations, the edges on both sides of the back field plate electrode respectively extend toward the source and the drain.

Or, as one of the feasible implementations, only one edge of the back field plate electrode extends toward the source or the drain.

Further, when the MIS-HEMT device is working, the gate electrode and the back field plate electrode are respectively controlled by a control signal.

Further, the MIS-HEMT device also includes a support base, the support base includes a support substrate, and the support substrate is provided with a sub-source, a sub-drain and a sub-gate, and the sub-source, sub-drain The pole and the sub-gate are electrically connected to the source, the drain and the gate respectively.

As one of the more preferred implementations, an insertion layer for improving the mobility of the two-dimensional electron gas at the heterojunction interface may also be provided between the first semiconductor layer and the second semiconductor layer.

As one of specific implementations, the first semiconductor layer includes an AlGaN layer, and the second semiconductor layer includes a GaN layer.

As one of specific implementations, the insertion layer may include an AlN layer.

As one of the more optional implementations, a second insulating dielectric layer may also be provided between the back field plate electrode and the second semiconductor layer.

Further, the thickness of the second semiconductor layer is smaller than that of the corresponding second semiconductor layer in the existing MIS-HEMT device. Or, from another point of view, the thickness of the second semiconductor layer should be small enough, so that the back field plate electrode is close enough to the two-dimensional electron gas formed at the heterojunction interface, so that the two-dimensional electron gas can be effectively controlled. The areal density of the gas.

Moreover, the "existing MIS-HEMT device" mentioned here refers to the MIS-HEMT device which has the basic device structure shown in Figure 2 and which can be obtained through any known means before the filing date of the patent of the present invention.

Further, the supporting substrate is mainly formed of a material that is easy to conduct heat and not easy to conduct electricity.

Further, when the drain is connected to a high potential, the source is connected to a low potential, and the gate is connected to a potential lower than the threshold voltage, and the MIS-HEMT device is in an off state, the back field plate electrode is connected to a negative voltage; and when the The gate is connected to a potential higher than the threshold voltage, and when the MIS-HEMT device is in a conduction state, the back field plate electrode is connected to a high potential.

Another object of the present invention is to provide a kind of method for preparing this MIS-HEMT device with back field plate structure, it comprises the steps:

(1) Forming a heterostructure mainly composed of the first semiconductor layer and the second semiconductor layer on the selected substrate, the source and drain forming ohmic contacts with the heterostructure, and forming the heterostructure mainly composed of the first semiconductor layer The MIS structure formed by the first insulating dielectric layer and the gate on the surface, thereby obtaining the MIS-HEMT matrix structure;

(2) The selected substrate is removed, and a back field plate electrode is provided on the surface of the second semiconductor layer away from the first semiconductor layer.

As one of the preferred embodiments, step (2) further includes: after removing the selected substrate, performing thinning treatment on the second semiconductor layer, and then setting a back field plate electrode on the second semiconductor layer.

As one of the preferred implementations, step (2) further includes: removing the selected substrate, and forming a second insulating dielectric layer on the surface of the second semiconductor layer away from the first semiconductor layer, and then A back field plate electrode is arranged on the second insulating medium layer.

Both the aforementioned first insulating medium layer and the second insulating medium layer can be made of insulating materials known in the art.

Further, the method further includes: connecting the MIS-HEMT base structure with a support base mainly composed of a support substrate, and making the sub-source, sub-drain and sub-gate distributed on the support substrate respectively The source, the drain and the gate are electrically connected, and then the operation of removing the selected substrate is performed.

Further, the method for connecting the supporting base and the MIS-HEMT base structure includes flip-chip welding or wafer bonding technology.

Compared with the prior art, the present invention has at least the following advantages: by improving the structure of the existing MIS-HEMT device, including setting the back field plate electrode in the device structure, and using it with the gate to realize the two-dimensional The effective control of the electron gas and the redistribution of the electric field when the device is working enable the drain output current of the MIS-HEMT to keep up with the change of the gate voltage and suppress the "current Collapse effect", at the same time, the redistribution of the electric field can also play a role in increasing the breakdown voltage.

