Mercury source furnace based on pressure closed-loop control

Abstract

The invention discloses a mercury source furnace based on pressure closed-loop control, the mercury source furnace comprises an evaporation tank, a valve control area and an injection pipe which are communicated in sequence, the injection pipe is installed inside a vacuum chamber, the evaporation tank and the valve control area are located outside the vacuum chamber, the valve control area comprises a throttling component, and the throttling component is connected with the valve control area. And the valve control area adjusts the mercury vapor flow at the downstream of the throttling component by controlling the mercury vapor pressure at the upstream of the throttling component. On the basis of the blocking flow principle, the downstream mercury vapor flow is adjusted by controlling the upstream mercury vapor pressure of the throttling component, the pressure-flow linearity is good, the control precision is high, the response speed is high, meanwhile, the influence of mercury liquid consumption and temperature fluctuation is small, and the beam stability is good.

Description

Technical Field

[0001] The invention relates to the field of semiconductor equipment, and in particular to a mercury source furnace based on pressure closed-loop control. Background Art

[0002] Mercury cadmium telluride infrared detectors have the advantages of fast response speed, high quantum efficiency, and continuously adjustable band gap. They are widely used in high-end application fields such as aerospace, remote monitoring systems, and satellite astronomy. They can cover the entire infrared band from shortwave to very long wave, and detectors in each band have shown excellent performance. Molecular beam epitaxy has the advantages of heteroepitaxial growth, in-situ junction formation, and large-area high flatness, and has become an important method for preparing multi-layer heterojunctions and high-uniformity large-area mercury cadmium telluride materials.

[0003] The design of the mercury source furnace in the molecular beam epitaxy equipment of HgCdTe is extremely critical, which is determined by the particularity of mercury: mercury is liquid at room temperature, the mercury vapor pressure is 2mtorr at room temperature, and the mercury vapor pressure is about 10torr at process temperature. The mercury vapor pressure is extremely sensitive to temperature changes, which is much higher than other solid source materials. For example, at 150℃, the mercury vapor pressure fluctuation should be kept less than ±1%, and the temperature change amplitude should be less than ±0.2℃, which puts a great test on the temperature control accuracy of the mercury source furnace. Another problem caused by the high mercury vapor pressure is the difficulty in accurately controlling the mercury beam. The vacuum of the growth chamber in the non-process state is E-11~E-10torr, and the vacuum in the process state is E-10~E-7torr, of which the mercury beam is E-7~E-4torr. How to quickly turn on the mercury beam without causing overshoot, how to completely shut down the mercury beam without causing retention, how to reduce the impact of mercury liquid consumption and temperature fluctuations, and how to achieve uniform distribution of mercury beam on a large area substrate are all key issues that need to be considered in the design of the mercury source furnace. In addition, the adhesion coefficient of mercury is only one percent to one thousandth of that of tellurium and cadmium. Mercury consumption is the largest during the growth process of mercury cadmium telluride materials, and the loading amount of mercury liquid often restricts the number of sheets of mercury cadmium telluride materials that can be grown continuously.

[0004] There are two common technical routes for existing mercury source furnaces. Technical route one is based on temperature control, which adjusts the mercury beam by controlling the temperature of the mercury liquid in the injection tube. The mercury source furnace based on temperature control has certain limitations. As the mercury liquid is continuously exhausted, the heat capacity of the system gradually decreases, causing the temperature-beam curve to change. Therefore, the mercury source furnace based on temperature control is generally equipped with an online liquid replenishment device to keep the mercury liquid in the injection tube at a certain liquid level range, reducing the change in the system's heat capacity to obtain a stable mercury beam. Technical route two is based on valve control technology. A needle valve driven by a motor is set between the injection tube and the evaporation tank. The mercury beam is adjusted by controlling the opening of the needle valve. The appropriate needle valve opening is selected according to the opening-beam curve calibrated by the pre-process test, but it cannot be detected and adjusted in real time during the process. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a mercury source furnace based on pressure closed-loop control which has high control accuracy, is less affected by mercury liquid consumption and temperature fluctuation, and has good beam stability.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A mercury source furnace based on pressure closed-loop control comprises an evaporation tank, a valve control area and an injection pipe which are connected in sequence, wherein the injection pipe is installed inside a vacuum chamber, the evaporation tank and the valve control area are located outside the vacuum chamber, the valve control area comprises a throttling component, and the valve control area adjusts the mercury vapor flow rate downstream of the throttling component by controlling the mercury vapor pressure upstream of the throttling component.

