Control system and method for diffusing a carrier gas

Abstract

The present application provides a kind of control system of diffusion source gas, comprising: source bottle, gas supply pipe is supplied to the bottom of source bottle with source gas, weighing unit is weighed to source bottle in real time, flow regulating unit is corrected in real time according to the real-time weight obtained by weighing unit to set flow.The present application also provides a kind of control method of diffusion source gas.The present application can monitor and dynamically adjust in real time to diffusion passage source, response is faster, and process stability is good.The present application can improve the stability of diffusion process, can reduce diffusion anomaly, and reduce the rework proportion caused by sheet resistance anomaly.

Description

Technical Field

[0001] This invention relates to a control system and method for a diffusion source gas. Background Technology

[0002] Currently, in the field of solar cell manufacturing, the fabrication of PN junctions is the core process of the cell, and the thermal diffusion process is the most widely used technology for fabricating PN junctions. The diffusion process involves introducing an impurity source into a high-temperature furnace tube, creating a specific process atmosphere, and utilizing the property of matter moving from high concentration to low concentration to incorporate impurity atoms into the semiconductor, thereby forming a PN junction. In the field of solar cells, liquid sources are typically used for diffusion. When process gas is introduced into the impurity source, the gas carries a certain amount of impurity source molecules, which are then carried into the furnace tube to form a diffusion atmosphere. The amount of impurity source carried is related to the flow rate of the carrying gas and the content of the impurity source in the carrying gas. The gas flow rate can generally be precisely controlled using a mass flow meter. The impurity source is usually stored in a constant-temperature chamber, where the temperature is constant and the pressure inside the chamber is close to standard atmospheric pressure. Under these constant temperature and pressure conditions, if the content of the impurity source in the gas reaches its saturated vapor pressure, the amount of impurity source carried into the diffusion furnace by a certain flow rate of gas will be constant. Therefore, the amount of diffusion source can be indirectly controlled by controlling the flow rate of the carrier gas.

[0003] The diffusion effect is generally characterized by sheet resistance, which is related to the surface diffusion concentration and junction depth, and is a key monitoring parameter of the diffusion process. The higher the diffusion concentration and the deeper the junction, the smaller the corresponding sheet resistance. The diffusion process control will limit the sheet resistance to a range, and exceeding the range is considered unacceptable.

[0004] The following problems often occur during diffusion source transmission:

[0005] A) Under constant gas flow rate and diffusion source temperature, as the amount of solution in the source bottle is consumed and the solution height decreases, the sheet resistance will gradually increase. During the service life of the source bottle, the process needs to be adjusted frequently to ensure the stability of the sheet resistance. Frequent adjustments will cause the diffusion sheet resistance to be unstable.

[0006] B) Especially in the initial stage of changing the source bottle and when the solution height in the source bottle is <2cm, the large difference in the corresponding carrier gas flow rate can easily cause abnormal sheet resistance and rework, affecting normal production. Prematurely changing the source bottle would waste the source. The root cause of this problem is that during the process of carrying gas through the liquid source, the gas-liquid contact time is short, the gas-liquid contact area is limited, and the gas cannot form a saturated state for the source, thus failing to provide a constant diffusion source. As the source liquid level decreases, the contact time between the bubbles and the source shortens, and the source content in the gas decreases. If the gas flow rate is not adjusted in time, the diffusion sheet resistance will continuously increase, and in severe cases, rework and other abnormalities may occur.

[0007] Existing patents use photoelectric sensors to monitor the liquid level in the source bottle and add an auxiliary source bottle to replenish the main source bottle to maintain the liquid level. This technology requires a specially designed source bottle and cannot be applied to the conventional source bottles currently in widespread use. Furthermore, the design only works when the liquid level is close to the lower control limit, resulting in low control accuracy, and therefore it is rarely used. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a control system for a diffusion source gas, comprising:

[0009] The source bottle is used to store the liquid diffusion source and has a source gas output terminal on the top.

[0010] The gas supply pipe supplies the source gas to the bottom of the source bottle;

[0011] The weighing unit weighs the source bottle containing the liquid diffusion source in real time and obtains the real-time weight.