Description of drawings

Fig. 1 is a kind of sectional structure schematic diagram of the MIS-HEMT device with back field plate structure among the present invention;

Fig. 2 is a structural schematic diagram of an existing MIS-HEMT device;

FIG. 3 is one of the structural schematic diagrams of the MIS-HEMT device in Embodiment 1 of the present invention, wherein the back field plate extends toward the drain 5 and the source 6 respectively;

Fig. 4 is the second schematic diagram of the structure of the MIS-HEMT device in Embodiment 1 of the present invention, wherein the back field plate only extends toward the source electrode 6;

5 is the third schematic diagram of the structure of the MIS-HEMT device in Embodiment 1 of the present invention, wherein the back field plate only extends toward the drain 5 electrode;

6 is a schematic structural view of the MIS-HEMT device in Embodiment 2 of the present invention, wherein the back field plate electrode 10 is electrically connected to the gate 7;

FIG. 7 is a schematic structural view of the MIS-HEMT device in Embodiment 3 of the present invention, wherein the back field plate electrode 10 is electrically connected to the source 6;

Fig. 8 is a schematic structural view of a MIS-HEMT device with a back field plate structure in a typical embodiment of the present invention;

Fig. 9 is a flow chart of the manufacturing process of a MIS-HEMT device with a back field plate structure in a typical embodiment of the present invention.

detailed description

Referring to Figure 2, the reason for the current collapse phenomenon in existing MIS-HEMT devices (such as AlGaN/GaN devices) is that when a high voltage is applied to the drain 5 of the device and a voltage lower than the threshold is applied to the gate 7, the device will be turned off. Under the action of an electric field, the donor-like trap states in the high-field regions of the AlGaN surface 11 and the GaN body 12 will capture electrons and be negatively charged. Under the action of electrostatic induction, these negative charges will make the corresponding AlGaN/GaN The two-dimensional electron gas at the interface 13 decreases equally, and when the areal density of these trap states is high enough, the two-dimensional electron gas in the channel can even be completely depleted. It takes a certain amount of time for these electrons trapped in the trap to be released, and the shortest time is on the order of microseconds, or even on the order of seconds. When the device is turned on instantaneously, the amount of two-dimensional electron gas in the channel under the gate will be greatly increased under the induction of the gate voltage, but in the area where the gate 7 cannot be controlled, the two-dimensional electron gas in the channel is still controlled Because the total amount of negative charges trapped by the trap is still very small, the on-resistance of the device becomes larger, and it must wait until the trap state completely releases electrons to reach the proper amount. This kind of device has a turn-on delay and a larger on-resistance The phenomenon is "current collapse".

In order to solve the defects of the aforementioned common MIS-HEMT devices, the present invention proposes a MIS-HEMT device with a back field plate structure, the core structure of which is shown in Figure 1, wherein the supporting base plays the role of mechanical support and electrode extraction, When explaining the principle of the device, this part is omitted. The source 6 and the drain 5 of the device are located on one side of the first semiconductor layer 3 (such as AlGaN), and are arranged at both ends, and the gate 7 is also located on the side of the first semiconductor layer 3, and between the source 6 and the drain 5 In addition, the gate 7 is relatively close to the source 6. The back field plate electrode 10 is located on one side of the second semiconductor layer 2 (such as GaN), and since the second semiconductor layer 2 has been thinned, the back field plate electrode 10 is closer to the two-dimensional electron gas at the heterojunction interface, which can effectively Controlling the areal density of the two-dimensional electron gas. When the drain 5 of the device is connected to a high voltage, the source 6 is connected to 0 potential, and the gate 7 is connected to a potential lower than the threshold voltage, and the device is in the off state, the back field plate electrode 10 can apply a negative voltage, thereby inhibiting the first semiconductor layer 3 The trapping of electrons at the surface 11 and in the body 12 of the second semiconductor layer prevents the reduction of the two-dimensional electron gas at the heterojunction interface. When the potential higher than the threshold voltage is applied to the gate 7 of the device, and the device is in the on state, a high voltage is applied to the back field plate electrode 10, which can additionally induce a two-dimensional electron gas 14 at the heterojunction interface to make up for its loss , so as to suppress the reduction of on-resistance and reduce the turn-on delay, thereby solving the "current collapse" effect.

Referring again to FIG. 8, it is an AlGaN/GaN MIS-HEMT device in a typical embodiment of the present invention, which includes a source 6, a drain 5 and a gate 7, a back field plate electrode 10, and a supporting base. The insulating dielectric layer, the AlGaN/GaN heterostructure, and the two-dimensional electron gas located at the interface of the heterojunction, and the source and drain electrodes 5 are electrically connected through the two-dimensional electron gas. The source and drain electrodes 5 are located on one side of AlGaN and form ohmic contact with AlGaN. The gate 7 is located on the side of AlGaN and separated from AlGaN by an insulating dielectric layer 4 to form a MIS structure. The back field plate electrode 10 is located on the side of GaN and separated from GaN. Take another insulating dielectric layer 9 . The supporting base has a sub-source 6', a sub-drain 5', a sub-gate 7' and a supporting substrate 8. The back field plate electrode 10 has a wider coverage than the gate 7 .