[0008] As a further improvement of the above technical solution: the valve control area also includes a regulating valve, a pressure gauge, a controller and a regulating drive component for driving the regulating valve to operate, the regulating valve is arranged between the evaporator and the throttling component, the pressure gauge is used to detect the pipeline pressure between the regulating valve and the throttling component, the pressure gauge is connected to the input end signal of the controller, and the regulating drive component is connected to the output end signal of the controller.

[0009] As a further improvement of the above technical solution: an angle valve is provided between the throttling component and the injection pipe.

[0010] As a further improvement of the above technical solution: the regulating valve is a needle valve, and the regulating drive component is a motor.

[0011] As a further improvement of the above technical solution: the pressure gauge is a capacitive pressure gauge, and the controller adopts a PID control method.

[0012] As a further improvement of the above technical solution: the throttling component is a throttling orifice plate, and the diameter of the throttling hole of the throttling orifice plate is 2mm to 8mm.

[0013] As a further improvement of the above technical solution: the evaporator is provided with an evaporator heater, the valve control area is provided with a valve control area heater, and the injection pipe is provided with an injection pipe heater, and the operating temperatures of the evaporator, the valve control area and the injection pipe gradually increase.

[0014] As a further improvement of the above technical solution: the working temperature of the evaporator is 150°C to 200°C, the working temperature of the valve control area is 200°C to 300°C, and the working temperature of the injection pipe is 500°C to 700°C.

[0015] As a further improvement of the above technical solution: the mercury source furnace based on pressure closed-loop control also includes a liquid replenishing device, which includes a liquid replenishing tank, a liquid level gauge for measuring the liquid level of the liquid replenishing tank, and a lifting mechanism for driving the liquid replenishing tank to rise and fall. The bottom of the liquid replenishing tank is connected to the bottom of the evaporation tank through a connecting hose, a liquid replenishing valve is provided on the connecting hose, a drain valve is also provided on the connecting hose, and an air extraction valve is provided on the liquid replenishing tank.

[0016] As a further improvement of the above technical solution: the valve control area, the evaporation tank and the parts of the liquid replenishing device that are in contact with mercury vapor or mercury liquid are made of stainless steel and are connected by welding.

[0017] Compared with the prior art, the advantages of the present invention are as follows: the mercury source furnace based on pressure closed-loop control disclosed in the present invention is based on the blocked flow principle, and regulates the mercury vapor flow rate downstream by controlling the mercury vapor pressure upstream of the throttling component. The pressure-flow linearity is good, and the influence of mercury liquid consumption and temperature fluctuation is small, and the beam stability is good.

[0018] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the mercury source furnace based on pressure closed-loop control of the present invention.

[0020] The reference numerals in the figure indicate: 1. injection pipe; 11. injection pipe heater; 12. mounting flange; 13. injection duct; 2. valve control area; 21. angle valve; 22. throttling component; 23. regulating valve; 24. pressure gauge; 25. controller; 26. regulating drive component; 27. valve control area heater; 3. evaporation tank; 31. evaporation tank heater; 4. liquid replenishing device; 41. liquid replenishing tank; 42. connecting hose; 43. liquid replenishing valve; 44. exhaust valve; 45. drain valve; 46. liquid level gauge; 47. lifting mechanism. DETAILED DESCRIPTION

