Method for fixing GaSb substrate in molecular beam epitaxy system and sample holder

Abstract

The invention aims at the shortcomings of the prior art method for fixing a GaSb substrate, namely, that the substrate is easily softened and the temperature uniformity of the substrate is difficult to ensure. The invention provides a method for installing and fixing a GaSb substrate in a molecular beam epitaxy system and a sample holder used therefor. The sample holder comprises a cylinder, a tantalum sheet and a pressing and fixing device. The cylinder and the pressing and fixing device are both made of materials that are non-volatile and do not release gas under ultra-high vacuum. A supporting structure is arranged on the inner surface of the cylinder. The tantalum sheet is arranged on the supporting structure. The pressing and fixing device is located above the tantalum sheet to fix the tantalum sheet in the cylinder. The GaSb substrate is fixed by the method of the invention. First, Ga liquid is coated on an intermediate material, and then the Ga liquid is uniformly coated on the tantalum sheet through the intermediate material. The problem that the wettability of the Ga liquid is poor and it is difficult to uniformly coat the tantalum sheet and the GaSb substrate is cleverly solved. The GaSb substrate is uniformly and firmly bonded to the tantalum sheet, and the problem of temperature uniformity of the GaSb substrate is finally solved, providing a basis for realizing the growth of high-quality Sb compound materials.

Description

Technical Field

[0001] The invention relates to a method for installing and fixing a GaSb substrate in a molecular beam epitaxy system and a sample rack used therefor. Background Art

[0002] In molecular beam epitaxy equipment, the heating of the substrate is mainly carried out by thermal radiation heating from a heater parallel to the substrate. There is a thermal radiation field gradient between the substrate heater and the substrate, and there is also non-uniformity in the temperature field on the plane of the substrate heater. These factors will lead to non-uniform substrate temperature. During the growth process, the substrate is usually set on a sample holder, which is a tray. By rotating the substrate tray, the substrate tray is heated more evenly, thereby improving the uneven heating temperature of the substrate, but the problem cannot be completely solved. The prior art uses a molybdenum tray as a substrate tray, that is, a sample holder. The molybdenum tray is a cylindrical disk made of Mo metal, generally 2-3mm thick, and has the characteristics of large heat capacity and high temperature stability. Therefore, the industry generally uses low-melting-point Ga or In liquid metal to bond the molybdenum tray to the substrate to fix the GaSb substrate on the molybdenum tray to improve the uniformity of the substrate temperature. The above method of fixing the substrate has the following advantages: under normal pressure, the melting points of Ga and In are 30°C and 156°C, respectively. During the molecular beam epitaxial growth of III-V materials, the substrate temperature is about 400-550°C. Therefore, Ga and In are in liquid state during the molecular beam epitaxy process, which can provide good thermal contact for the substrate. In addition, the non-rigid clamping method of the substrate can effectively reduce the strain introduced and the dislocation generated during the molecular beam epitaxial thin film growth process.

[0003] However, when processing materials of 6.1Å material system such as InAs, GaSb, AlSb, etc., the following problems exist when using the above fixing method and sample holder: For 6.1Å material system such as InAs, GaSb, AlSb, GaSb is a commonly used lattice matching substrate. The use of In glue fixation will cause the substrate to soften, resulting in a curved surface on the substrate surface, affecting the quality of the epitaxial material. Compared with In, Ga has a lower melting point and will not form an alloy with GaSb, which has the advantage of being easy to clean. Although using Ga glue can completely avoid the problem of softening the GaSb substrate, Ga has a high reactivity at high temperatures. Long-term use at 550-600°C will cause the molybdenum tray to be gradually corroded, making the molybdenum tray material brittle and reducing its service life. In addition, Ga has poor wettability, and it is also difficult to evenly apply Ga between the molybdenum tray and the substrate, and the uniformity of the substrate temperature is difficult to ensure. Summary of the invention

[0004] The purpose of the present invention is to provide a method for installing and fixing a GaSb substrate in a molecular beam epitaxy system and a sample holder used therefor, in view of the shortcomings of the prior art method for fixing a GaSb substrate, which easily causes the substrate to soften and the temperature uniformity of the substrate is difficult to ensure.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A sample holder for fixing a GaSb substrate in a molecular beam epitaxy system, comprising a cylinder, a tantalum sheet and a clamping and fixing device, wherein the cylinder and the clamping and fixing device are both made of a material that does not volatilize or release gas under ultra-high vacuum, a supporting structure is arranged on the inner surface of the cylinder, the tantalum sheet is arranged on the supporting structure, and the clamping and fixing device is located above the tantalum sheet to fix the tantalum sheet in the cylinder;