The aforementioned sub-source 6', sub-drain 5', and sub-gate 7' can be combined with the source 6, drain 5, and gate 7 respectively by flip-chip welding or wafer bonding technology.

Furthermore, it should be noted that the aforementioned insulating dielectric layer disposed between the back field plate electrode and the second semiconductor layer can also be omitted.

Referring to Figure 9 again, the MIS-HEMT device can be prepared by the following process:

a) Complete the traditional AlGaN/GaN MIS-HEMT device structure on the substrate 1 material, that is, the MIS-HEMT device base;

b) On the supporting substrate 8, a supporting base including a sub-source 6', a sub-drain 5' and a sub-gate 7' is formed. The support substrate material can be any applicable material;

c) Combining the base of the MIS-HEMT device with the supporting base to form a combined body, which is characterized in that the substrate of the base of the MIS-HEMT device is on the top. The source 6, the drain 5, and the grid 7 are electrically connected to the sub-source 6', the sub-drain 5', and the sub-gate 7' respectively;

d) Using the existing semiconductor processing technology, the material of the substrate 1 of the combination is removed, and only the AlGaN/GaN epitaxial structure remains, and the GaN layer is on the top at this time.

e) Thinning the GaN layer to an appropriate thickness using existing thinning process means.

f) constructing a back field plate electrode 10 on the thinned GaN;

g) Interconnecting the back field plate electrode 10 with the source 6 or the gate 7 , or using the back field plate electrode 10 alone for applying electrical signals.

Of course, the technical solution of the present invention can also be applied to HEMT (HEMT), its structure includes: source, drain and heterostructure (such as AlGaN/GaN) and two-dimensional electron gas at the heterojunction interface, back field plate Electrode, supporting base. The source and the drain are located on one side of the AlGaN, form an ohmic contact with the AlGaN, and are electrically connected through the two-dimensional electrons formed in the heterostructure. The gate is located on one side of the AlGaN and forms a Schottky contact with the substrate. The HEMT device has a back field plate electrode and a supporting base, and the back field plate electrode is located on one side of the second semiconductor layer (such as GaN). The supporting base includes a sub-source, a sub-drain, and a sub-gate, which are respectively combined with the source, the drain, and the gate.

The technical solution of the present invention has been summarized above. In order to enable the public to understand the technical means of the present invention more clearly and implement it according to the contents of the specification, the technical solution of the present invention will be further described below.

Embodiment 1 Referring to FIG. 3, this MIS-HEMT has AlGaN/GaN. GaN is not intentionally doped. AlGaN can be doped with n-type impurities or not. The thickness of AlGaN is about 15 to 30 nm.

This MIS-HEMT has a drain 5 and a source 6 . The drain 5 and the source 6 form an ohmic contact with AlGaN/GaN, and form a good electrical connection with the two-dimensional electron gas in the channel. The drain 5 and the source 6 are ohmic contacts formed of multilayer metals (eg Ti/Al/Ti/Au or Ti/Al/Ni/Au, etc.) through rapid high-temperature annealing.

Further, the MIS-HEMT has a gate 7, between the source 6 and the drain 5, the distance close to the source 6 is relatively short, the gate 7 is located on a dielectric layer 4, and the dielectric layer 4 is located on the AlGaN above. The dielectric layer 4 can be made of Al ₂ O ₃ and the like, and can be deposited on the AlGaN by means of PECVD, ALD and other techniques.

The back field plate electrode 10 is located on the GaN, overlaps the gate 7 in the vertical direction, and extends toward the source and drain 5 directions (or only extends toward the drain 5 or source 6, see Fig. 4 shows that the back field plate electrode 10 only extends toward the drain 5).

The supporting substrate 8 supporting the base can be an AlN substrate with a thickness of 100~1000um, and the sub-source 6', sub-drain 5', and sub-gate 7' can all be made of Ti (50~100)/Au (50~ 1000nm) metal layer.

The working principle of the MIS-HEMT with a back field plate is as follows: when a potential higher than the threshold voltage is applied to the gate 7, the two-dimensional electron gas concentration in the channel is high, and the device is in an on state; At the potential of the threshold voltage, the two-dimensional electron gas in the channel is exhausted, and the device is in an off state; by controlling the potential on the gate 7, the concentration of the two-dimensional electron gas in the channel corresponding to the gate 7 can be controlled, Thereby controlling the switching state of the device channel.

