A sputtering growth method of sandwiched deposition of AlN thin film

Abstract

The application discloses a sputtering growth method for sandwich deposition of AlN film, characterized in that a layer of AlN film A is first grown on a substrate by using a homoepitaxial target material with a slow growth speed, and then a layer of AlN film B is grown by using a heteroepitaxial target material with a fast growth speed, and the process is repeated to obtain the sandwich deposition of AlN film. The sandwich deposition of AlN film obtained by using the method has a smooth surface and a fast growth speed, and can be well compatible with a mass production and low cost preparation process. Meanwhile, the sandwich deposition of AlN film obtained by using the method is beneficial to release of recrystallization stress in subsequent high-temperature annealing, and can realize an AlN crystal film with low stress.

Description

TECHNICAL FIELD

[0001] The present application relates to a sputtering growth method for sandwich deposition of AlN thin film, belonging to the technical field of semiconductor materials. BACKGROUND

[0002] Aluminum nitride (AlN) is a III-V compound semiconductor with a wurtzite crystal structure. It is considered as one of the most promising materials for high frequency, high voltage, deep ultraviolet semiconductor devices and high power electronic device heat dissipation layer due to its high band gap, high ultrasonic speed, very large piezoelectric coupling coefficient, high thermal conductivity and high breakdown voltage. In many applications of AlN thin film, the performance of the device is closely related to the crystal orientation, crystal microstructure, surface morphology and other material properties of the AlN thin film. Controlling and optimizing these properties on material growth is an important topic for the application of AlN thin film.

[0003] AlN thin film has been synthesized by several methods, such as chemical vapor deposition, pulsed laser ablation deposition, molecular beam epitaxy, electron spray method and ion beam deposition, etc. In addition, such as reactive radio frequency (RF) magnetron sputtering, reactive medium frequency (MF) magnetron sputtering, reactive pulsed direct current (DC) unbalanced magnetron sputtering, etc. have been used to prepare AlN thin film. Most of the methods can be applied to preferentially grow c-axis oriented AlN thin film on different substrates under appropriate deposition conditions. Among them, various magnetron sputtering has become the first choice for preparing AlN thin film due to its low deposition temperature, easy to obtain source material and relatively simple process steps, further considering the need to integrate the technology with integrated circuit manufacturing technology at the end of the cost is lower. In the early research, some researchers discussed the influence of substrate temperature on the crystalline grain properties of AlN thin film. Such as the influence of deposition temperature on the crystal grain orientation of AlN thin film, the influence of pure nitrogen atmosphere and sputtering pressure on the grain size and deposition rate of AlN thin film, etc.

[0004] In previous studies, highly c-axis oriented AlN films have been obtained at different substrate temperatures, and many sputtering rules have been understood, and some technical constraints have also been found. For example, in order to obtain a relatively flat AlN film surface, a relatively low deposition rate is usually required, which is generally about 1-2 nm / min. If a higher deposition rate is used, the film surface will be rougher. In addition, under the condition of low cost, such as using a metal Al target for sputtering growth, the growth rate is usually fast, reaching about 20 nm / min, which is difficult to reduce. On the other hand, since the AlN film prepared by sputtering is a polycrystalline structure, subsequent high-temperature annealing is required to recrystallize the grains into a relatively complete crystal film. During this recrystallization process, the grains will rearrange and form internal stress. If the initial state of the overall AlN film is the same structure everywhere, synchronous recrystallization everywhere will accumulate stress, resulting in film cracking or wafer warping. Conversely, if the AlN film internal recrystallization is not synchronized, the recrystallization stress can be released or compensated. Therefore, in the sputtering growth technology of AlN film, a sputtering growth method is needed that can use a faster growth rate, obtain a flat surface, and eliminate the recrystallization stress problem caused by subsequent high-temperature annealing.

