CN109065438B - Preparation method of AlN thin film - Google Patents

Abstract

A preparation method of an AlN thin film comprises the following steps: step 1: annealing the substrate for epitaxy; step 2: growing a first AlN layer on the substrate, wherein the growth temperature is the same as the annealing temperature in the step 1; and step 3: growing a second AlN layer on the first AlN layer, wherein the growth temperature and the Al source flow of the second AlN layer are gradually changed; and 4, step 4: and growing a third AlN layer with constant temperature and constant source on the second AlN layer. The method has simple process, and can realize the preparation of the low-dislocation AlN epitaxial material with high stability and high repeatability.

Description

Preparation method of AlN thin film

technical field

The invention relates to the technical field of semiconductor epitaxial growth, in particular to a preparation method for preparing high-quality AlN thin films by metal-organic chemical vapor deposition.

Background technique

The AlN semiconductor material has a band gap of 6.2eV, which belongs to the third generation of wide band gap semiconductor materials. It has the advantages of high breakdown voltage, high electron saturation speed, stable corrosion resistance, etc., and has strong spontaneous and piezoelectric polarity. Surface acoustic wave velocity, can form AlGaN alloy to realize continuous change of band gap, and prepare heterojunction device structure. Therefore, aluminum nitride-based wide bandgap materials are widely favored in the research field of cutting-edge optoelectronics and microelectronic devices due to their excellent semiconductor properties. Semiconductor materials, and with the wide application of third-generation semiconductor devices and chips, the demand for AlN-based high-aluminum nitride semiconductor materials will continue to grow.

At present, the quality of AlN materials is still difficult to meet the high-performance requirements of devices. The main reason is that due to the lack of high-quality and large-scale homogenous substrates, heterosubstrates such as sapphire are mainly used for epitaxy. Due to the huge lattice mismatch and Thermal mismatch, resulting in a large number of defects such as dislocations. Second, AlN itself requires harsh conditions for the epitaxial growth process. Due to the poor mobility of Al atoms on the epitaxial surface and the strong pre-reaction of the reaction source, various defects are easily formed during the nucleation and growth process of AlN. Therefore, the existing AlN epitaxy technology process generally focuses on substrate processing, medium and low temperature nucleation and high temperature growth. However, the direct high-temperature rapid growth on the medium-low temperature nucleation layer or the secondary epitaxial layer will be unfavorable for alleviating the strain, reducing the threading dislocation density, and even generating new dislocation sources. High-temperature AlN growth, or secondary epitaxy on a sputtered AlN or epitaxial AlN thick layer substrate, requires a suitable transitional growth process in the middle to further reduce stress and reduce defect density.

SUMMARY OF THE INVENTION

The technical problem solved by the present invention is to overcome the deficiencies of the prior art and provide a preparation method for preparing a high-quality AlN thin film, specifically a transitional epitaxy technology from substrate transition to high temperature AlN growth.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

The present invention provides a preparation method of AlN film, comprising the following steps:

Step 1: Anneal the substrate for epitaxy;

Step 2: grow the first AlN layer on the substrate, and the growth temperature is the same as the annealing temperature of step 1;

Step 3: growing a second AlN layer on the first AlN layer, the growth temperature of the second AlN layer and the Al source flow rate are graded;

Step 4: A third AlN layer of constant temperature and constant source is grown on the second AlN layer.

The above-mentioned technical scheme of the present invention has the following advantages and beneficial effects: by using this method, the substrate undergoes a suitable transition treatment and transition layer growth process to further reduce stress, reduce the defect density of high temperature AlN, and make the surface smooth. Compared with the existing general method, under the condition of other growth process conditions and the same thickness, the AlN epitaxial film obtained by this method has a significant improvement in the XRD scan (102) half-width at half maximum, which is reduced by 100-200 arcsec, (002 ) is also improved in width at half maximum, indicating a reduction in the density of screw and edge dislocations in the epitaxial film. The method is simple in process, and can realize the preparation of low-dislocation AlN epitaxial materials with high stability and high repeatability.