[0021] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0022] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0023] In the present invention, unless otherwise clearly specified and limited, the terms "assemble", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0024] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] The present invention is based on the principle of choked flow: when the gas flows through a narrow pore, a choked flow phenomenon will be formed when the upstream and downstream pressure difference is large enough. The gas flow rate will mainly depend on the pressure on the upstream high-pressure side, while the pressure on the downstream low-pressure side can be ignored. When the pressure upstream of the throttle hole exceeds the downstream pressure by more than twice (for the mercury source furnace, the pressure of the upstream evaporation tank 3 is in the torr level and the pressure of the downstream vacuum chamber (growth chamber) is at the E-7torr level), the downstream flow rate Q down With upstream pressure P up Linear relationship:

[0026] Q down =C(T,γ,M,r)·P up

[0027] Where C is the conductance at the throttle hole, which is related to the gas temperature T, heat capacity ratio γ, molecular weight M and throttle hole radius r. The conductance C is related to the square root of the temperature Therefore, compared with the mercury source furnace based on temperature control, the mercury source furnace based on pressure control is significantly less affected by mercury liquid consumption and temperature fluctuations, and has good beam stability. On the other hand, under the condition of stable temperature, the mercury vapor flow rate downstream of the throttle hole and the mercury vapor pressure upstream are linearly related. Therefore, the mercury vapor pressure is detected in real time by the pressure gauge 24 and the needle valve opening is adjusted by feedback. The closed-loop control of the upstream mercury vapor pressure can control the downstream mercury vapor flow rate. In summary, compared with temperature control, needle valve control can achieve rapid response; compared with ordinary valve control, pressure feedback can achieve precise control.

[0028] Figure 1An embodiment of the mercury source furnace based on pressure closed-loop control of the present invention is shown, comprising an injection pipe 1 installed inside a vacuum chamber, a valve control area 2, an evaporation tank 3 and a liquid replenishing device 4 located outside the vacuum chamber.

[0029] The injection tube 1 includes a mounting flange 12, an injection conduit 13, an injection tube heater 11 and a temperature measuring thermocouple (not shown in the figure). The mounting flange 12 is used for installation connection with the vacuum chamber. Preferably, the injection conduit 13 is made of PBN material (pyrolytic boron nitride ceramic), and its end nozzle is in a trumpet shape, and the nozzle shape is optimized for beam uniformity on a large area substrate. The injection tube heater 11 adopts a PBN\PG\PBN (pyrolytic boron nitride\pyrolytic graphite\pyrolytic boron nitride) heater, and the temperature measuring thermocouple adopts a K-type thermocouple.

[0030] The pressure closed-loop control is realized by the valve control area 2, which is connected to the injection pipe 1 and the evaporation tank 3 through a pipeline. The valve control area 2 mainly includes an angle valve 21, a throttling component 22 (a throttling orifice plate in this embodiment), a regulating valve 23 (preferably a needle valve, which can achieve fast response), a pressure gauge 24, a controller 25, an adjusting drive component 26 (a motor in this embodiment), a valve control area heater 27 and a temperature measuring thermocouple (not shown in the figure).

[0031] Angle valve 21 is an all-metal angle valve used to isolate the inner and outer parts of the mercury source furnace vacuum chamber. First, the mercury beam can be completely shut off in the non-process state, and the vacuum of the growth chamber will not be affected by the retention of the mercury beam; second, the inside and outside of the mercury source furnace are independent in the maintenance state, and the disassembly and assembly, air extraction and inflation, or liquid replenishment and drainage operations of the outer part of the vacuum chamber will not affect the state of the growth chamber.

[0032] The throttling component 22, the regulating valve 23, the pressure gauge 24, the controller 25, and the regulating drive component 26 constitute a pressure closed-loop control circuit. Along the mercury vapor transmission direction, the throttling component 22 is located at the end of the valve control area 2, and the regulating valve 23 is located at the front end of the valve control area 2. The pressure gauge 24 detects the pipeline pressure between the throttling component 22 and the regulating valve 23. The controller 25 reads the pressure value and controls the regulating drive component 26 to drive the regulating valve 23 to operate, adjust the opening of the regulating valve 23 so that the mercury vapor pressure is maintained at the set value, and adjust the mercury vapor flow rate downstream by controlling the mercury vapor pressure upstream of the throttling component 22.