[0007] The supporting structure is an annular flange, and the clamping and fixing device is a clamping spring, which can be clamped and fixed in the cylinder;

[0008] The material of the cylinder is molybdenum, and the material of the clamping and fixing device is tungsten;

[0009] The lower end of the support structure is flush with the bottom of the cylinder;

[0010] The cylinder is a cylinder, the tantalum sheet is a disc, the retaining spring is a circular retaining spring, the outer diameter of the retaining spring in a natural state is larger than the inner diameter of the cylinder, and the outer diameter of the retaining spring when the two ends are close together is smaller than the inner diameter of the cylinder.

[0011] A method for fixing a GaSb substrate in a molecular beam epitaxy system, wherein the GaSb substrate is fixed on a tantalum sheet by: firstly applying Ga liquid on an intermediate material, then bringing the intermediate material and the tantalum sheet into face-to-face contact, so that the two move parallel to each other, so that the Ga liquid is evenly applied on the tantalum sheet, and then the GaSb substrate is pasted on the tantalum sheet, wherein the intermediate material is a stable material that does not generate impurities and volatile gases in a high-temperature ultra-high vacuum environment;

[0012] The intermediate material is silicon wafer or gallium arsenide;

[0013] The GaSb substrate is fixed by a sample holder, and Ga is evenly applied on a silicon wafer whose temperature is higher than the melting point of Ga. Then, a cylinder with a tantalum sheet is placed on the silicon wafer and pushed back and forth until Ga is evenly covered on the tantalum sheet.

[0014] Finally, the GaSb substrate is attached to a tantalum sheet that is evenly covered with Ga and heated to a temperature higher than the melting point of Ga, and the GaSb substrate is pushed back and forth until the bubbles in the interface are completely driven out;

[0015] The GaSb substrate is fixed by using the sample holder;

[0016] The heating temperature of the silicon wafer and the tantalum wafer is 50±5C° respectively.

[0017] The sample holder of the present invention uses a tantalum sheet as an intermediate material to directly contact the GaSb substrate. The tantalum has stable properties and is not easy to react with the GaSb substrate or be corroded by Ga. The tantalum has certain ductility and moderate hardness, so it can avoid reacting with the GaSb substrate or being corroded by Ga at high temperature. It is non-volatile in ultra-high vacuum and will not release gas at high temperature, so it will not bring impurities. The tantalum sheet is located on a support structure set on a molybdenum cylinder. The tantalum sheet is fixed to the support structure by a clamping and fixing device, which can prevent the tantalum sheet from moving during use and ensure heating uniformity. The tantalum sheet has a certain hardness, can well support the substrate, will not deform, and perfectly and cleverly solves the technical problems existing in the molybdenum support sample holder of the prior art.

[0018] In the present invention, the tantalum sheet is fixed by a retaining spring, and the opening size of the retaining spring is adapted to the diameter of the circumferential surface of the cylinder body. When fixing the tantalum sheet, it is only necessary to pull the two ends of the retaining spring together to reduce its radial size. After the retaining spring is placed in the cylinder body, the two ends of the retaining spring open under the action of elastic force and are automatically fixed in the cylinder body by the tensioning force, thereby achieving fixation. Therefore, the fixation of the tantalum sheet is simple and easy to operate.

[0019] The method of the present invention is adopted to fix the GaSb substrate, firstly, the Ga liquid is coated on the intermediate material, and then the Ga liquid is uniformly coated on the tantalum sheet through the intermediate material, which ingeniously solves the problem that the Ga liquid has poor wettability and is not easy to be uniformly coated between the tantalum sheet and the GaSb substrate, and the GaSb substrate is uniformly and firmly adhered to the tantalum sheet, and finally the problem of temperature uniformity of the GaSb substrate is solved, providing a basis for realizing the growth of high-quality Sb compound materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a three-dimensional schematic diagram of the structure of a sample rack embodiment of the present invention.

[0021] Figure 2 It is a schematic diagram of the front view of the sample rack embodiment of the present invention.