Description of drawings

In order to make the objects, technical solutions and advantages of the present invention clearer, the following detailed description is as follows in conjunction with the embodiments and the accompanying drawings, wherein:

Fig. 1 shows the step block diagram of the preparation method of a kind of AlN thin film provided by the present invention;

FIG. 2 shows a schematic diagram of the structure of AlN grown by this method in Example 1 of the present invention.

specific embodiment

The preparation method of an AlN film provided by the present invention is a preparation process for growing the AlN film by metal organic chemical vapor deposition (MOCVD ₎ , and the reaction source adopts hydride NH gas and organic metal Al source, such as TMAl and TEAl, etc. Epitaxial growth is carried out in a MOCVD reaction chamber at a certain temperature, pressure and atmosphere. Referring to Figure 1, the present invention provides a method for preparing an AlN film, comprising the following steps:

Step 1: annealing the substrate 10 for epitaxy at high temperature, the temperature for annealing the substrate 10 is 950-1150° C., the annealing time is 5-15 minutes, the annealing atmosphere is NH ₃ , H ₂ atmosphere, NH ₃ as protective gas. The substrate 10 includes, but is not limited to, an AlN bulk single crystal substrate; or a magnetron sputtered AlN on a sapphire, silicon carbide or silicon substrate or an AlN buffer layer grown in-situ; or AlN, GaN or gallium oxide, etc. Epitaxial layer template; high temperature annealing of the substrate can make the grains of the medium and low temperature buffer layer merge and grow to an appropriate degree and reduce the dislocation density. For secondary epitaxy, high temperature annealing can make the surface clean, and the atomic steps on the surface are flat and clear, which promotes the crystal quality of secondary epitaxy.

Step 2: After the high temperature annealing, a first AlN layer 11 is grown on the substrate 10. The growth temperature is the same as the high temperature annealing temperature in step 1. The thickness of the first AlN layer 11 is 5-30 nm; The growth temperature of the subsequent material is lower than that of the subsequent high temperature growth, so that there is a relatively low temperature AlN doped layer compared with the subsequent high temperature growth, which is beneficial to block dislocations and relieve the stress of the substrate.

Step 3: growing a second AlN layer 12 on the first AlN layer 11, the growth temperature of the second AlN layer 12 and the flow rate of the Al source are gradually changed, and the temperature variation range when the second AlN layer 12 is grown is: From the temperature of growing the first AlN layer 11 to the temperature of growing the third AlN layer 13 ; the variation range of the Al source flow is: from the Al source flow of the first AlN layer 11 to the Al when the third AlN layer 13 is grown source flow, the thickness of the second AlN layer 12 is 10-100nm; the innovative feature of this layer is that the growth temperature is gradually changed from low temperature to high temperature, and the reaction source V/III is gradually changed from high to low (the NH ₃ source is unchanged). , the organic Al source is gradually increased), and the growth temperature is gradually increased, which is conducive to the transformation of AlN growth from surface roughening to flattening. The reaction source V/III changes from high to low, and the diffusion length of Al atoms on the growth surface can be gradually adjusted, so that the growth from quasi-3D with shorter diffusion length tends to quasi-2D growth with longer diffusion length. The superposition of the two effects of temperature gradient and reaction source gradient will effectively bend and annihilate dislocations, so that dislocations cut off and penetrate upwards, thereby reducing the dislocation density of the subsequent upward epitaxial layers, and also conducive to the gradual release of stress.

Step 4: A third AlN layer 13 of constant temperature and constant source is grown on the second AlN layer 12, and the growth temperature of the third AlN layer 13 is 1000-1500°C. At high temperature, the surface migration ability of Al atoms is strong, and rapid two-dimensional growth can be achieved, and AlN epitaxial layer materials with low dislocation density, no cracks and smooth surface can be obtained.

The NH ₃ gas flow rate and the carrier gas amount of the reaction source during the growth of the first AlN layer 11 , the second AlN layer 12 and the third AlN layer 13 remain unchanged. Maintaining the stability of the airflow in the reaction chamber is conducive to maintaining the stability of the concentration field and the temperature field, improving the uniformity of the material and reducing the defect density.

The reaction pressure during the growth of the first AlN layer 11 , the second AlN layer 12 and the third AlN layer 13 remains unchanged. The range is 30-100torr, and the lower growth pressure is beneficial to reduce the parasitic reaction of the source and improve the crystal quality.

The preparation method described therein is to use metal organic chemical vapor deposition, ie, MOCVD epitaxial growth.

Wherein the steps 1-4 are continuous growth, and there is no transition or pause layer in the process between the steps.