[0033] Of course, in other embodiments, in addition to the above-mentioned constant pressure control mode, a constant needle valve opening control mode may also be selected.

[0034] Preferably, the diameter of the throttle hole is 2 mm to 8 mm, and the throttle hole plate is made of stainless steel. The throttle holes of different diameters can be switched to achieve different beam adjustment ranges. Preferably, the needle valve adopts a bellows seal and a conical needle tip design. The needle valve is a full stainless steel structure, and the needle rod, valve seat, and bellows are all made of stainless steel. Preferably, the pressure gauge 24 is a capacitive pressure gauge resistant to mercury vapor corrosion at 200°C. Preferably, the controller 25 is a PID controller, and the motor is a servo motor.

[0035] The valve control area heater 27 adopts a resistance heater, and the temperature measuring thermocouple adopts a K-type thermocouple, which mainly heats and controls the temperature of the valves and pipelines in the valve control area 2. However, the electrical end of the pressure gauge 24, the controller 25 and the motor are outside the heating area, and the operating temperature is below 50°C.

[0036] The evaporator 3 is provided with an evaporator heater 31 and a temperature measuring thermocouple (not shown in the figure). Preferably, the evaporator 3 is made of stainless steel. Since the liquid replenishing device 4 is provided, the capacity of the evaporator 3 can be slightly smaller, such as 500cc. The evaporator heater 31 is a resistance heater, and the temperature measuring thermocouple is a K-type thermocouple.

[0037] The refilling device 4 is based on the principle of communicating vessels, and includes a refilling tank 41, a connecting hose 42 (a metal hose in this embodiment), a refilling valve 43, an exhaust valve 44, a drain valve 45, a liquid level meter 46 and a lifting mechanism 47, which can replenish mercury liquid for the evaporation tank 3 without destroying the vacuum environment of the growth chamber. Preferably, the refilling tank 41 is made of stainless steel and has a capacity greater than 1000cc. The metal hose connects the bottom of the evaporation tank 3 and the bottom of the refilling tank 41. Preferably, the metal hose is specifically made of stainless steel. The refilling valve 43 is located in the middle of the metal hose and is used to control the connection or disconnection of the refilling pipeline. The exhaust valve 44 is located at the top of the refilling tank 41, and can be connected to an external vacuum pump group or an air circuit for exhaust or inflation operations, or can be used with a dedicated funnel through the exhaust valve 44 for refilling operations. The drain valve 45 is connected to the metal hose for emptying the liquid tanks on both sides. The liquid level meter 46 can directly reflect the liquid level in the liquid replenishment tank 41 and indirectly reflect the liquid level in the evaporation tank 3 (when the tanks on both sides are in a connected and balanced state). The liquid level meter 46 has multiple monitoring gears, such as exhaustion level, low liquid level, medium liquid level, high liquid level, and full liquid level, and performs software display and early warning. The height of the liquid replenishment tank 41 can be adjusted by the lifting mechanism 47, and the liquid replenishment valve 43 is opened. When the liquid level of the liquid replenishment tank 41 is higher than the liquid level of the evaporation tank 3, mercury liquid is added to the evaporation tank 3. When the liquid level of the liquid replenishment tank 41 is lower than the liquid level of the evaporation tank 3, mercury liquid is withdrawn from the liquid replenishment tank 41. The liquid replenishment tank 41 can also be additionally equipped with a liquid injection port, an observation window, etc.

[0038] The containers, pipelines and components in the valve control area 2, evaporation tank 3 and liquid replenishing device 4 that are in direct contact with mercury vapor or mercury liquid are mainly made of stainless steel, and the connection method is mainly welding rather than flange connection, so as to maximize corrosion resistance and airtightness.

