WO2023159829A1

WO2023159829A1 - In-situ laser interference photolithography method based on molecular beam epitaxy

Info

Publication number: WO2023159829A1
Application number: PCT/CN2022/101012
Authority: WO
Inventors: 石震武; 杨新宁; 彭长四; 缪力力; 庄思怡; 耿彪; 祁秋月
Original assignee: 苏州大学
Priority date: 2022-02-24
Filing date: 2022-06-24
Publication date: 2023-08-31
Also published as: CN114654097A; CN114654097B

Abstract

An in-situ laser interference photolithography method based on molecular beam epitaxy. The method comprises the following steps: S1: heating a substrate, wherein the substrate is made of a Ga-based or Al-based material, and the heating temperature is higher than a thermal desorption temperature of an In-based material corresponding to the material of the substrate; and S2: introducing an In atom flow to serve as a surface catalyst, and introducing laser interference to expose the substrate, thereby completing photolithographic processing. Structured photolithography on a material is realized in situ in a molecular beam epitaxy system by using traditional laser interference. In comparison with other existing non-in-situ material micro-nano processing means, there is neither pollution nor oxidation, the material damage is low, and the process is extremely simple and efficient. In addition, the etching precision of the material at an atomic level in a Z direction can be realized.

Description

In situ laser interference lithography based on molecular beam epitaxy

technical field

The invention belongs to the field of semiconductors, and in particular relates to an in-situ laser interference photolithography method based on molecular beam epitaxy.

Background technique

Various devices based on III-V compound semiconductor materials have been widely used in the fields of detectors, LEDs, lasers, solar cells, and RF communications. And all device development and manufacturing are inseparable from two links: one is material growth; the other is material processing. The equipment used for material growth mainly includes, for example, molecular beam epitaxy equipment and metal-organic vapor deposition equipment. The main use of material processing is the process of optical lithography, which is currently the most widely used in the industry. The manufacture of the micro-nano structure of the entire material generally goes through (but not limited to) the following steps: substrate surface cleaning, gluing, baking, exposure, development, fixing, etching (dry or wet), degumming and cleaning again. Obviously, the entire photolithography process involves many complicated processes and exposure to various chemical reagents, so problems such as oxidation, pollution, introduction of lattice defects (damage damage) and low processing efficiency and high cost are unavoidable. In addition, it is difficult to do to achieve atomic layer precision etch removal of materials. In addition, there are many application devices that require epitaxial growth of new materials on the prepared micro-nano structure after the material is processed (such as the current use of pattern substrates to grow periodic quantum dots). Obviously, this ex-situ lithography method is due to The many shortcomings mentioned above cannot guarantee the crystal quality of subsequent materials at all. Therefore, it is of great application value to invent a process that can directly realize the structural processing of materials in situ in the molecular beam epitaxy system (in this way, the complete integration of material growth and material processing will be realized).

Contents of the invention

The present invention aims to provide an in-situ laser interference lithography method based on molecular beam epitaxy, which uses traditional laser interference to implement structured photolithography on materials in situ on molecular beam epitaxy systems. The micro-nano processing method of materials has no pollution, no oxidation, low material damage, and the process is extremely simple and efficient; in addition, the etching accuracy of materials in the Z direction can reach the atomic level.

According to the technical solution of the present invention, the in-situ laser interference lithography method based on molecular beam epitaxy includes the following steps,

S1: heating the substrate, the substrate is a Ga-based or Al-based material, and the heating temperature is higher than the thermal desorption temperature of the In-based material corresponding to the substrate material;

S2: Introduce an In atomic flow to act as a surface catalyst, introduce laser interference to expose the substrate, and complete the photolithography process.

The method provided by the present invention is an in-situ In element-assisted laser interference lithography technology, which is based on the molecular beam epitaxy system using laser interference to write III-V compound semiconductor materials in situ. For III-V compound semiconductor materials The thermal stability of In-based materials is usually worse than that of similar Ga-based or Al-based materials (for example, the thermal desorption temperatures of InAs, InSb, and InN are much lower than those of GaAs, GaSb, GaN, AlAs, AlSb, and AlN, respectively. In addition, since In atoms have the largest atomic size, the doping of In atoms in pure Ga/Al-based materials will introduce a large strain and cause Ga/Al-based materials to become unstable.

Further, the material of the substrate is GaAs, GaSb, GaN, AlAs, AlSb or AlN.

Further, in order to suppress the formation of Ga or Al metal particles from the enrichment of group III elements caused by laser processing, it is necessary to suppress and compensate the larger V group beam current. Therefore, in the step S1, the substrate is heated at V Under the atmosphere of family elements.

Further, the beam current of the group V elements is (1.7-3.0)×10 ^-5 torr.

Further, in the step S1, the heating temperature is 10-20° C. higher than the thermal desorption temperature of the In-based material corresponding to the substrate material.

