Cold shield structure applied to molecular beam epitaxy equipment

Abstract

The invention belongs to the technical field of semiconductor epitaxy, and particularly relates to a cold shield structure applied to molecular beam epitaxy equipment, a cold shield is provided with a cold shield inner shell and a cold shield outer shell, and liquid nitrogen is filled between the cold shield inner shell and the cold shield outer shell; an opening A communicating with the interior of the cold shield inner shell is formed in the top of the upper end closing-in structure, and an opening B communicating with the interior of the cold shield inner shell is formed in the bottom of the lower end closing-in structure; the size of the middle waisted structure is gradually increased from the middle to the upper end and the lower end, multiple sets of beam passing holes are evenly formed in the positions, above the minimum inner diameter of the middle of the middle waisted structure, in the cold shield and the outer shell in the circumferential direction, each set comprises an inner beam passing hole and an outer beam passing hole, and the beam passing holes are formed in the cold shield and the outer shell respectively. The two beam passing holes in each group are sealed; a beam source furnace is mounted on the cavity on the outer side of the middle waisted structure, and an outlet of the beam source furnace corresponds to any group of beam passing holes. The device has a larger surface area, the condensation and adsorption effects on impurities are stronger, and the vacuum degree of the device is improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor epitaxy technology, specifically a cold screen structure applied to molecular beam epitaxy equipment. Background Technology

[0002] In molecular beam epitaxy (MBE) equipment applications, liquid nitrogen is typically introduced into a cold screen to obtain a low-temperature surface. This serves two purposes: firstly, to condense and adsorb gas molecules to provide the ultimate vacuum of the cavity, and secondly, to adsorb impurities during material growth to optimize film quality.

[0003] The most common cold shield structure at present is the "straight cylinder" type, with cylindrical surfaces both inside and out. This existing "straight cylinder" type cold shield structure has a limited low-temperature surface area for adsorbing gas molecules, which affects the vacuum level of the equipment and causes impurities to fall back into the source furnace due to poor condensation and adsorption of impurities, thus contaminating the source material. Summary of the Invention

[0004] In view of the above-mentioned problems of the existing "straight cylinder" cold screen structure, the purpose of this invention is to provide a cold screen structure applicable to molecular beam epitaxy equipment.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] The cold screen of this invention is installed inside a cavity, with the outside of the cavity being an atmospheric environment and the inside being a vacuum environment. The cold screen has an inner shell and an outer shell, and liquid nitrogen flows through the space between the inner shell and the outer shell. The cold screen is divided into an upper constriction structure, a middle constriction structure, and a lower constriction structure from top to bottom. The top of the upper constriction structure has an opening A that communicates with the inside of the inner shell. A substrate stage installed at the top of the cavity passes through opening A and is inserted into the inside of the inner shell. The bottom of the lower constriction structure has an opening B that communicates with the inside of the inner shell. The dimensions of the central waist-shaped structure gradually increase from the middle to both the upper and lower ends. Multiple sets of beam passage holes are evenly opened along the circumference on the inner and outer shells of the cold screen above the smallest inner diameter point in the central waist-shaped structure. Each set of beam passage holes consists of two holes, one inner and one outer, respectively opened on the inner and outer shells of the cold screen, and the two beam passage holes in each set are sealed together. One or more beam source furnaces are installed on the cavity outside the central waist-shaped structure. The outlet of each beam source furnace is located inside the cavity and corresponds to any set of beam passage holes.

[0007] Among them: each group of beam through holes is provided with a shielding ring above it. The shielding ring is located inside the inner shell of the cold screen and is fixed to the inner surface of the inner shell of the cold screen at the middle waist structure.

[0008] The axial centerline of the shielding ring is collinear with the axial centerline of the cold screen, and the projection of each beam on the inner shell of the cold screen through the hole onto the shielding ring is located between the inner and outer rings of the shielding ring.

[0009] Multiple side support tubes are provided along the circumferential direction between the upper and lower closing structures. The upper end of each side support tube is connected to the space between the inner and outer shells of the cold screen at the upper closing structure, and the lower end of each side support tube is connected to the space between the inner and outer shells of the cold screen at the lower closing structure.

[0010] The side support tube is a hollow tube, and an active furnace partition is fixed between the side support tube and the outer surface of the cold screen shell at the middle waist structure.