Independent electrical signal control can be applied to the back field plate electrode 10 (the same potential as the grid 7 or source 6 can also be applied, as shown in Figure 6, the back field plate electrode 10 is electrically connected to the grid 7 to realize An example with the same potential as the gate 7), and the concentration of the two-dimensional electron gas 14 in the corresponding channel can be controlled by applying different electrical signals to the back field plate electrode 10 .

Embodiment 2 Referring to FIG. 6, this MIS-HEMT has AlGaN/GaN. GaN is not intentionally doped. AlGaN can be doped with n-type impurities or not. The thickness of AlGaN is about 15 to 30 nm.

This MIS-HEMT has a drain 5 and a source 6 . The drain 5 and the source 6 form an ohmic contact with AlGaN/GaN, and form a good electrical connection with the two-dimensional electron gas in the channel. The drain 5 and the source 6 are ohmic contacts formed of multilayer metals (eg Ti/Al/Ti/Au or Ti/Al/Ni/Au, etc.) through rapid high-temperature annealing.

Further, the MIS-HEMT has a gate 7, between the source 6 and the drain 5, the distance close to the source 6 is relatively short, the gate 7 is located on a dielectric layer 4, and the dielectric layer 4 is located on the AlGaN above. The dielectric layer 4 can be made of Al ₂ O ₃ and the like, and can be deposited on the AlGaN by means of PECVD, ALD and other techniques.

The back field plate electrode 10 is located on the GaN, overlaps the gate 7 in the vertical direction, and extends toward the source and drain 5 directions (or only extends toward the drain 5 or source 6, see Fig. 4 shows that the back field plate electrode 10 only extends toward the drain 5).

The supporting substrate 8 supporting the base can be an AlN substrate with a thickness of 100~1000um, and the sub-source 6', sub-drain 5', and sub-gate 7' can all be made of Ti (50~100)/Au (50~ 1000nm) metal layer.

The working principle of the MIS-HEMT with a back field plate is as follows: when a potential higher than the threshold voltage is applied to the gate 7, the two-dimensional electron gas concentration in the channel is high, and the device is in an on state; At the potential of the threshold voltage, the two-dimensional electron gas in the channel is exhausted, and the device is in an off state; by controlling the potential on the gate 7, the concentration of the two-dimensional electron gas in the channel corresponding to the gate 7 can be controlled, Thereby controlling the switching state of the device channel.

The back field plate electrode 10 applies a control signal at the same potential as the gate 7 to control the concentration of the two-dimensional electron gas 14 in the corresponding channel.

Embodiment 3 Referring to FIG. 7, this MIS-HEMT has AlGaN/GaN. GaN is not intentionally doped. AlGaN can be doped with n-type impurities or not. The thickness of AlGaN is about 15 to 30 nm.

This MIS-HEMT has a drain 5 and a source 6 . The drain 5 and the source 6 form an ohmic contact with AlGaN/GaN, and form a good electrical connection with the two-dimensional electron gas in the channel. The drain 5 and the source 6 are ohmic contacts formed of multilayer metals (eg Ti/Al/Ti/Au or Ti/Al/Ni/Au, etc.) through rapid high-temperature annealing.

Further, the MIS-HEMT has a gate 7, between the source 6 and the drain 5, the distance close to the source 6 is relatively short, the gate 7 is located on a dielectric layer 4, and the dielectric layer 4 is located on the AlGaN above. The dielectric layer 4 can be made of Al ₂ O ₃ and the like, and can be deposited on the AlGaN by means of PECVD, ALD and other techniques.

The back field plate electrode 10 is located on the GaN, overlaps the gate 7 in the vertical direction, and extends toward the source and drain 5 directions (or only extends toward the drain 5 or source 6, see Fig. 4 shows that the back field plate electrode 10 only extends toward the source 6).

The supporting substrate 8 supporting the base can be an AlN substrate with a thickness of 100~1000um, and the sub-source 6', sub-drain 5', and sub-gate 7' can all be made of Ti (50~100)/Au (50~ 1000nm) metal layer.

The working principle of the MIS-HEMT with a back field plate is as follows: when a potential higher than the threshold voltage is applied to the gate 7, the two-dimensional electron gas concentration in the channel is high, and the device is in an on state; At the potential of the threshold voltage, the two-dimensional electron gas in the channel is exhausted, and the device is in an off state; by controlling the potential on the gate 7, the concentration of the two-dimensional electron gas in the channel corresponding to the gate 7 can be controlled, Thereby controlling the switching state of the device channel.

