CN106098749A - AlGaN/GaN heterojunction structure and growing method thereof on a kind of silicon substrate - Google Patents

Abstract

The invention discloses AlGaN/GaN heterojunction structure and growing method on a kind of silicon substrate, pass first into ammonia and Si (111) substrate is carried out surfaces nitrided process；Growing AIN nucleating layer the most on a si substrate；The AlxGa1 xN cushion of growth Al component stairway degression and AlN/GaN superlattices are as combined strain-buffer layer；Growth GaN channel layer, AlGaN potential barrier and GaN cap the most successively.The present invention is by regulating the growth technique of AlN nucleating layer and introducing AlxGa1 xN intermediate layer and AlN GaN superlattice structure as combined strain-buffer layer, can effectively control the stress in epitaxial film, reduce the threading dislocation density in epitaxial layer of gallium nitride simultaneously, obtain the high-quality AlGaN/GaN heterogenous junction epitaxy material of flawless on Si substrate, low warpage.

Description

AlGaN/GaN heterostructure on silicon substrate and its growth method

technical field

The invention relates to the field of semiconductor material growth, in particular to an AlGaN/GaN heterostructure on a silicon substrate and a growth method.

Background technique

As a third-generation semiconductor, GaN material has many advantages such as large band gap, strong critical breakdown field, high thermal conductivity, high saturation drift velocity, and good chemical and thermodynamic stability. In particular, because of the strong polarization effect, the AlGaN/GaN heterostructure can generate a two-dimensional electron gas with a concentration of about 1013cm-2. The high electron mobility transistor based on this structure has high current density, critical strike The breakthrough voltage and electron mobility make it have very important application value in the field of microwave power and high temperature electronic devices.

Due to the lack of available GaN single crystal substrates, currently GaN materials are mainly obtained by heteroepitaxial growth on SiC, sapphire and Si substrates. However, due to the high hardness, poor electrical conductivity and thermal conductivity of sapphire, it brings a lot of inconvenience to the processing and application of later devices. SiC also has the disadvantages of high hardness and high cost. , good thermal and electrical conductivity, and mature device processing technology make Si-based GaN devices have unparalleled cost advantages in large-scale production and application of other substrate materials. GaN thin film epitaxial growth technology on Si substrates and related Mechanism research has also been widely concerned by scholars and industries at home and abroad.

However, it is very difficult to achieve high-quality epitaxial growth of GaN thin films on Si substrates. First, Si in the substrate will react with reaction chamber residues and group III and V elements. Metal Ga will react with Si at high temperature. The substrate undergoes a melting back etching reaction, and at the same time, the Si atoms in the substrate will also diffuse to the buffer layer, resulting in regional surface defects and damage in the epitaxial layer; in addition, there is a very serious crystallization gap between GaN and the substrate. Lattice constant mismatch (17%) and thermal mismatch (56%) will introduce a large number of dislocations and tensile stress in the epitaxial layer, especially during the cooling process at the end of growth, the accumulation of tensile stress will be further formed, resulting in epitaxial The deformation and warping of the wafer will cause cracks in the epitaxial film in severe cases, and the warping and film cracking of the epitaxial wafer will become more and more serious with the increase of the size of the epitaxial substrate and the thickness of the epitaxial film.

The epitaxial growth of Si-based GaN films needs to reduce the influence of lattice mismatch and thermal mismatch between Si and GaN as much as possible. Commonly used methods include AlN nucleation layer, AlGaN and superlattice structure stress buffer intermediate layer, etc. technology. However, even with these methods, in order to obtain high-quality GaN thin films on Si substrates, there are still problems in the combination of growth process conditions and epitaxial structures.

Contents of the invention

Purpose of the invention: In view of the above-mentioned defects in the prior art, the present invention aims to provide an AlGaN/GaN heterogeneous structure and growth method on a silicon substrate, improve the crystal quality of the GaN epitaxial layer and alleviate the mismatch stress, and avoid the epitaxial thin film surface The generation of cracks suppresses the deformation and warpage of epitaxial wafers.