[0005] It should be noted that although the manufacture of different grain layers during growth is beneficial to stress regulation and surface morphology regulation, the most common method to obtain different grains is to change the growth rate of AlN by changing the growth conditions such as temperature, power, gas, gas pressure, etc. This process requires precise regulation of the chemical reaction changes caused by the change of growth conditions, and the chemical reaction process is very sensitive to the growth conditions, which ultimately leads to difficulty in controlling the consistency, repeatability and controllability of growth. Correspondingly, when a growth process starts with homogeneous AlN and forms grains mainly through physical processes, there is no need for chemical reactions during grain growth, and the volatility of grain growth is greatly reduced. SUMMARY

[0006] The purpose of the present application is to provide a sputtering growth method for realizing sandwich deposition of AlN film by combining different target materials, and to improve the surface flatness of AlN film and provide stress release or compensation for subsequent high-temperature annealing by forming a combination of different grain layers in the film.

[0007] The purpose of the present application is achieved by the following technical solutions:

[0008] A sputtering growth method for realizing sandwich deposition of AlN film by combining different target materials, in which a layer of AlN film A is first grown on the substrate using a homogeneous target material with a slow growth rate, and then a layer of AlN film B is grown using a heterogeneous target material with a fast growth rate, and the process is repeated to obtain a sandwich deposition of AlN film.

[0009] The slow growth rate homogenous target material refers to an AlN target material, and the fast growth rate heterogeneous target material refers to an Al target material.

[0010] Preferably, the thickness of the AlN film A layer is in the range of 10-100 nm, and the grain equivalent diameter of the layer is in the range of 5-50 nm.

[0011] Preferably, the growth conditions of the AlN film A layer are as follows:

[0012] Sputtering power: 20-100 W;

[0013] N2 gas flow rate: 0-100 sccm;

[0014] Ar gas flow rate: 0-100 sccm;

[0015] Chamber gas pressure: 3-20 mTorr;

[0016] Substrate temperature: room temperature-500°C.

[0017] Preferably, the thickness of the AlN film B layer is in the range of 100-500 nm, and the grain equivalent diameter of the layer is in the range of 100-300 nm.

[0018] Preferably, the growth conditions of the AlN film B layer are as follows:

[0019] Sputtering power: 100-300 W;

[0020] N2 gas flow rate: 0-100 sccm;

[0021] Ar gas flow rate: 0-100 sccm;

[0022] Chamber gas pressure: 3-20 mTorr;

[0023] Substrate temperature: room temperature-500°C.

[0024] Preferably, the number of cycles of growth of the A layer and the B layer is in the range of 1-100, and one cycle of growth of one A layer and one B layer is referred to as one cycle.

[0025] Preferably, the substrate is a sapphire substrate or a silicon substrate.

[0026] The interlayer-deposited AlN film is prepared by the above-mentioned sputtering growth method for interlayer-deposited AlN film.

[0027] When sputtering is performed using an AlN target, since AlN powder is already on the AlN target, the chemical property is relatively stable, the target material is relatively dense, the active source concentration is not high, the formation of AlN grains is mainly physical process, small grains are formed, the AlN thin film with small grains has a relatively flat surface, and the deposition speed of the AlN thin film on the substrate is slow.

[0028] When sputtering is performed using a metal Al target, since Al is on the Al target, the chemical property is active, the active source is easily sputtered, the substrate is heated to a high temperature, the atomic migration and chemical reaction on the surface of the substrate are accelerated, the Al-N chemical reaction on the surface needs to be grown, larger grains can be grown, the AlN thin film with larger grains has a relatively rough surface, and the deposition speed of the AlN thin film on the substrate is fast. Moreover, when AlN grains are formed on the surface of a heterogeneous material, due to the difference in free energy on the surface of different materials, AlN tends to grow in an island shape, and as a result, a growth surface with larger surface undulations is formed.

[0029] The present application combines the characteristics of the two kinds of targets, and uses the two kinds of targets in combination to realize an AlN thin film with a sandwich structure having different grain sizes. In the present application, the A layer provides an AlN crystal surface, and is relatively flat. The B layer is grown on the A layer, and is different from crystallization on a heterogeneous material, the difference in free energy on the surface of the A layer is greatly reduced, at this time, the formation of AlN grains is more uniform, and a flat surface is beneficial to be formed. At the same time, due to the fast growth speed of the Al target, the method of the present application also maintains a relatively fast overall growth speed.