The back field plate electrode 10 applies a control signal at the same potential as the source electrode 6 to control the concentration of the two-dimensional electron gas 14 in the corresponding channel.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Those of ordinary skill in the art should understand that they can still modify the technical solutions described in the previous solutions, or modify the technical solutions of the present invention. Some of the technical features are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the spirit and scope of the device solution of the present invention.

Claims (11)

1. A MIS-HEMT device with a back field plate structure, comprising a source (6), a drain (5) and a heterostructure, the source (6) and the drain (5) being formed on the heterostructure The two-dimensional electrons in the structure are gas-electrically connected, and the source (6) and drain (5) form an ohmic contact with the heterostructure, and the heterostructure includes first semiconductor layers ( 3) and the second semiconductor layer (2), the first semiconductor layer (3) is arranged between the source (6) and the drain (5), and the surface of the first semiconductor layer (3) is also provided with a gate (7 ), a first insulating dielectric layer (4) is also provided between the gate (7) and the first semiconductor layer (3) to form a MIS structure, and it is characterized in that it also includes a back field plate electrode (10), The back field plate electrode (10) is arranged on a side surface of the second semiconductor layer (2) away from the first semiconductor layer (3), and the back field plate electrode (10) is connected to the second semiconductor layer ( 2) There is also an insulating dielectric layer distributed between them, wherein the second semiconductor layer (2) has been thinned. 2. the MIS-HEMT device with back field plate structure according to claim 1, is characterized in that, at least one side edge of said back field plate electrode (10) is toward source (6) or drain (5) direction extending, and at the same time, the orthographic projection of the back field plate electrode (10) overlaps the edges on both sides of the grid (7). 3. the MIS-HEMT device with back field plate structure according to claim 1, is characterized in that, described back field plate electrode (10) is electrically connected with gate (7) or source (6) and forms back gate field plate or back source field plate. 4. The MIS-HEMT device with a back field plate structure according to claim 1, characterized in that the source (6) and the drain (5) are respectively connected to the low potential and the high potential of the power supply. 5. according to the described MIS-HEMT device with back field plate structure of claim 1 and 2, it is characterized in that, the both sides edge of described back field plate electrode (10) is respectively to source (6) and drain (5) ) direction, or only one edge of the back field plate electrode (10) extends toward the source (6) or drain (5) direction. 6. the MIS-HEMT device with back field plate structure according to claim 1, is characterized in that, when described MIS-HEMT device works, described gate (7) and back field plate electrode (10) are made of respectively A control signal control. 7. The MIS-HEMT device with the back field plate structure according to claim 1, is characterized in that it also includes a support base, the support base includes a support substrate (8), on the support substrate (8) There are sub-source (6'), sub-drain (5') and sub-gate (7'), and the sub-source (6'), sub-drain (5') and sub-gate (7' ) are electrically connected to the source (6), drain (5) and gate (7) respectively. 8. The MIS-HEMT device with a back field plate structure according to claim 1, characterized in that, the first semiconductor layer (3) comprises an AlGaN layer, and the second semiconductor layer (2) comprises a GaN layer. 9. according to claim 1 or 8 described MIS-HEMT device with back field plate structure, it is characterized in that, the thickness of described second semiconductor layer (2) is less than that of corresponding second semiconductor layer in existing MIS-HEMT device thickness. 10. A method for preparing an MIS-HEMT device with a back field plate structure, characterized in that it comprises the following steps: (1) forming a semiconductor layer mainly composed of the first semiconductor layer (3) and the second semiconductor layer (3) on the selected substrate (1). A heterostructure composed of two semiconductor layers (2), a source (6) and a drain (5) forming ohmic contact with the heterostructure, and a first insulating medium mainly formed on the surface of the first semiconductor layer (3) layer (4) and the MIS structure formed by the gate (7), thereby obtaining the MIS-HEMT base structure; (2) removing the selected substrate (1), and thinning the second semiconductor layer (2) After processing, an insulating medium layer is set on the surface of the second semiconductor layer (2) away from the first semiconductor layer (3), and then a back field plate electrode (10) is set on the insulating medium layer. 11. according to the preparation method of the MIS-HEMT device with back field plate structure described in claim 10, it is characterized in that, it also comprises: this MIS-HEMT matrix structure and the support base that mainly is made up of support substrate (8) connected, and the sub-source (6'), sub-drain (5') and sub-gate (7') distributed on the support substrate (8) are respectively connected to the source (6), drain (5) is electrically connected to the gate (7), and then the operation of removing the selected substrate (1) is performed.