CN103474331A - Method for growing epitaxy AlN template on sapphire substrate - Google Patents

Abstract

A method for growing an AlN template for epitaxy on a sapphire substrate, the scheme of which is: using trimethylaluminum as an MO source and _NH3 as a gaseous source, and growing an AlN template on the sapphire surface by a metal-organic chemical vapor deposition process; When growing the AlN template, trimethylaluminum is passed into the reaction chamber before _NH3 , and _NH3 is delayed for 1-5 seconds after the introduction of trimethylaluminum, after _NH3 reacts with the Al atoms attached to the sapphire surface AlN is generated, and finally an AlN template is grown on the surface of sapphire; the V/III ratio of NH ₃ and trimethylaluminum is 51~256, the pressure in the reaction chamber is 20~50mbar, and the temperature is 1200°C. The beneficial technical effects of the present invention are: the method is simple and practical, does not require a buffer layer, and can grow an atomic-level smooth AlN template at a relatively low substrate temperature (1200°C), and the average roughness of the AlN template is 0.5nm about.

Description

Method for growing AlN template for epitaxy on sapphire substrate

technical field

The present invention relates to an organic chemical vapor deposition (MOCVD) process, in particular to a method for growing an AlN template for epitaxy on a sapphire substrate.

Background technique

At present, the nitride epitaxial growth technology based on sapphire/GaN is very mature at home and abroad, but for deep ultraviolet optoelectronic devices, the luminous efficiency of the device will be seriously reduced due to the strong absorption of GaN materials on ultraviolet light. The incident light will be absorbed by the GaN layer and cannot enter the active region to generate photocurrent. Therefore, the nitride template based on sapphire/GaN is not suitable for making deep ultraviolet optoelectronic devices; in order to solve the above problems, a more feasible technology The route is: discard the GaN template, and directly grow an AlGaN epitaxial layer with a high Al composition on a sapphire substrate that has good transmission properties for deep ultraviolet light.

To grow AlGaN epitaxial layer with high Al composition, the most ideal substrate should be AlN, AlN crystal is transparent to ultraviolet light with a wavelength greater than 200nm, and AlN and AlGaN can form a good lattice match, and AlN also has relatively Good thermal conductivity (thermal conductivity 3Wcm ^-1 K ^-1 ) is beneficial to improve the high power performance of the device. In addition, due to the highest sound velocity (6200m/s) and high piezoelectric coupling coefficient among all known surface acoustic wave materials, AlN is also an ideal radio frequency surface acoustic wave material; however, currently The preparation technology of outer AlN single crystal substrate is immature, the price is expensive, and the supply is difficult (especially for large-scale substrates).

In 2006, Soukhoveev V et al. reported that the HVPE (Hydride Vapor Phase Epitaxy) method was used to successfully grow high-quality AlN templates on sapphire substrates, but the AlN templates obtained by the HVPE method could not be grown in situ. The epitaxial structure of the device, so the process is relatively complicated. From the perspective of reducing the complexity of the process, it is necessary to explore the technology of directly growing AlN template on the sapphire substrate by MOCVD method.

Contents of the invention

Aiming at the problems in the background technology, _the present invention proposes a method for growing an AlN template for epitaxy on a sapphire substrate. Phase deposition process grows AlN template on the surface of sapphire; when growing AlN template, trimethylaluminum is passed into the reaction chamber before NH ₃ , and after passing through trimethylaluminum, NH ₃ , NH ₃ After reacting with Al atoms attached to the surface of sapphire, AlN is generated, and finally AlN templates are grown on the surface of sapphire; the V/III ratio of _NH3 and trimethylaluminum is 51~256, the pressure in the reaction chamber is 20~50mbar, and the temperature is 1200°C.

The principle of the present invention is: the present invention adopts the method of passing through trimethylaluminum first and then passing through NH ₃ to grow the AlN template, and passing through trimethylaluminum in advance can make a layer of Al atoms pre-attached on the surface of the sapphire to avoid The direct contact of NH ₃ with the sapphire surface causes the sapphire surface to be nitrided, so as to effectively suppress the generation of AlN film with mixed polar domains and improve the uniformity of AlN growth rate. The present invention uses a low Ⅴ/Ⅲ ratio to grow the AlN template. The growth process in the prior art generally uses a high Ⅴ/Ⅲ ratio of 700 to 800. A high Ⅴ/Ⅲ ratio will lead to a decrease in the mobility of Al atoms on the substrate surface. It is not conducive to the establishment of a two-dimensional growth mode, and it is also not conducive to the formation of a smooth epitaxial surface. The reaction chamber air pressure of the process of the present invention is relatively low, and the low reaction chamber air pressure can effectively reduce NH ₃ and the reaction rate of trimethylaluminum in the gas phase, thereby reducing the generation of dust particles due to the reaction of NH ₃ and trimethylaluminum in the gas phase. Deposited on the substrate, at the same time, under the combined effect of low reaction chamber pressure and low V/III ratio, the mobility of Al atoms on the substrate can be further improved.