[0030] On the other hand, the AlN thin film prepared by sputtering is a polycrystalline structure, and usually needs to be further annealed at a high temperature to form a crystal thin film. During the high-temperature annealing process, it is obvious that there is a difference in the recrystallization process between the A layer and the B layer, and more grain boundaries in the A layer can become a channel for stress release or compensation of the B layer recrystallization. Therefore, asynchronous A layer recrystallization and B layer recrystallization can reduce the overall stress of the AlN crystal thin film after high-temperature annealing. Therefore, the sandwich AlN thin film structure obtained by growth in the present application is also beneficial to the subsequent high-temperature annealing process.

[0031] Advantages of the present application:

[0032] 1. The sandwich AlN thin film obtained by the method of the present application can simultaneously obtain an AlN thin film with a flat surface by using the different growth mechanisms of the homogeneous target and the heterogeneous target, and has a fast growth speed, and can be well compatible with a large batch low-cost preparation process.

[0033] 2. The sandwich AlN thin film obtained by the method of the present application is beneficial to release the recrystallization stress in the subsequent high-temperature annealing, and can realize an AlN crystal thin film with low stress. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a structural schematic diagram of the sandwich deposited AlN film obtained by the sputtering growth method of the present application.

[0035] Figure 2 is an AFM image of the surface of the first layer A layer prepared in Example 1.

[0036] Figure 3 is an AFM image of the surface of the second layer B layer with sandwich prepared in Example 1.

[0037] Figure 4 is an AFM image of the surface of the single layer B layer directly prepared in Comparative Example 1. DETAILED DESCRIPTION

[0038] The following clearly and completely describes the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0039] Example 1

[0040] The present embodiment provides a sputtering growth method for sandwich deposited AlN film, and atomic force microscope (AFM) is used to observe and analyze the surface morphology of the sample. The method comprises the following steps:

[0041] Step one: the sapphire substrate is sequentially placed in beakers containing acetone, ethanol and deionized water for ultrasonic cleaning, and then dried by air gun and placed in a sample box for standby; the ultrasonic cleaning temperature is preferably room temperature; the ultrasonic cleaning time is preferably 15 min; and the drying is preferably nitrogen blowing.

[0042] Step two: growing the first layer A layer

[0043] The first layer A layer is sputtered and grown by using AlN target material. The preferred sputtering growth conditions are as follows:

[0044] Sputtering power: 60 W;

[0045] N2 gas flow rate: 40 sccm;

[0046] Ar gas flow rate: 40 sccm;

[0047] Chamber pressure: 5 mTorr;

[0048] Substrate temperature: 100℃.

[0049] Under this condition, the growth rate of AlN film is slow, generally 100 nm / h. The thickness of A layer is 10-100 nm, preferably 25 nm.

[0050] The growth rate of A layer is slow, and the formed crystal grains are small. The surface structure of A layer is measured by atomic force microscope (AFM) as shown in Figure 2 which shows dense crystal grains with a diameter of about 20 nm, and the maximum surface fluctuation is 15 nm.

[0051] Step three: growing the second layer B layer

[0052] The second layer B layer is grown by sputtering with an Al target. Here, the target is directly converted for growth. The preferred sputtering growth conditions are as follows:

[0053] Sputtering power: 250 W;

[0054] N2gas flow rate: 60 sccm;

[0055] Ar gas flow rate: 20 sccm;

[0056] Chamber pressure: 5 mTorr;

[0057] Substrate temperature: 400°C.

[0058] Under this condition, the growth rate of AlN film is fast, generally 20 nm / min. The thickness of B layer is 100-500 nm, preferably 300 nm.

[0059] The growth rate of B layer is fast, and the film thickness can be increased to more than 300 nm in 15 minutes.

