A control method for a graphite heater used in a CVD device

Abstract

This application discloses a control method for a graphite heater in a CVD device. The control method includes the following steps: a second operation unit of a PLC control module performs a calculation based on a first limiting parameter received from the first operation unit, combined with a second limiting parameter issued by a host computer and a temperature parameter from a temperature controller, to generate a control signal. The control signal is transmitted to a DC power supply, which then receives the control signal and, in response, outputs a voltage or current matching the control signal to the heater. This method, specifically for heating trays in the reaction chamber of a CVD device, can improve temperature control accuracy, produce a smooth and controllable ramp, enhance temperature uniformity within the wafer, and improve product quality.

Description

Technical Field

[0001] The present application relates to the field of semiconductor equipment, and in particular to a control method for a graphite heater used in a CVD device. Background Art

[0002] Graphite, a material characterized by high temperature resistance, high thermal conductivity, low thermal expansion coefficient, and stable performance, is widely used in industry. One of its primary applications is in high-temperature heaters, which operate at temperatures exceeding 2000°C and can withstand repeated and rapid thermal shock. Graphite is widely used as a heating element in thermal equipment such as sintering furnaces, annealing furnaces, and heat treatment furnaces, as well as in semiconductor process equipment such as high-temperature CVD, silicon carbide substrate furnaces, and silicon carbide epitaxial growth equipment.

[0003] As a universal heating product, there are many heating control methods. In terms of hardware: generally divided into AC heating and DC heating;

[0004] Control methods are categorized as voltage control or current control. 1. For equipment requiring an accuracy greater than ±5°C and without strict requirements for the heating curve, heaters are typically powered by a single-phase or three-phase AC power supply and controlled using methods such as fixed-voltage on / off switches or voltage-stepping. 2. For equipment requiring an accuracy greater than ±2°C, phase-shift triggering or zero-crossing triggering are required. 3. Applications requiring high-precision control (within ±1°C), such as silicon carbide epitaxial equipment, cannot employ these simple control methods. This is because the substrate tray temperature must be controlled with an accuracy of ±1°C and the temperature uniformity within the substrate must be maintained within the substrate. Furthermore, strict requirements for the heating curve are also required, requiring a DC power supply and precise software-assisted control. In silicon carbide epitaxial equipment, heaters are often used in a vacuum, hydrogen, or other reactive gas chamber. Furthermore, the high temperatures inherent in the heaters can lead to slow graphite wear and tear, such as sublimation (or evaporation), chemical reactions that cause the heater to gaseous, and frequent thermal expansion and flaking. This shortens the life of the graphite heater and inevitably necessitates replacement. Due to the difference in resistivity of graphite provided by different suppliers, the range of its resistivity is very wide: 10E -6 Ωm-16E -6 Ωm, so after replacing the graphite heater, the voltage and current will be more or less different, requiring a power supply with a larger current and voltage range, and may also have a certain impact on the heating control accuracy.

[0005] In addition, in addition to the differences in resistivity between different types of graphite, the resistivity of graphite itself also changes at different temperatures, such as Figure 1As shown, during the heating process from room temperature to around 800°C, the resistivity typically drops to around 60-70% of its room temperature value. Then, as the temperature rises, the resistivity begins to increase again, reaching 1.1-1.2 times the room temperature value at 1800°C. The resistivity of graphite supplied by different manufacturers varies slightly. Whether using high-precision or low-precision control of a graphite heater, any change in the graphite's resistance inevitably causes changes in the heater's current and voltage. In particular, AC power supply control with fixed or stepped voltages requires the resistance fluctuation range of the graphite heater to be as small as possible. Therefore, using heaters from different manufacturers carries certain risks: the heating curves may vary and become difficult to control smoothly. Excessive resistance differences can also lead to insufficient heating power or excessive current, causing hardware damage. Control methods such as phase-shift triggering, zero-crossing triggering, or DC power supply often require a wide power supply voltage range to accommodate a wide range of graphite heaters. This results in a high maximum current during heating and an unstable heating curve during the heating process. In addition, since the heater itself will sublimate, react, and peel off during use, its cross-sectional area will continue to decrease, causing the total resistance to continue to increase. When the resistance value rises to a certain level, the heater may not reach the required power or heating curve due to the limitation of the power supply voltage, and must be replaced, which will affect the service life. Summary of the Invention

[0006] To overcome these shortcomings, the present application aims to provide a graphite heater control method. This method, specifically for high-precision tray heating applications, can improve temperature control accuracy, produce a smooth and controllable heating and cooling curve, enhance temperature uniformity within the tray, and improve product quality. Furthermore, this method can accommodate a wide range of resistivity variations.