[0011] The number of spaces formed between two adjacent source furnace partitions is the same as the number of beam through holes. Each source furnace partition is located between two adjacent sets of beam through holes, and a beam source furnace is installed in the space formed between two adjacent source furnace partitions.

[0012] The outlet of each of the beam source furnaces faces obliquely upwards and is collinear with the axial centerline of the beam through-hole of the corresponding group, and intersects with the axial centerline of the cold screen.

[0013] The cold screen is collinear with the axial centerline of the cavity.

[0014] The advantages and positive effects of this invention are as follows:

[0015] 1. The invention provides a novel cold screen structure for use in molecular beam epitaxy equipment. Compared with the traditional "cylindrical" cold screen structure, the cold screen of the present invention has a larger surface area, stronger condensation and adsorption effect on impurities, and improves the vacuum degree of the equipment.

[0016] 2. The beam source furnaces of the present invention are all located outside the middle waist structure, which effectively prevents impurities from falling directly into the furnace mouth and avoids source material contamination.

[0017] 3. The present invention provides a shielding ring above the beam passage hole to further prevent impurities from falling directly into the furnace mouth of the beam source furnace and contaminating the source material.

[0018] 4. The present invention provides a hollow side support tube between the upper and lower end closing structures, which not only strengthens the strength of the waist-closing structure in the middle of the cold screen, but also increases the surface area of ​​the cold screen. Attached Figure Description

[0019] Figure 1 This is a front view of the structure of the present invention;

[0020] Figure 2 This is a front sectional view of the present invention after it has been installed in the cavity and fitted with the beam source furnace;

[0021] Wherein: 1 is the cavity, 2 is the cold screen, 3 is the beam source furnace, 4 is the substrate stage, 001 is the upper end tapering structure, 002 is the middle waist tapering structure, 003 is the lower end tapering structure, 201 is the shielding ring, 202 is the beam passage hole, 203 is the source furnace partition, 204 is the side support tube, 205 is the inner shell of the cold screen, and 206 is the outer shell of the cold screen. Detailed Implementation

[0022] The invention will now be described in further detail with reference to the accompanying drawings.

[0023] like Figure 1 , Figure 2 As shown, the cold shield 2 of the present invention is installed inside the cavity 1. The top of the cavity 1 is provided with a welding flange, and the cold shield 2 is fixedly connected to the welding flange. This is prior art and will not be described in detail. The axial center line of the cold shield 2 and the cavity 1 are collinear.

[0024] The cold screen 2 of the present invention has an inner shell 205 and an outer shell 206, and liquid nitrogen is supplied through the space between the inner shell 205 and the outer shell 206. The cold screen 2 is divided into an upper constriction structure 001, a middle constriction structure 002 and a lower constriction structure 003 from top to bottom. In this embodiment, both the upper constriction structure 001 and the lower constriction structure 003 are hollow cylinders. The top of the upper constriction structure 001 has an opening A0011 that communicates with the interior of the inner shell 205. A substrate platform 4 is fixed to the welding flange of the cavity 1. The substrate platform 4 passes through the opening A0011 and is inserted into the interior of the inner shell 205. The diameter of the opening A0011 is determined by the diameter of the substrate platform 4 and needs to be larger than the diameter of the substrate platform 4. The aperture of opening A0011 is smaller than the inner diameter of the cold screen inner shell 205. This allows the beam generated by the evaporation in the beam source furnace 3 to act not only on the sample (i.e., the substrate stage 4) but also to be directly adsorbed by the inner surface of the cold screen inner shell 205 at the lower and upper end taper structures 001 of opening A0011, instead of acting directly on the cavity 1. This reduces the difficulty of cleaning and maintenance after the equipment is opened. The bottom of the lower taper structure 003 has an opening B0031 that communicates with the interior of the cold screen inner shell 205. Opening B0031 is reserved for monitoring equipment (such as an infrared thermometer) to detect the real-time status of the sample. The aperture of opening B0031 is not critical and should not affect the normal use of the monitoring equipment. Sometimes, depending on the number and type of monitoring equipment, opening B0031 can be changed to multiple through holes evenly distributed along the circumference.