Specifically, when engraving GaAs or AlAs, it is 10-20°C higher than the thermal desorption temperature of InAs; when engraving GaSb or AlSb, it is 10-20°C higher than the thermal desorption temperature of InSb; when engraving GaN or AlN, it is 10°C higher than the InN thermal desorption temperature. -20°C.

Further, in the step S2, the beam current of the In atomic flow is 0.1-0.3 atomic layer/s.

Specifically, in the step S2, since the temperature of the substrate is higher than the combined crystallization temperature of In and V group elements, the In atoms sprayed onto the surface of the substrate will not form epitaxial films from a macroscopic point of view, but from a microscopic point of view, the In atoms In fact, it will go through the dynamic process of surface adsorption to desorption to leave the surface, but considering that there are always newly sprayed In atoms reaching the surface, it can be considered that there is always a certain amount of In atoms "floating" on the surface. It has been verified by experiments that these In atoms will act as catalysts, greatly improving the activity of Ga/Al atoms in the substrate material.

Further, in the step S2, the exposure method is single-pulse exposure.

Further, in the step S2, the wavelength of the laser is 532-193 nm, the pulse width is 10 ns, and the energy is 4-50 mJ.

Further, in the step S2, after the exposure, the operation of staying under the heating temperature condition in the step S1 is also included. During the staying process, the remaining In atoms on the surface are completely desorbed, and then the temperature can be lowered normally to take it out.

Further, the residence time is 2-5min

Compared with the prior art, the technical solution of the present invention has the following advantages: the photolithography method of the present invention directly relies on the ultra-high vacuum molecular beam epitaxy system in situ, and utilizes the easy heat of In atoms in the field of epitaxial growth of III-V compound semiconductor materials desorption, thereby proposing a photolithography technology in which In atoms act as surface catalytic active agents, and verifying through experiments: the introduction of this auxiliary catalytic process of In atoms of the present invention can achieve almost no damage to materials (the structure surface still retains typical Epitaxial-level atomic layer step morphology) etching process, and in practice, the material removal can be achieved by simply changing the exposure laser energy to achieve single-atom level etching precision in the z direction, and if there is no auxiliary catalysis of In atoms, direct photo If it is engraved, it will lead to serious material modification damage and the structuring effect obtained by etching is very poor; in addition, this method has no pollution, no oxidation, and low material damage compared with other existing ex-situ material micro-nano processing methods. , the process is simple and efficient; in addition, it is particularly worth mentioning that the present invention truly integrates material growth and material processing in situ, and will bring more new possibilities in the development of semiconductor micro-nano structures and device growth in the future.

Description of drawings

Figure 1 is a schematic diagram of the method of the present invention.

FIG. 2 is a diagram of AFM test results in Example 1.

Fig. 3 is a diagram of AFM test results in Examples 2-4.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and implement it, but the examples given are not intended to limit the present invention.

Embodiment 1 etching GaAs material substrate

Step 1, as shown in Figure 1a, set the base temperature of the GaAs substrate on which the GaAs buffer layer has been grown to 545°C (about 15°C higher than the thermal desorption of InAs), and then set the As pressure (As ₄ ) to 2.0×10 ^-5 torr;

Step 2, as shown in Figure 1b, set the beam current of the In source to 0.2 atomic layers/s, and then open the In shutter;

Step 3, as shown in Figure 1c, introduce single-pulse double-beam interference in situ to irradiate the GaAs substrate at this time. The laser parameters used are: wavelength 532nm, pulse width 10ns, energy 18mJ, and immediately turn off the In Shutter and stay at this temperature for 3 minutes, then cool down and take it out.

As shown in Figure 2(a) AFM test results, the laser interference successfully processed grooves with a depth of about 20 atomic layers, and the surface of the entire groove structure still retained the typical atomic layer step morphology. However, if there is no surface catalysis of In atoms proposed in this process, and the laser interference is directly used to act on the pure GaAs surface, as shown in Figure 2(b), a large number of metal particles and nanoparticles appear in the groove. Holes, no clear atomic layer step morphology can be observed on the entire surface of the structure.

Embodiment 2 etching GaAs material substrate

Step 1: Set the base temperature of the GaAs substrate on which the GaAs buffer layer has been grown to 545°C (about 15°C higher than the thermal desorption of InAs), and then set the As pressure (As ₄ ) to 2.0×10 ^-5 torr ;

Step 2, set the beam current of the In source to 0.2 atomic layer/s, and then open the In shutter;

Step 3: Introduce single-pulse double-beam interference in situ to irradiate the GaAs substrate at this time. The laser parameters used are: wavelength 532nm, pulse width 10ns, energy 4.5mJ. After staying for 3 minutes, cool down and take it out.

Embodiment 3 etching GaAs material substrate

Step 2, as shown in Figure 1b, set the beam current of the In source to 0.2 atomic layers/s, and then open the In shutter

Step 3, as shown in Figure 1c, introduce single-pulse double-beam interference in situ to irradiate the GaAs substrate at this time. The laser parameters used are: wavelength 532nm, pulse width 10ns, energy 6mJ, and immediately turn off the In Shutter and stay at this temperature for 3 minutes, then cool down and take it out.