[0012] The flow regulation unit receives the set flow rate for flow control of the gas supply pipe, and corrects the set flow rate in real time according to the real-time weight obtained by the weighing unit to obtain the real-time corrected flow rate. The correspondence between the real-time corrected flow rate, the set flow rate, and the real-time weight obtained by the weighing unit conforms to a preset formula, and the gas flow rate in the gas supply pipe is adjusted to the real-time corrected flow rate.

[0013] The present invention also provides a method for controlling a diffusion source gas, which employs the above-described control system, and the control method includes:

[0014] When the power source is turned on and during the power source process, the set flow rate of the gas supply pipe (i.e. the set flow rate of the source gas) is determined according to the process requirements of diffusion power source.

[0015] Furthermore, when the power source is turned on and during the power source process, the weighing unit weighs the source bottle containing the liquid diffusion source in real time and obtains the real-time weight.

[0016] Furthermore, when the power supply is turned on and during the power supply process, the flow regulation unit corrects the set flow rate in real time based on the real-time weight obtained by the weighing unit, so as to obtain the real-time corrected flow rate. This ensures that the correspondence between the real-time corrected flow rate, the set flow rate, and the real-time weight obtained by the weighing unit conforms to the preset formula, and adjusts the gas flow rate in the gas supply pipe to the real-time corrected flow rate.

[0017] For details of the diffusion source gas control system and control method of the present invention, please refer to the embodiments.

[0018] The advantages and beneficial effects of this invention are as follows:

[0019] This invention can correct the flow rate of the source gas in real time based on the weight of the source bottle, thereby achieving dynamic adjustment of the source gas flow rate. It can keep the amount of diffusion source entering the diffusion furnace stable while keeping the set flow rate constant.

[0020] This invention can monitor the remaining amount of liquid diffusion source in the source bottle based on the weighing of the source bottle. When the remaining amount of liquid diffusion source is low to a certain level (the real-time weight obtained by the weighing unit is less than the lower limit weight), an alarm is triggered to remind the user to replace the source bottle or replenish the liquid diffusion source.

[0021] This invention can use an external weighing unit (weighing sensor) to weigh the source bottle in real time without changing the internal structure of the existing source bottle. It is suitable for existing source bottles (source bottles with a straight cylindrical inner cavity), and the installation position of the added related units is relatively flexible (as long as it is outside the source bottle). It can be implemented by modifying old equipment or directly integrated into new equipment, thus having a wider range of applications.

[0022] This invention enables real-time monitoring and dynamic adjustment of diffusion sources, resulting in faster response and better process stability.

[0023] This invention can improve the stability of the diffusion process, reduce diffusion anomalies, and reduce the rework rate caused by sheet resistance anomalies. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the present invention. Detailed Implementation

[0025] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0026] In solar cell fabrication, the diffusion process typically uses a liquid diffusion source. To introduce the liquid diffusion source from the source bottle into the diffusion furnace, a source carrier gas (such as inert gas N2) is introduced into the bottom of the source bottle through a gas supply pipe. The gas enters the liquid diffusion source and generates bubbles. The source carrier gas carrying the liquid diffusion source is output from the top of the source bottle (source carrier gas output end) into the diffusion furnace. The amount of source entering the diffusion furnace can be controlled by controlling the temperature of the liquid diffusion source and the flow rate of the source carrier gas.

[0027] The molar content of the liquid diffusion source carried by the source gas is:

[0028]

[0029] Where M is the molar flow rate (mol / min), P1 is the liquid vapor pressure (mmHg) of the liquid diffusion source at a certain temperature, and P CVc is the pressure of the source gas (mmHg) and Vc is the flow rate of the source gas (sccm).

[0030] In a diffusion system, Pc can be precisely controlled by the pressure reducing valve of the gas source connected to the gas supply pipe. Therefore, to ensure a constant M, it is necessary to ensure a constant P1Vc. The flow rate Vc of the source gas is generally set by a program and controlled by a mass flow controller, and its value fluctuates very little. P1, however, is affected by the temperature of the liquid diffusion source and the residence time of the source gas in the liquid diffusion source. Its value is a function of the saturated vapor pressure Ps of the liquid diffusion source and the residence time t of the source gas in the liquid diffusion source: P1 = f(P S ,t);

[0031] At a certain temperature, the saturated vapor pressure Ps of the liquid diffusion source is constant, while the residence time t of the source gas in the liquid diffusion source is greatly affected by the liquid surface height of the liquid diffusion source. As the liquid surface height of the liquid diffusion source decreases with the consumption of the liquid, the residence time of the source gas in the liquid diffusion source is shortened, which in turn leads to a decrease in the source vapor pressure evaporated into the gas. The amount of source that the same flow rate of gas can carry is reduced, ultimately resulting in an increase in the sheet resistance after diffusion.