[0022] Figure 3 A schematic diagram of a support structure provided on a cylinder in a sample rack of the present invention;

[0023] Figure 4 It is a schematic diagram of another embodiment of a support structure provided on the sample holder cylinder of the present invention.

[0024] Description of Reference Numerals

[0025] 1- cylinder; 2- tantalum sheet; 3- pressing and fixing device;

[0026] 4-substrate; 11-support structure DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with specific embodiments:

[0028] The above technical problems have brought certain difficulties to the field and have become technical difficulties that cannot be overcome in the field. In order to solve the above technical problems, the problem of substrate softening caused by In sticking fixation has been studied in depth. We used the Gen II MBE system and tried to fix the GaSb substrate on the molybdenum tray by In sticking and Ga sticking. Through the 580°C heating experiment, it was verified that the In-sticked GaSb substrate softened and a small curved surface was formed on the front of the substrate. Through EDS testing, it was found that the growth surface of the substrate opposite to the In sticking surface had In elements, indicating that GaSb and In formed an InGaSb alloy. In addition, through XRD testing, it was found that the substrate material was still a single crystal, indicating that the softening of the substrate did not come from the erosion and penetration of In. The melting point of InSb is 527°C, and the melting point of GaSb is 712°C. At a high temperature of 550-600°C, the In metal on the back and GaSb dissolve each other to form an InGaSb alloy, where the higher the In content, the lower the melting point. Therefore, the formation of low-melting-point InGaSb alloy by In-bonded GaSb substrate at high temperature is the main reason for the softening of GaSb substrate.

[0029] Based on the above research findings, the present invention provides a sample holder, including a cylinder 1, a tantalum sheet 2 and a clamping spring as a clamping and fixing device 3. The cylinder is made of molybdenum, and a support structure 11 is arranged on the inner circumferential surface of the cylinder. The tantalum sheet 2 is placed flat on the support structure. The axis of the tantalum sheet and the cylinder are preferably perpendicular. The clamping spring is located above the tantalum sheet and presses on the upper surface of the tantalum sheet. The outer side of the clamping spring is clamped and connected with the inner circumferential surface of the cylinder to fix the tantalum sheet on the support structure. Figure 2 As shown, the support structure can be an annular flange or a Figure 3The multiple flanges shown are intermittently distributed along the circumference of the cylinder, and the connecting line of each flange forms a ring. Preferably, the lower end of the support structure is flush with the bottom of the cylinder. Other elastic elements with annular openings can also be used as the clamping and fixing device of the tantalum sheet, for example, an elastic annular sheet with an opening, as long as the annular sheet is pressed into the cylinder and then changes diameter and shrinks to apply elastic force outward, and the elasticity is used to clamp with the inner surface of the cylinder. In order to prevent impurities, the material of the clamping and fixing device is preferably tungsten or other stable materials that do not produce impurities and volatile gases. Of course, the diameter of the retaining ring should be adapted to the diameter of the inner surface of the cylinder. In its natural state, that is, when the two ends are open, the outer diameter of the retaining ring is larger than the inner diameter of the cylinder, and when the two ends are pulled close, it is smaller than the inner diameter of the cylinder to facilitate the clamping into the cylinder. A pressure ring can also be used, and a marble is arranged on the outer circumference of the pressure ring. The diameter of the pressure ring is smaller than the inner diameter of the cylinder. When the marble protrudes outward, the circumference formed by the top of the marble is larger than the inner diameter of the cylinder, which facilitates the pressure ring to be pressed into the cylinder. The support structure and the cylinder can be arranged in an integrated manner or in a separate manner. Of course, the cross section of the cylinder can also adopt other shapes, such as polygonal, elliptical, etc. Accordingly, the tantalum sheet can also adopt polygonal, elliptical shapes.

[0030] The present invention adopts the following method to fix the GaSb substrate:

[0031] The tantalum sheet is fixed to the support structure by means of the pressing and fixing device 3, so that the tantalum sheet is firmly located in the cylinder.

[0032] Use Si wafer as auxiliary coating device, first evenly coat Ga on the silicon wafer heated to a temperature higher than the melting point of Ga; or on the plane of stable material such as GaAs that does not produce impurities and volatile gases. 50±5C°

[0033] Then, the tantalum wafer is brought into contact with the surface of the silicon wafer, and the tantalum wafer and / or the silicon wafer are pushed back and forth to make the two move relatively parallel until Ga is evenly covered on the tantalum wafer; it is best to preheat the Si wafer to 50±5C°.