Preferably, the trimethylaluminum flow rate is 40-80 sccm, and the NH3 flow rate is 80-200 sccm.

Preferably, before growing the AlN template, the sapphire surface is cleaned of impurities at a temperature of 1200-1250° C., a pressure of 90-110 mbar, and a carrier gas flow rate of 5000-7000 sccm.

Preferably, the thickness of the AlN template is 1 μm. The thickness of the AlN template can be adjusted by controlling the reaction time. If the thickness of the AlN template is large, cracks are prone to occur.

The beneficial technical effects of the present invention are: the method is simple and practical, does not require a buffer layer, and can grow an atomic-level smooth AlN template at a relatively low substrate temperature (1200°C), and the average roughness of the AlN template is 0.5nm about.

Detailed ways

A method for growing an AlN template for epitaxy on a sapphire substrate, the innovation of which is: using trimethylaluminum as the MO source and _NH3 as the gaseous source, the AlN template is grown on the sapphire surface by a metal-organic chemical vapor deposition process; When growing the AlN template, trimethylaluminum is passed into the reaction chamber before _NH3 , and _NH3 is delayed for 1-5 seconds after the introduction of trimethylaluminum, after _NH3 reacts with the Al atoms attached to the sapphire surface AlN is generated, and finally an AlN template is grown on the surface of sapphire; the V/III ratio of NH ₃ and trimethylaluminum is 51~256, the pressure in the reaction chamber is 20~50mbar, and the temperature is 1200°C.

Further, the trimethylaluminum flow rate is 40-80 sccm, and the NH3 flow rate is 80-200 sccm.

Further, before growing the AlN template, the sapphire surface is cleaned of impurities at a temperature of 1200-1250° C., a pressure of 90-110 mbar, and a carrier gas flow rate of 5000-7000 sccm.

Further, the thickness of the AlN template is 1 μm.

Example:

Load the sapphire substrate into the reaction chamber of the MOCVD equipment, and bake it for 10 minutes in an environment with a substrate temperature of 1200°C, a hydrogen pressure of 100 mbar, and a carrier gas flow rate of 6000 sccm to eliminate surface impurities; adjust the pressure in the reaction chamber to 40 mbar. The bottom temperature is adjusted to 1200°C, and trimethylaluminum is introduced into the reaction chamber. The flow rate of trimethylaluminum is 60 sccm. After a delay of 3 seconds, NH ₃ is introduced into the reaction chamber. By controlling the reaction time, the sapphire surface grows a thickness of 1 μm AlN template.

Claims (4)

1. a method that adopts the AlN template outside Grown on Sapphire Substrates, is characterized in that: take trimethyl aluminium as MO source, NH ₃for gaseous source, adopt the metal organic-matter chemical vapor deposition process to grow the AlN template at sapphire surface; When the growing AIN template, trimethyl aluminium is prior to NH ₃pass in reative cell, pass into after trimethyl aluminium and postpone 1-5 and pass into again NH second ₃, NH ₃with the Al atom that the is attached to sapphire surface rear generation AlN that reacts, finally at sapphire surface, grow the AlN template; NH ₃with trimethyl aluminium V/the III ratio is 51 ~ 256, the reative cell internal gas pressure is 20 ~ 50mbar, temperature is 1200 ℃.

2. the method that adopts the AlN template outside Grown on Sapphire Substrates according to claim 1, it is characterized in that: the trimethyl aluminium flow is 40 ~ 80sccm, the NH3 flow is 80 ~ 200sccm.

3. the method that adopts the AlN template outside Grown on Sapphire Substrates according to claim 1, it is characterized in that: before the growing AIN template, be that 1200 ~ 1250 ℃, pressure are under 90 ~ 110mbar, the carrier gas flux condition that is 5000 ~ 7000sccm in temperature, sapphire surface is carried out to removal of impurities.

4. the method that adopts the AlN template outside Grown on Sapphire Substrates according to claim 1, it is characterized in that: described AlN template thickness is 1 μ m.