[0039] The working temperature of the evaporator 3 is 150℃~200℃, the working temperature of the valve control area 2 is 200℃~300℃, the working temperature of the injection pipe 1 is 500℃~700℃, and the liquid replenishing device 4 works at room temperature. The evaporator 3, the valve control area 2, and the injection pipe 1 use PID controllers to control the temperature in different zones, so that the temperature gradient gradually increases from bottom to top along the mercury vapor transmission path. Preferably, the valve control area 2 and the evaporator 3 are equipped with a tightly fitting outer insulation cover to prevent the occurrence of local low temperature points on the transmission path, which causes the mercury vapor to condense and reflux in the pipeline or valve.

[0040] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the technical content disclosed above without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should fall within the scope of protection of the technical solution of the present invention.

Claims

1. A mercury source furnace based on pressure closed-loop control, characterized in that: The invention comprises an evaporation tank (3), a valve control area (2) and an injection pipe (1) which are connected in sequence, wherein the injection pipe (1) is installed inside a vacuum chamber, the evaporation tank (3) and the valve control area (2) are located outside the vacuum chamber, the valve control area (2) comprises a throttling component (22), and the valve control area (2) adjusts the mercury vapor flow rate downstream of the throttling component (22) by controlling the mercury vapor pressure upstream of the throttling component (22).

2. The mercury source furnace based on pressure closed-loop control according to claim 1, characterized in that: The valve control area (2) further comprises a regulating valve (23), a pressure gauge (24), a controller (25), and a regulating drive component (26) for driving the regulating valve (23) to operate; the regulating valve (23) is arranged between the evaporation tank (3) and the throttling component (22); the pressure gauge (24) is used to detect the pipeline pressure between the regulating valve (23) and the throttling component (22); the pressure gauge (24) is connected to an input end signal of the controller (25); and the regulating drive component (26) is connected to an output end signal of the controller (25).

3. The mercury source furnace based on pressure closed-loop control according to claim 2, characterized in that: An angle valve (21) is provided between the throttling component (22) and the injection pipe (1).

4. The mercury source furnace based on pressure closed-loop control according to claim 2, characterized in that: The regulating valve (23) is a needle valve, and the regulating drive component (26) is a motor.

5. The mercury source furnace based on pressure closed-loop control according to claim 2, characterized in that: The pressure gauge (24) is a capacitive pressure gauge, and the controller (25) adopts a PID control method.

6. The mercury source furnace based on pressure closed-loop control according to claim 1, characterized in that: The throttling component (22) is a throttling orifice plate, and the diameter of the throttling hole of the throttling orifice plate is 2 mm to 8 mm.

7. The mercury source furnace based on pressure closed-loop control according to any one of claims 1 to 6, characterized in that: The evaporator (3) is provided with an evaporator heater (31), the valve control area (2) is provided with a valve control area heater (27), and the injection pipe (1) is provided with an injection pipe heater (11), and the operating temperatures of the evaporator (3), the valve control area (2) and the injection pipe (1) gradually increase.

8. The mercury source furnace based on pressure closed-loop control according to claim 7, characterized in that: The working temperature of the evaporation tank (3) is between 150°C and 200°C, the working temperature of the valve control area (2) is between 200°C and 300°C, and the working temperature of the injection pipe (1) is between 500°C and 700°C.

9. The mercury source furnace based on pressure closed-loop control according to any one of claims 1 to 6, characterized in that: The invention also comprises a liquid replenishing device (4), the liquid replenishing device (4) comprising a liquid replenishing tank (41), a liquid level meter (46) for measuring the liquid level of the liquid replenishing tank (41), and a lifting mechanism (47) for driving the liquid replenishing tank (41) to rise and fall. The bottom of the liquid replenishing tank (41) is connected to the bottom of the evaporation tank (3) via a connecting hose (42). The connecting hose (42) is provided with a liquid replenishing valve (43). The connecting hose (42) is also provided with a liquid drain valve (45). The liquid replenishing tank (41) is provided with an air extraction valve (44).

10. The mercury source furnace based on pressure closed-loop control according to claim 9, characterized in that: The parts of the valve control area (2), the evaporation tank (3) and the liquid replenishing device (4) that are in contact with the mercury vapor or mercury liquid are made of stainless steel and are connected by welding.

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