[0034] Then, place the GaSb substrate on a tantalum sheet that is evenly covered with Ga and heated to a temperature higher than the melting point of Ga. Push the GaSb substrate and / or tantalum sheet back and forth until the bubbles in the interface between the two are completely driven out. Push the GaSb substrate and / or tantalum sheet slowly and carefully to prevent Ga from reaching the front of the GaSb substrate and affecting the quality of epitaxial growth. It is best to heat the Si sheet to 50±5°C in advance.

[0035] For ease of operation, the GaSb substrate is generally fixed in the following manner: Fix the silicon wafer in advance. First, apply Ga evenly on the silicon wafer heated to 50±5°C;

[0036] Then, place the sample holder with the tantalum sheet on the silicon wafer so that the tantalum sheet and the silicon wafer face each other, and push the sample holder back and forth until Ga evenly covers the tantalum sheet.

[0037] Finally, the GaSb substrate is attached to the tantalum sheet that is evenly covered with Ga and heated to 50±5°C. The GaSb substrate is pushed back and forth until the bubbles in the interface between the two are completely driven out. At this time, the Ga liquid basically covers the tantalum sheet when viewed from the side. The GaSb should be pushed slowly and carefully to prevent Ga from reaching the front of the GaSb substrate and affecting the quality of epitaxial growth.

Claims

1. A method for fixing a GaSb substrate in a molecular beam epitaxy system, characterized in that: The GaSb substrate is fixed on the tantalum sheet by the following method: the tantalum sheet is set on the supporting structure, the Ga liquid is first applied on the intermediate material, and then the intermediate material and the tantalum sheet are brought into face-to-face contact so that the two move parallel to each other, so that the Ga liquid is evenly applied on the tantalum sheet, and then the GaSb substrate is pasted on the tantalum sheet. The intermediate material is a stable material that does not produce impurities and volatile gases in a high-temperature ultra-high vacuum environment.

2. The method for fixing a GaSb substrate in a molecular beam epitaxy system according to claim 1, characterized in that: The intermediate material is a silicon wafer or gallium arsenide.

3. The method for fixing a GaSb substrate in a molecular beam epitaxy system according to claim 1, characterized in that: The GaSb substrate is fixed by a sample holder, and Ga is evenly applied on a silicon wafer whose temperature is higher than the melting point of Ga. Then, a cylinder with a tantalum sheet is placed on the silicon wafer and pushed back and forth until Ga is evenly covered on the tantalum sheet. Finally, the GaSb substrate is attached to a tantalum sheet that is evenly covered with Ga and heated to a temperature higher than the melting point of Ga, and the GaSb substrate is pushed back and forth until the bubbles in the interface are completely driven out.

4. The method for fixing a GaSb substrate in a molecular beam epitaxy system according to claim 3, characterized in that: The sample holder comprises a cylinder (1), the tantalum sheet (2) and a clamping and fixing device (3); the cylinder and the clamping and fixing device are both made of a material that does not volatilize or release gas under ultra-high vacuum; the support structure is arranged on the inner surface of the cylinder; the clamping and fixing device is located above the tantalum sheet to fix the tantalum sheet in the cylinder.

5. The method for fixing a GaSb substrate in a molecular beam epitaxy system according to claim 4, characterized in that: The supporting structure is an annular flange, and the clamping and fixing device is a retaining spring, which can be clamped and fixed in the cylinder.

6. The method for fixing a GaSb substrate in a molecular beam epitaxy system according to claim 4, characterized in that: The material of the cylinder is molybdenum, and the material of the clamping and fixing device is tungsten.

7. The method for fixing a GaSb substrate in a molecular beam epitaxy system according to claim 4, characterized in that: The lower end of the supporting structure is flush with the bottom of the cylinder.

8. The method for fixing a GaSb substrate in a molecular beam epitaxy system according to claim 5, characterized in that: The cylinder is a cylinder, the tantalum sheet is a disc, and the retaining spring is a circular retaining spring. The outer diameter of the retaining spring in a natural state is larger than the inner diameter of the cylinder, and the outer diameter of the retaining spring when the two ends are close together is smaller than the inner diameter of the cylinder.

9. The method for fixing a GaSb substrate in a molecular beam epitaxy system according to claim 3, characterized in that: The heating temperature of the silicon wafer and the tantalum wafer is 50±5C° respectively.

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