[0025] In this embodiment, the mid-waist structure 002 is an hourglass shape with a central cylinder and frustums at the top and bottom. That is, the size of the mid-waist structure 002 gradually increases from the middle to the top and bottom. Multiple sets of beam passage holes 202 are evenly opened along the circumference on the inner shell 205 and outer shell 206 of the cold screen above the smallest inner diameter point in the middle of the mid-waist structure 002 (i.e., the frustum at the top). Each set of beam passage holes 202 consists of two holes, one inner and one outer, respectively opened on the inner shell 205 and outer shell 206 of the cold screen. The two beam passage holes 202 in each set are sealed, and liquid nitrogen between the inner shell 205 and outer shell 206 of the cold screen cannot enter the beam passage holes 202. One or more beam source furnaces 3 are installed on the cavity 1 on the outer side of the mid-waist structure 002. The outlet of each beam source furnace 3 is located inside the cavity 1 and corresponds to any set of beam passage holes 202. The waist-slimming angle of the central waist-slimming structure 002 and the diameter of the beam through-hole 202 have been rigorously simulated to ensure that the beam generated by the evaporation of the beam source furnace 3 is not obstructed. In this embodiment, the beam source furnace 3 is located outside the central waist-slimming structure 002, effectively preventing impurities from falling directly into the furnace mouth of the beam source furnace 3 and avoiding source material contamination.

[0026] In this embodiment, a shielding ring 201 is provided above each group of beam passage holes 202. Difficult-to-adsorb impurities falling from the upper constriction structure 001 are blocked by the shielding ring 201, further preventing impurities from directly falling into the furnace opening of the beam source furnace 3. In this embodiment, the shielding ring 201 is located inside the inner shell of the cold screen 205 and welded to the inner surface of the inner shell of the cold screen 205 at the middle waist-constriction structure 002. The axial centerline of the shielding ring 201 is collinear with the axial centerline of the cold screen 2, and the projection of each beam passage hole 202 on the inner shell of the cold screen 205 onto the shielding ring 201 is located between the inner and outer rings of the shielding ring 201.

[0027] In this embodiment, between the upper constriction structure 001 and the lower constriction structure 003, multiple side support tubes 204 are evenly distributed along the circumference according to the position and number of beam passage holes 202. The upper end of each side support tube 204 is welded to the upper constriction structure 001 and communicates with the space between the inner shell 205 and the outer shell 206 of the cold screen at the upper constriction structure 001. The lower end of each side support tube 204 is welded to the lower constriction structure 003 and communicates with the space between the inner shell 205 and the outer shell 206 of the cold screen at the lower constriction structure 003. In this embodiment, the side support tubes 204 are hollow tubes, and their number is the same as the number of sets of beam passage holes 202. The side support tubes 204 not only strengthen the strength of the middle constriction structure 002, but also allow liquid nitrogen to pass through inside, increasing the surface area of ​​the cold screen 2, thereby increasing the ability of the cold screen 2 to adsorb impurities.

[0028] In this embodiment, a source furnace baffle 203 is spot-welded to the outer surface of the cold screen shell 206 at the central waist-recessed structure 002 of each side support tube 204. The number of spaces formed between two adjacent source furnace baffles 203 is the same as the number of groups of beam through holes 202. Each source furnace baffle 203 is located between two adjacent groups of beam through holes 202. In this embodiment, a beam source furnace 3 is installed in the space formed between each pair of adjacent source furnace baffles 203, avoiding mutual interference during the evaporation process of the beam source furnace 3. The outlet of each beam source furnace 3 faces obliquely upward and is collinear with the axial center line of the corresponding group of beam through holes 202, and intersects with the axial center line of the cold screen 2.

[0029] The working principle of this invention is as follows:

[0030] The beam output from the beam source furnace 3 enters the cold screen 2 through the beam through hole 202. Liquid nitrogen is filled between the inner shell 205 and the outer shell 206 of the cold screen, as well as in the support tubes 204 on each side, to obtain a low-temperature surface on the cold screen 2. On the one hand, it condenses and adsorbs gas molecules to provide the ultimate vacuum of the cavity, and on the other hand, it adsorbs impurities to optimize the quality of the thin film.

[0031] The present invention aims to increase the surface area of ​​the cold screen 2, enhance the condensation and adsorption of impurities, improve the vacuum degree of the equipment, prevent impurities from falling directly into the furnace mouth of the beam source furnace, and avoid source material contamination, etc.