[0032] To address the shortcomings of existing technologies, this invention provides a control system for a diffusion source gas, comprising:

[0033] The source bottle is used to store the liquid diffusion source; the inner cavity of the source bottle is a vertical column (the cross-sectional shape and area of ​​the inner cavity at each height position of the source bottle remain unchanged, such as the inner cavity of the source bottle can be cylindrical); the top of the source bottle is provided with a source gas output end; the source gas output end is connected to the diffusion furnace through an output pipe, and a one-way valve is provided on the output pipe.

[0034] The gas supply pipe supplies source gas to the bottom of the source bottle; the gas supply pipe can pass through the top of the source bottle and extend into the bottom of the source bottle, and the bottom end of the gas supply pipe is the output end that outputs source gas into the source bottle.

[0035] A weighing unit that weighs a source bottle containing a liquid diffusion source in real time and obtains the real-time weight; the weighing unit may include a weighing sensor located below the source bottle and supporting the source bottle.

[0036] The flow regulation unit receives a set flow rate for flow control of the gas supply pipe, and corrects the set flow rate in real time according to the real-time weight obtained by the weighing unit to obtain a real-time corrected flow rate. The correspondence between the real-time corrected flow rate, the set flow rate, and the real-time weight obtained by the weighing unit conforms to a preset formula, and the gas flow rate in the gas supply pipe is adjusted to the real-time corrected flow rate. The flow regulation unit may include a mass flow controller installed on the gas supply pipe.

[0037] The alarm unit issues an alarm when the real-time weight obtained from the weighing unit is less than the lower limit weight.

[0038] The present invention also provides a method for controlling the diffusion source gas, which employs the above-described control system, and the control method includes:

[0039] Before activating the source, determine in advance the weight M of the empty source bottle (the source bottle does not contain a liquid diffusion source). 瓶 The original total weight M0 of the source bottle containing the liquid diffusion source (the liquid diffusion source in the source bottle has not yet been used), the height difference H0 between the outlet of the gas supply pipe and the bottom surface inside the source bottle (the outlet of the gas supply pipe is located inside the source bottle and directly above the bottom surface inside the source bottle), the area S of the bottom surface inside the source bottle, and the density ρ of the liquid diffusion source in the source bottle. 源 The minimum height difference H between the liquid surface of the liquid diffusion source and the output end of the gas supply pipe min ;

[0040] When the source is turned on and during the process, the set flow rate of the gas supply pipe (i.e. the set flow rate of the source gas) is determined according to the process requirements of the diffusion source, and the temperature of the liquid diffusion source in the source bottle is kept constant.

[0041] After the power supply is turned on, if the alarm unit does not issue an alarm, the source gas (such as inert gas N2) is introduced into the bottom of the source bottle through the gas supply pipe. The output end of the gas supply pipe is located below the liquid surface of the liquid diffusion source. The gas enters the liquid diffusion source and generates bubbles. The source gas carrying the liquid diffusion source is output from the source gas output end at the top of the source bottle to the diffusion furnace.

[0042] Furthermore, when the power source is turned on and during the power source process, the weighing unit weighs the source bottle containing the liquid diffusion source in real time and obtains the real-time weight.

[0043] Furthermore, when the power supply is turned on and during the power supply process, the flow regulation unit corrects the set flow rate in real time based on the real-time weight obtained by the weighing unit to obtain the real-time corrected flow rate, so that the correspondence between the real-time corrected flow rate and the set flow rate and the real-time weight obtained by the weighing unit conforms to the preset formula, and adjusts the gas flow rate in the gas supply pipe to the real-time corrected flow rate.

[0044] Furthermore, if the real-time weight obtained by the weighing unit is less than the lower limit weight when the power is turned on and during the power-on process, the alarm unit will issue an alarm.