Embodiment 4 etching GaAs material substrate

Step 3, as shown in Figure 1b, introduce single-pulse double-beam interference in situ to irradiate the GaAs substrate at this time. The laser parameters used are: wavelength 532nm, pulse width 10ns, energy 8mJ, and immediately turn off the In Shutter and stay at this temperature for 3 minutes, then cool down and take it out.

As shown in Figure 3, the laser energy is 4.5mJ, 6mJ and 8mJ, and the laser interference processed grooves with a depth of about 1, 2 and 3 atomic layers, respectively.

Embodiment 5 etching AlSb material substrate

In the first step, set the base temperature of the AlSb substrate on which the AlSb buffer layer has been grown to about 10°C higher than the thermal desorption of InSb, and then set the Sb pressure to 1.7×10 ^-5 torr;

Step 2, set the beam current of the In source to 0.1 atomic layer/s, and then open the In shutter;

The third step is to introduce single-pulse double-beam interference in situ to irradiate the AlSb substrate at this time. The laser parameters used are: wavelength 355nm, pulse width 10ns, and energy 18mJ. Cool down and take out after staying for 2min.

Embodiment 6 etching GaN material substrate

Step 1: Set the base temperature of the GaN substrate on which the GaN buffer layer has been grown to about 20°C higher than the thermal desorption of InN, and then set the N pressure (N ₂ ) to 3.0×10 ^-5 torr;

Step 2, set the beam current of the In source to 0.3 atomic layer/s, and then open the In shutter;

Step 3: Introduce single-pulse double-beam interference in situ to irradiate the GaN substrate at this time. The laser parameters used are: wavelength 355nm, pulse width 10ns, energy 18mJ. Cool down and take out after staying for 5min.

In summary, using the thermal desorption characteristics of In atoms, an in-situ molecular beam epitaxy system is proposed for different etching substrates by providing a special thermodynamic epitaxial growth environment, that is, in the higher V group elements ( Determined by the composition of group V elements of the processing object) under the protection of the beam atmosphere, the temperature of the substrate is raised above the thermal analysis temperature of the corresponding In atoms, and then a certain beam of In atoms is sprayed onto the surface of the substrate to act as a "catalyst" The role of the method, and then use the mature laser interference method to directly achieve fast and nearly non-destructive lithography on the substrate, and the control accuracy of the etching depth of this solution can reach the atomic layer level in the Z direction.

Apparently, the above-mentioned embodiments are only examples for clear description, and are not intended to limit the implementation. For those of ordinary skill in the art, on the basis of the above description, other changes or changes in various forms can also be made. It is not necessary and impossible to exhaustively list all the implementation manners here. However, the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims

A method for in situ laser interference lithography based on molecular beam epitaxy, characterized in that it comprises the following steps,

S1: heating the substrate, the substrate is a Ga-based or Al-based material, and the heating temperature is higher than the thermal desorption temperature of the In-based material corresponding to the substrate material;

S2: Introduce an In atomic flow to act as a surface catalyst, introduce laser interference to expose the substrate, and complete the photolithography process.
The in-situ laser interference lithography method based on molecular beam epitaxy according to claim 1, wherein the material of the substrate is GaAs, GaSb, GaN, AlAs, AlSb or AlN.
The in-situ laser interference lithography method based on molecular beam epitaxy according to claim 1, characterized in that, in the step S1, heating the substrate is carried out under the atmosphere of group V elements.
The in-situ laser interference lithography method based on molecular beam epitaxy as claimed in claim 3, wherein the beam flow of the group V elements is (1.7-3.0)×10 -5 torr.
The in-situ laser interference lithography method based on molecular beam epitaxy according to claim 1, wherein in the step S1, the heating temperature is 10-20°C higher than the thermal desorption temperature of the In-based material corresponding to the substrate material. ℃.
The in-situ laser interference lithography method based on molecular beam epitaxy according to claim 1, characterized in that, in the step S2, the beam current of the In atom flow is 0.1-0.3 atomic layer/s.
The in-situ laser interference lithography method based on molecular beam epitaxy according to claim 1, wherein in the step S2, the exposure method is single-pulse exposure.
The in-situ laser interference lithography method based on molecular beam epitaxy according to claim 1, wherein in the step S2, the wavelength of the laser is 532-193 nm, the pulse width is 10 ns, and the energy is 4-50 mJ.
The in-situ laser interference lithography method based on molecular beam epitaxy according to claim 1, characterized in that, in the step S2, after the exposure, the operation of staying under the heating temperature condition in the step S1 is also included.
The in-situ laser interference lithography method based on molecular beam epitaxy as claimed in claim 9, wherein the residence time is 2-5min.