Technical solution: An AlGaN/GaN heterostructure on a silicon substrate, which includes an AlN nucleation layer, an AlxGa1-xN buffer layer, an AlN/GaN superlattice buffer layer, and a GaN channel from bottom to top on a silicon substrate layer, AlGaN barrier layer and GaN capping layer.

Further, the thickness of the AlN nucleation layer is 100-250 nm.

Further, the thickness of the AlxGa1-xN buffer layer is 300-1200 nm, the Al composition of the AlxGa1-xN buffer layer changes gradually from bottom to top, and the value of X is 0.7-0.3.

Further, the GaN channel layer has a thickness of 0.5-1.5 μm.

A method for growing an AlGaN/GaN heterostructure on a silicon substrate, in which an AlN nucleation layer, an AlxGa1-xN buffer layer, an AlN/GaN superlattice buffer layer, and a GaN channel are sequentially grown on a silicon substrate from bottom to top layer, AlGaN barrier layer and GaN capping layer.

Further, before the AlN nucleation layer is grown, ammonia gas is introduced into the reaction chamber to carry out nitriding treatment on the surface of the silicon substrate, wherein the flow rate of ammonia gas for nitriding treatment is 5-10 L/min, and the temperature is 850-950°C , The duration of nitriding treatment is 10-20s.

Further, the thickness of the AlN nucleation layer is 100-250nm, the molar ratio of ammonia gas to trimethylaluminum in the reaction chamber is 2000-4000 during growth, and the growth temperature is 950-1050°C.

Further, the thickness of the AlxGa1-xN buffer layer is 300-1200nm, the growth temperature is 1000-1100°C, wherein the Al molar composition of the AlxGa1-xN buffer layer changes gradually from bottom to top, and the value of X is 0.7-0.3 .

Further, the growth temperature of the AlN/GaN superlattice buffer layer is 1000-1100° C., and the growth cycle is 10-100. In each cycle, the thickness of AlN is 3-6 nm, and the thickness of GaN is 18-28 nm.

Further, the growth temperature of the GaN channel layer is 1000-1100° C., and the thickness is 0.5-1.5 μm.

Beneficial effects: the present invention provides an AlGaN/GaN heterostructure and growth method on a silicon substrate, which can avoid the remelting etching reaction between the Si substrate and Ga, fully relieve the mismatch stress in the epitaxial layer and reduce the penetration potential. Dislocation density, thereby effectively improving the surface morphology and crystal quality of AlGaN/GaN heterojunction materials, high electron mobility transistors based on this material structure have high electron mobility and two-dimensional electron gas concentration, and have material uniformity And the advantages of good repeatability of the growth process.

Description of drawings

FIG. 1 is a schematic diagram of an epitaxial growth structure of an AlGaN/GaN heterojunction on a silicon substrate in the present invention.

Fig. 2 is an atomic force microscope (AFM) image of the surface of an AlGaN/GaN heterojunction on a silicon substrate in the present invention.

Fig. 3 is the stress test result of the warpage of the AlGaN/GaN heterojunction epitaxial wafer on the silicon substrate in the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1:

As shown in Figure 1, an AlGaN/GaN heterostructure on a silicon substrate includes an AlN nucleation layer, an AlxGa1-xN buffer layer, an AlN/GaN superlattice buffer layer, GaN channel layer, AlGaN barrier layer and GaN capping layer.

The positional relationships such as "upper" and "lower" in the present invention are based on the relative positional relationship shown in the drawings, which are only for the convenience of description, rather than indicating or implying that the referred part must have a specific orientation, so it cannot be understood as Limitations on the Invention.

Among them, the thickness of the AlN nucleation layer is 100-250nm, the thickness of the AlxGa1-xN buffer layer is 300-1200nm, the Al composition of the AlxGa1-xN buffer layer changes gradually from bottom to top, the value of X is 0.7-0.3, and the GaN The thickness of the channel layer is 0.5-1.5 μm, the thickness of the AlGaN barrier layer is 20-30 nm, the Al component is 20%-30%, and the thickness of the GaN capping layer is 2-3 nm.