[0045] The control system and control method for the diffusion source gas provided by this invention use the following preset formula and calculation formula for the lower limit weight:

[0046] 1) The preset formula is:

[0047]

[0048] Among them, LX To adjust the flow rate in real time, L1 is the set flow rate, and M... 瓶 M0 is the weight of the empty source bottle (the source bottle does not contain a liquid diffusion source), and M0 is the original total weight of the source bottle containing the liquid diffusion source (the liquid diffusion source in the source bottle has not yet been used). X The real-time weight obtained by the weighing unit is given by h0, which is the height difference between the gas supply pipe output end and the bottom surface of the source bottle (the gas supply pipe output end is located inside the source bottle and directly above the bottom surface of the source bottle), S is the area of ​​the bottom surface of the source bottle, and ρ is the weight of the source bottle. 源 The density of the liquid diffusion source in the source bottle.

[0049] 2) The formula for calculating the lower limit weight is:

[0050] M min =(H min +h0)·S·ρ 源 +M 瓶

[0051] Among them, M min M is the lower limit weight. 瓶 H represents the weight of an empty source bottle (the source bottle does not contain a liquid diffusion source). min The minimum height difference (H) between the liquid surface of the liquid diffusion source and the output end of the gas supply pipe. min H is the default value. min (Generally 10-15mm), h0 is the height difference between the outlet end of the gas supply pipe and the bottom surface of the source bottle, S is the area of ​​the bottom surface of the source bottle, ρ 源 The density of the liquid diffusion source in the source bottle.

[0052] like Figure 1 As shown, the reasoning process for the above-mentioned preset formula and the calculation formula for the lower limit weight is as follows:

[0053] Since the residence time of the source gas in the liquid diffusion source is very short (<1s), for the sake of simplifying the analysis process, it can be approximated that the size and volume of the source gas bubble remain unchanged when it rises in the liquid diffusion source, and the rising speed V is constant.

[0054] Let H0 be the initial height difference between the liquid level in the source diffuser and the output end of the gas supply pipe (before the liquid diffuser in the source bottle is used). If the set flow rate of the source gas is L1, and the rise time of the bubble in the liquid diffuser is t1, then...

[0055] After a certain amount of liquid diffusion source is consumed, the height difference between the liquid level of the liquid diffusion source and the output end of the gas supply pipe becomes H. X And the rise time of the bubble in the liquid diffusion source becomes t x ,but

[0056] If the set flow rate L1 of the source gas remains unchanged, in order to keep the actual source-carrying amount of the source gas constant, the real-time correction flow rate L of the source gas should be adjusted accordingly. X It should satisfy t x ×L x =t1×L1, that is

[0057] Since the inner cavity of a conventional source bottle is cylindrical (the cross-sectional shape and area of ​​the source bottle's inner cavity remain unchanged at each height position, such as when the inner cavity of the source bottle is cylindrical), there is a strict correspondence between the change in the liquid level height of the liquid diffusion source and the change in the weight of the liquid diffusion source.

[0058] The weight of the empty source bottle (the source bottle does not contain a liquid diffusion source) is M. 瓶 If initially (before the liquid diffusion source in the source bottle is used) the original total weight of the source bottle containing the liquid diffusion source is M0; after a certain amount of liquid diffusion source is consumed, the real-time weight obtained by the weighing unit is M. X ;but Where S is the area of ​​the bottom surface inside the source bottle, ρ 源 The density of the liquid diffusion source in the source bottle;

[0059] H X Substituting the calculation formula into the above but

[0060] and Where h0 is the height difference between the gas supply pipe output end and the bottom surface of the source bottle;

[0061] but

[0062] When the height difference between the liquid surface of the liquid diffusion source and the output end of the gas supply pipe changes H X When the flow rate of the source-carrying gas is reduced to a certain level, it is difficult to carry out the amount of source required to meet the diffusion source-through process. Therefore, it is necessary to preset the minimum height difference H between the liquid surface of the liquid diffusion source and the output end of the gas supply pipe. min H min The thickness is generally 10-15mm; and it can be determined by checking whether the real-time weight obtained from the weighing unit is less than the lower limit weight M. min To issue an early warning; M min =(H min +h0)·S·ρ 源 +M 瓶 .