[0060] Step four: after cooling, the sample is taken out.

[0061] The structure of the grown interlayer deposited AlN film is shown in Figure 1 The AFM photo of the AlN film surface obtained by the above steps is shown in Figure 3 The maximum surface fluctuation is 10 nm. For comparison, a sample without step two is also prepared, which is Comparative Example 1, and the surface AFM photo is shown in Figure 4 The maximum surface fluctuation is 50 nm. Obviously, the surface of the A+B interlayer sample prepared in Example 1 is smoother, and there are no obvious separated crystal grains on the surface, and a continuous AlN film with a smooth surface has been formed. The surface AFM photo of the B layer directly prepared in Comparative Example 1 shows many separated large crystal grains, and the surface fluctuation is large.

[0062] The growth of A layer in step two and B layer in step three can be continued alternatively until the AlN film of desired thickness is obtained. Generally, the thickness of AlN film applied is not more than 10 μm.

[0063] Comparative Example 1

[0064] Compared with Example 1, the process in steps one and three is the same, and step two is skipped.

[0065] Step one: the sapphire substrate is sequentially placed in beakers containing acetone, ethanol and deionized water for ultrasonic cleaning, and then dried with air gun and placed in a sample box for standby; the temperature of ultrasonic cleaning is preferably room temperature; the time of ultrasonic cleaning is preferably 15 min; the drying is preferably nitrogen blowing.

[0066] Step two: directly grow B layer, use Al target for sputtering growth, and directly switch the target for growth. The preferred sputtering growth conditions are as follows:

[0067] Sputtering power: 250 W;

[0068] N2gas flow: 60 sccm;

[0069] Ar gas flow: 20 sccm;

[0070] Chamber pressure: 5 mTorr;

[0071] Substrate temperature: 400°C.

[0072] Under this condition, the growth rate of AlN film is fast, generally 20 nm / min. The thickness of B layer is 100 nm to 500 nm, preferably 300 nm.

[0073] The growth rate of B layer is fast, and the formed crystal grains are large. The surface structure is measured by AFM as shown in Figure 4 , which shows dense crystal grains with a diameter of about 150 nm, and the maximum surface fluctuation reaches 50 nm.

Claims

1. A sputter growth method of sandwich depositing an AlN thin film, characterized by A layer of AlN film A is first grown on a substrate using a homo-target with a slow growth rate, and then a layer of AlN film B is grown using a hetero-target with a fast growth rate, and the process is repeated to obtain a sandwiched deposition AlN film; wherein the homo-target with a slow growth rate refers to an AlN target, and the hetero-target with a fast growth rate refers to an Al target; The conditions for growing the AlN film A layer are as follows: Sputtering power: 20-100 W; N2 flow rate: 0-100 sccm; Ar flow rate: 0-100 sccm; Chamber pressure: 3-20 mTorr; Substrate temperature: room temperature-500°C; The conditions for growing the AlN film B layer are as follows: Sputtering power: 100-300 W; N2 flow rate: 0-100 sccm; Ar flow rate: 0-100 sccm; Chamber pressure: 3-20 mTorr; Substrate temperature: room temperature-500°C.

2. The method of claim 1, wherein the sputter-deposited AlN film is a sandwiched film. The thickness of the AlN film A layer ranges from 10 to 100 nm, and the grain equivalent diameter of this layer is 5-50 nm.

3. The method of claim 1, wherein the sputter-deposited AlN film is a sandwiched film. The thickness of the AlN film B layer ranges from 100 to 500 nm, and the grain equivalent diameter of this layer is 100-300 nm.

4. The sputter growth method of sandwiched deposition of AlN thin films according to any one of claims 1 to 3, characterized in that: The number of times of repeating the growth of the A layer and the B layer is 1-100.

5. The method of claim 4, wherein the sputter-deposited AlN film is a sandwiched film. The substrate is a sapphire substrate or a silicon substrate.

6. A sandwiched deposition AlN film prepared by the sputtering growth method of claim 1-5.

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