[0032] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, extensions, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A cold shield structure for use in molecular beam epitaxy equipment, installed inside a cavity (1), wherein the outside of the cavity (1) is an atmospheric environment and the inside of the cavity (1) is a vacuum environment; characterized in that: The cold screen (2) has a cold screen inner shell (205) and a cold screen outer shell (206), and liquid nitrogen is supplied through the space between the cold screen inner shell (205) and the cold screen outer shell (206); the cold screen (2) is divided into an upper end constriction structure (001), a middle waist constriction structure (002) and a lower end constriction structure (003) from top to bottom. The top of the upper end constriction structure (001) is provided with an opening A (0011) that communicates with the inside of the cold screen inner shell (205). The substrate stage (4) installed on the top of the cavity (1) passes through the opening A (0011) and is inserted into the inside of the cold screen inner shell (205). The bottom of the lower end constriction structure (003) is provided with an opening B (0031) that communicates with the inside of the cold screen inner shell; the middle waist constriction structure (002) is provided with an opening A (0011) that communicates with the inside of the cold screen inner shell; the middle waist constriction structure (002) is provided with an opening A (0011) that communicates with the inside of the cold screen inner shell; the lower end constriction structure (003) is provided with an opening B (0031) that communicates with the inside of the cold screen inner shell; the lower end constriction structure (002) is provided with an opening A (001 ... The dimensions of the structure (002) gradually increase from the middle to the upper and lower ends. Multiple sets of beam passage holes (202) are evenly opened along the circumferential direction on the inner shell (205) and outer shell (206) of the cold screen above the smallest inner diameter in the middle of the waist-reducing structure (002). Each set of beam passage holes (202) consists of two holes, one inner and one outer, which are respectively opened on the inner shell (205) and outer shell (206) of the cold screen. The two beam passage holes (202) in each set are closed. One or more beam source furnaces (3) are installed on the cavity (1) outside the middle waist-reducing structure (002). The outlet of each beam source furnace (3) is located inside the cavity (1) and corresponds to any set of beam passage holes (202).

2. The cold screen structure for molecular beam epitaxy equipment according to claim 1, characterized in that: Each group of beam through holes (202) is provided with a shielding ring (201) above it. The shielding ring (201) is located inside the cold screen inner shell (205) and is fixed to the inner surface of the cold screen inner shell (205) at the middle waist structure (002).

3. The cold screen structure for molecular beam epitaxy equipment according to claim 2, characterized in that: The axial center line of the shielding ring (201) is collinear with the axial center line of the cold screen (2), and the projection of each beam on the inner shell (205) of the cold screen through the hole (202) onto the shielding ring (201) is located between the inner and outer rings of the shielding ring (201).

4. The cold screen structure for use in molecular beam epitaxy equipment according to claim 1, characterized in that: Multiple side support tubes (204) are provided along the circumferential direction between the upper end closing structure (001) and the lower end closing structure (003). The upper end of each side support tube (204) is connected to the space between the inner shell (205) and the outer shell (206) of the cold screen at the upper end closing structure (001), and the lower end of each side support tube (204) is connected to the space between the inner shell (205) and the outer shell (206) of the cold screen at the lower end closing structure (003).

5. The cold screen structure for molecular beam epitaxy equipment according to claim 4, characterized in that: The side support tube (204) is a hollow tube, and an active furnace partition (203) is fixed between the side support tube (204) and the outer surface of the cold screen shell (206) at the middle waist structure (002).

6. The cold screen structure for molecular beam epitaxy equipment according to claim 5, characterized in that: The number of spaces formed between two adjacent source furnace partitions (203) is the same as the number of beam through holes (202). Each source furnace partition (203) is located between two adjacent sets of beam through holes (202). A beam source furnace (3) is installed in the space formed between two adjacent source furnace partitions (203).

7. The cold screen structure for use in molecular beam epitaxy equipment according to claim 1, characterized in that: The outlet of each of the beam source furnaces (3) is obliquely upward and collinear with the axial center line of the beam through hole (202) of the corresponding group, and intersects with the axial center line of the cold screen (2).

8. The cold screen structure for use in molecular beam epitaxy equipment according to claim 1, characterized in that: The cold screen (2) is collinear with the axial centerline of the cavity (1).

Images