[0063] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A control system for a diffusion source gas, characterized in that, include: The source bottle is used to store the liquid diffusion source and has a source gas output terminal on the top. The gas supply pipe supplies the source gas to the bottom of the source bottle; The weighing unit weighs the source bottle containing the liquid diffusion source in real time and obtains the real-time weight. The flow regulation unit receives the set flow rate for flow control of the gas supply pipe, and corrects the set flow rate in real time according to the real-time weight obtained by the weighing unit to obtain the real-time corrected flow rate. The correspondence between the real-time corrected flow rate, the set flow rate, and the real-time weight obtained by the weighing unit conforms to the preset formula, and the gas flow rate in the gas supply pipe is adjusted to the real-time corrected flow rate. The preset formula is: Among them, L X To adjust the flow rate in real time, L1 is the set flow rate, and M... 瓶 M0 is the weight of the empty source bottle, and M0 is the original total weight of the source bottle containing the liquid diffusion source. X The real-time weight obtained by the weighing unit is given by h0, where h0 is the height difference between the gas supply pipe output end and the bottom surface of the source bottle, S is the area of ​​the bottom surface of the source bottle, and ρ is the weight of the source bottle. 源 The density of the liquid diffusion source in the source bottle.

2. The control system for the diffusion source gas according to claim 1, characterized in that, Also includes: The alarm unit issues an alarm when the real-time weight obtained from the weighing unit is less than the lower limit weight.

3. The control system for the diffusion source gas according to claim 1, characterized in that, The weighing unit includes a weighing sensor located below the source bottle.

4. The control system for the diffusion source gas according to claim 1, characterized in that, The flow regulation unit includes a mass flow controller installed on the gas supply pipe.

5. The control system for the diffusion source gas according to claim 1, characterized in that, The source gas output terminal is connected to the diffusion furnace through an output pipe, and a one-way valve is provided on the output pipe.

6. The control system for the diffusion source gas according to claim 1, characterized in that, The inner cavity of the source bottle is cylindrical.

7. The control system for the diffusion source gas according to claim 2, characterized in that, The formula for calculating the lower limit weight is as follows: M min =(H min +h0)·S·ρ 源 +M 瓶 Among them, M min M is the lower limit weight. 瓶 H is the weight of the empty source bottle. min The minimum height difference between the liquid surface of the liquid diffusion source and the output end of the gas supply pipe, where S is the area of ​​the bottom surface inside the source bottle, and ρ is the minimum height difference between the liquid surface of the liquid diffusion source and the output end of the gas supply pipe. 源 The density of the liquid diffusion source in the source bottle.

8. The control system for the diffusion source gas according to claim 7, characterized in that, The H min It is 10-15mm.

9. A method for controlling the diffusion source gas, characterized in that, It employs the control system described in any one of claims 1 to 8, and the control method includes: When the gas supply is turned on and during the gas supply process, the set flow rate of the gas supply pipe is determined according to the process requirements of diffusion gas supply. Furthermore, when the power supply is turned on and during the power supply process, the weighing unit weighs the source bottle in real time and obtains the real-time weight; Furthermore, when the power supply is turned on and during the power supply process, the flow regulation unit corrects the set flow rate in real time based on the real-time weight obtained by the weighing unit, so as to obtain the real-time corrected flow rate. This ensures that the correspondence between the real-time corrected flow rate, the set flow rate, and the real-time weight obtained by the weighing unit conforms to the preset formula, and adjusts the gas flow rate in the gas supply pipe to the real-time corrected flow rate.

10. The method for controlling the diffusion source gas according to claim 9, characterized in that, If the real-time weight obtained by the weighing unit is less than the lower limit weight when the power is turned on and during the power-on process, the alarm unit will issue an alarm.

11. The method for controlling the diffusion source gas according to claim 9, characterized in that, Before activating the power source, determine in advance: the weight M of the empty power source bottle. 瓶 The original total weight M0 of the source bottle containing the liquid diffusion source, the height difference h0 between the outlet of the gas supply pipe and the bottom surface of the source bottle, the area S of the bottom surface of the source bottle, and the density ρ of the liquid diffusion source in the source bottle. 源 .

12. The method for controlling the diffusion source gas according to claim 10, characterized in that, Before activating the power source, determine in advance the minimum height difference H between the liquid level of the liquid diffusion source and the output end of the gas supply pipe. min .

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