The growth method of AlGaN/GaN heterostructure on a silicon substrate is to grow an AlN nucleation layer, an AlxGa1-xN buffer layer, an AlN/GaN superlattice buffer layer, and a GaN channel layer sequentially from bottom to top on a silicon substrate , AlGaN barrier layer and GaN capping layer, the MOCVD (metal organic chemical vapor deposition) method is taken as an example below, which specifically includes the following steps:

(1) Put the Si(111) substrate 1 in the MOCVD reaction chamber, and perform high-temperature baking treatment under the hydrogen atmosphere, and the treatment temperature is 1050°C.

(2) The temperature of nitriding treatment is 850-950°C. In this embodiment, the temperature of the reaction chamber is lowered to 950°C, and ammonia gas is introduced to carry out nitriding treatment on the surface of the silicon substrate 1, wherein the flow rate of ammonia gas is 5-10L /min, the time of nitriding treatment is 10-20s, its function is to form a layer of amorphous SiNx layer with a thickness of 2-3nm on the surface of the silicon substrate, which can prevent the diffusion of Si in the substrate to the upper layer, thereby avoiding GaN During the growth, Si and Ga undergo melting back etching reaction.

(3) Keeping the temperature constant, grow the AlN nucleation layer 2. The thickness of the AlN nucleation layer 2 is 100-250nm. In this embodiment, the growth thickness of the AlN nucleation layer 2 is selected to be between 150-200nm. The molar ratio of gas to trimethylaluminum (ie V/III ratio) is 2000-4000.

(4) Keeping the temperature constant, the thickness of the AlxGa1-xN buffer layer is 300-1200 nm. In this embodiment, an AlXGa1-XN buffer layer 3 with a thickness of 1 μm and a gradual change in Al composition is selected to be grown on the high-temperature AlN nucleation layer 2. Component X gradually changes from 0.7 to 0.3 from bottom to top, and the function of this layer is to provide lattice transition and relieve mismatch stress.

(5) AlN/GaN superlattice buffer layer 4 is grown on the AlXGa1-XN buffer layer 3, the growth thickness of AlN and GaN for each superlattice period is 3-6nm and 18-28nm respectively, and the growth period is 10-100 In this embodiment, the growth thicknesses of AlN and GaN are selected to be 5nm and 20nm respectively, and the growth cycles are 50 cycles. The function of this layer is to block threading dislocations and provide stress control.

(6) A GaN channel layer 5 with a thickness of 0.5-1.5 μm is grown on the AlN/GaN superlattice buffer layer 4 , and the thickness of the GaN channel layer 5 in this embodiment is 1 μm.

(7) An AlGaN barrier layer 6 with an Al composition of 25% is grown on the GaN channel layer 5 with a thickness of 25 nm.

(8) A GaN capping layer 7 is grown on the AlGaN barrier layer 6 with a growth thickness of 2 nm.

As shown in Figure 2, the surface morphology of the AlGaN/GaN heterojunction epitaxial material was characterized by an atomic force microscope. The surface atomic steps are clearly visible, and the root mean square roughness is 0.31nm.

As shown in Figure 3, the deformation and warpage of the Si-based AlGaN/GaN heterojunction epitaxial wafer was measured by a stress tester, and the bow and warp values representing the curvature of the wafer were -23 μm and 30 μm, respectively, indicating that the growth through this example The stress control of the epitaxial wafer is better.

Example 2:

This embodiment also provides an AlGaN/GaN heterostructure on a silicon substrate and its growth method, its structure and method are roughly the same as those described in Embodiment 1, the difference between the two is that in step (2) the The temperature of the reaction chamber is reduced to 850° C., the thickness of the AlN nucleation layer 2 described in the step (3) is 100 nm, the thickness of the AlxGa1-xN buffer layer described in the step (4) is 300 nm, and each step described in the step (5) The growth thickness of AlN and GaN of superlattice period is 3nm and 18nm respectively, grows 100 periods, the thickness of GaN channel layer 5 described in step (6) is 0.5 μm, and the AlGaN barrier described in step (7) The growth thickness of the layer 6 is 20nm, the Al composition is 20%, and the growth thickness of the GaN capping layer 7 in the step (8) is 2.5nm.