Wherein the steps 1-4 can be cyclically grown in multiple cycles.

The present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

Example 1:

as shown in picture 2:

(1) Sputtering 75nm AlN on the (0001) plane sapphire substrate is used as the substrate 10; the sputtered AlN substrate 10 is heated to 1100° C. in the MOCVD reaction chamber, annealed at high temperature, and the gas atmosphere is NH ₃ and H ₂ atmosphere, Annealing time 5 minutes.

(2) Keeping the temperature at 1100° C., the pressure at 50 tort, and the flow rate of NH ₃ unchanged, the V/III ratio is 1280, and the TMAl source is fed to grow the first AlN layer 11 with a thickness of 15 nm.

(3) The temperature was increased from 1100 °C to 1250 °C, and the temperature was gradually increased, and the heating time was 5 minutes; at the same time, the carrier gas volume of the reaction source remained unchanged, the pressure remained unchanged at 50torr, and the flow rate of NH ₃ remained unchanged. Increase the flow rate of the TMAl source, by V/ The III ratio is gradually reduced from 1280 to 640, and a second AlN layer 12 is grown with a thickness of 50 nm.

(4) Under the condition that the temperature is kept at 1250° C. and the pressure is kept at 50 torr, the growth rate is 600 nm/h for 1 h to obtain the third AlN layer 13 .

The AlN epitaxial layer obtained in this example, observed under the atomic force microscope AFM, has a flat surface, the root mean square roughness is less than 1 nm, and two-dimensional step growth can be observed. The full width at half maximum of the curve is lower than 200arscec, and the half width of the (102) plane is lower than 650arscec. Compared with AlN without this method, that is, directly grown at elevated temperature on the sputtered AlN substrate, the (102) full width at half maximum is significantly different. The improvement is reduced by 100-200 arcsec, and the (002) full width at half maximum is also improved. Using this method, the density of screw and edge dislocations in the high temperature epitaxial AlN layer is significantly reduced. At a thickness of about 600 nm, high crystal quality and a smooth and flat surface are obtained.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in further detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (9)

1. a preparation method of AlN film, comprises the following steps: Step 1: Anneal the substrate for epitaxy; Step 2: grow the first AlN layer on the substrate, and the growth temperature is the same as the annealing temperature of step 1; Step 3: growing a second AlN layer on the first AlN layer, the growth temperature of the second AlN layer and the Al source flow rate are graded, and the growth temperature of the second AlN layer is gradually increased from the growth temperature of the first AlN layer To the temperature of the third AlN layer, the Al source flux of the second AlN layer is gradually increased from the Al source flux of the first AlN layer to the Al source flux of the third AlN layer; Step 4: A third AlN layer of constant temperature and constant source is grown on the second AlN layer. 2. The preparation method of the AlN thin film according to claim 1, wherein in the step 1, the substrate is annealed, the annealing temperature is 950-1150 ° C, the annealing time is 5-15 minutes, and the annealing atmosphere is NH ₃ and _H2 atmosphere. 3. The preparation method of the AlN thin film according to claim 1, wherein the thickness of the first AlN layer is 5-30 nm. 4. The method for preparing an AlN thin film according to claim 1, wherein the thickness of the second AlN layer is 10-100 nm. 5 . The preparation method of the AlN thin film according to claim 1 , wherein the growth temperature of the third AlN layer is 1000-1500° C. 6 . 6 . The preparation method of the AlN thin film according to claim 1 , wherein the NH ₃ gas flow rate and the carrier gas amount of the reaction source when the first AlN layer, the second AlN layer and the third AlN layer are grown remain unchanged. 7 . 7 . The method for preparing an AlN thin film according to claim 6 , wherein the reaction pressure during the growth of the first AlN layer, the second AlN layer and the third AlN layer remains unchanged. 8 . 8. The preparation method of AlN thin film according to claim 1, wherein said base comprises AlN bulk single crystal substrate; or AlN or in-situ grown by magnetron sputtering on sapphire, silicon carbide or silicon substrate AlN buffer layer; or AlN, GaN or gallium oxide epitaxial layer template. 9 . The preparation method of the AlN thin film according to claim 1 , wherein the preparation method adopts metal organic chemical vapor deposition (MOCVD) epitaxial growth. 10 .

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