Example 3:

This embodiment also provides an AlGaN/GaN heterostructure on a silicon substrate and its growth method, its structure and method are roughly the same as those described in Embodiment 1, the difference between the two is that in step (2) the The temperature of the reaction chamber is reduced to 900° C., the thickness of the AlN nucleation layer 2 described in the step (3) is 250 nm, the thickness of the AlxGa1-xN buffer layer described in the step (4) is 1200 nm, and each step described in the step (5) The growth thickness of AlN and GaN of a superlattice period is 6nm and 28nm respectively, grows 10 periods, the thickness of the GaN channel layer 5 described in the step (6) is 1.5 μm, and the AlGaN barrier described in the step (7) The growth thickness of the layer 6 is 30nm, the Al composition is 30%, and the growth thickness of the GaN capping layer 7 in step (8) is 3nm.

The foregoing embodiments have specifically described and demonstrated the technical methods and implementation effects of the present invention. For those skilled in the art, after understanding the content and principles of the present invention, they can Next, various amendments and changes in form and details are made according to the method of the present invention, but these amendments and changes based on the present invention are still within the protection scope of the claims of the present invention.

Claims (10)

1. AlGaN/GaN heterojunction structure on a silicon substrate, it is characterised in that include the most successively on silicon substrate (1) AlN nucleating layer (2), AlxGa1-xN cushion (3), AlN/GaN super-lattice buffer layer (4), GaN channel layer (5), AlGaN potential barrier Layer (6) and GaN cap (7).

AlGaN/GaN heterojunction structure on a kind of silicon substrate the most according to claim 1, it is characterised in that described AlN nucleation The thickness of layer (2) is 100～250nm.

AlGaN/GaN heterojunction structure on a kind of silicon substrate the most according to claim 1, it is characterised in that described AlxGa1- The thickness of xN cushion (3) is 300～1200nm, and the Al component of described AlxGa1-xN cushion (3) is successively decreased change from bottom to top Changing, the value of X is 0.7～0.3.

AlGaN/GaN heterojunction structure on a kind of silicon substrate the most according to claim 1, it is characterised in that described GaN raceway groove The thickness of layer (5) is 0.5～1.5 μm.

5. the growing method of AlGaN/GaN heterojunction structure on a silicon substrate, it is characterised in that on silicon substrate (1) from lower and On growing AIN nucleating layer (2), AlxGa1-xN cushion (3), AlN/GaN super-lattice buffer layer (4), GaN channel layer successively (5), AlGaN potential barrier (6) and GaN cap (7).

The growing method of AlGaN/GaN heterojunction structure on a kind of silicon substrate the most according to claim 5, it is characterised in that In the forward direction reative cell of growing AIN nucleating layer (2), it is passed through ammonia, surface of silicon is carried out nitrogen treatment, wherein at nitridation The ammonia flow velocity of reason is 5～10L/min, and temperature is 850～950 DEG C, and the nitrogen treatment persistent period is 10～20s.

The growing method of AlGaN/GaN heterojunction structure on a kind of silicon substrate the most according to claim 5, it is characterised in that The thickness of described AlN nucleating layer (2) is 100～250nm, and during growth, in reative cell, the mol ratio of ammonia and trimethyl aluminium is 2000 ～4000, growth temperature is 950～1050 DEG C.

The growing method of AlGaN/GaN heterojunction structure on a kind of silicon substrate the most according to claim 5, it is characterised in that The thickness of described AlxGa1-xN cushion (3) is 300～1200nm, and growth temperature is 1000～1100 DEG C, wherein AlxGa1- The Al molar constituent of xN cushion (3) is successively decreased change from bottom to top, and the value of X is 0.7～0.3.

The growing method of AlGaN/GaN heterojunction structure on a kind of silicon substrate the most according to claim 5, it is characterised in that The growth temperature of described AlN/GaN super-lattice buffer layer (4) is 1000～1100 DEG C, grows 10～100 cycles, each cycle The thickness of middle AlN is 3～6nm, and the thickness of GaN is 18～28nm.

The growing method of AlGaN/GaN heterojunction structure on a kind of silicon substrate the most according to claim 5, it is characterised in that The growth temperature of described GaN channel layer (5) is 1000～1100 DEG C, and thickness is 0.5～1.5 μm.