[0007] In order to achieve the above objectives, this application adopts the following technical solutions:

[0008] A control method for a graphite heater of a CVD device, the control method comprising the following steps:

[0009] The second operation unit of the PLC control module performs operation based on the first limit parameter transmitted by the first operation unit and the second limit parameter issued by the host computer and the temperature parameter of the temperature controller to obtain a control signal, and transmits it to the DC power supply.

[0010] The DC power supply receives and responds to the control signal by outputting a voltage or current matching the control signal to the heater. This method, specifically for tray heating applications, can improve temperature control accuracy, produce a smooth and controllable temperature ramp curve, enhance temperature uniformity within the wafer, and improve product quality.

[0011] In one embodiment, the first operation unit of the PLC control module performs operation based on the input maximum value of the DC power supply control signal, the DC power supply rated voltage value and the resistance value R of the heater to obtain the first limiting parameter, and transmits it to the second operation unit.

[0012] In one embodiment, the first limiting parameter is a limited percentage of voltage or current.

[0013] In one embodiment, in the control method of the graphite heater for CVD equipment, the temperature controllers in different temperature sections provide the limiting coefficients r that match the corresponding heating voltages. ctl , the restriction coefficient value is between 0-100%.

[0014] In one embodiment, the second limiting parameter is a limiting coefficient r of the maximum output voltage. max .

[0015] In one embodiment, the control method for a graphite heater for a CVD device re-enters the resistance value of the heater manually.

[0016] In one embodiment, the second operation unit calculates the first limit parameter, the second limit parameter, and the temperature parameter of the temperature controller based on a multiplication method and outputs a control signal.

[0017] In one embodiment, the control signal is a temperature-raising voltage limit value, which is a digital signal or an analog signal.

[0018] In one embodiment, the control signal is expressed in percentages, ranging from 0 to 100%.

[0019] In one embodiment, the temperature controller controls the output to be a voltage signal.

[0020] Beneficial effects

[0021] Compared with the current CVD equipment, each time the graphite heater is replaced, it is necessary to recalculate carefully and then modify the internal setting parameters of the DC power supply to adjust the maximum output parameters of the DC power supply. The process of adjusting the parameters requires professionals to operate, and the process is very complicated and prone to errors. However, the control method of the graphite heater proposed in this application only requires simple operations to complete the parameter adjustment when replacing the heater. This method easily maintains the consistency of the heating power and the heating curve, provides a strong guarantee for ensuring high-precision temperature control, and can greatly extend the service life of the heater. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings are intended to facilitate understanding of the technical solutions of the present disclosure and constitute a part of the specification. Together with the embodiments of the present disclosure, they are used to explain the technical solutions of the present disclosure and do not constitute a limitation of the technical solutions of the present disclosure. The shapes and sizes of the components in the accompanying drawings do not reflect the actual scale and are intended only to illustrate the contents of this application.

[0023] Figure 1 This is a schematic diagram of the resistivity curve of the graphite heater itself at different temperatures;

[0024] Figure 2 This is a schematic diagram of the functional module connections of a graphite heater for a CVD device according to an embodiment of the present application;

[0025] Figure 3 Schematic diagram of a flow chart of a method for controlling a graphite heater according to an embodiment of the present application. DETAILED DESCRIPTION

[0026] The above scheme is further described below with reference to specific examples. It should be understood that these examples are intended to illustrate the present application and are not intended to limit the scope of the present application. The implementation conditions used in the examples can be further adjusted according to the conditions of the specific manufacturer. The implementation conditions not specified are generally those used in routine experiments.

[0027] This application discloses a control method for a graphite heater used in CVD equipment. This control method is designed for high-precision tray temperature control in CVD equipment. This method can improve the temperature control accuracy of high-precision tray heaters, resulting in a smooth and controllable temperature ramp curve, enhancing temperature uniformity within the wafer, and improving product quality, laying a solid foundation for further process advancements. This method can adapt to changes in the heater's resistance, increasing the usable life of the same heater and significantly extending its service life. This method uses a DC power supply capable of receiving an external control signal to control the graphite heater. Both voltage and current control methods can be used.

[0028] The control method for a graphite heater of a CVD device comprises the following steps:

[0029] The second operation unit of the PLC control module performs operation based on the first limit parameter transmitted by the first operation unit and the second limit parameter issued by the host computer and the temperature parameter of the temperature controller to obtain a control signal, and transmits it to the DC power supply.

[0030] The DC power supply receives and responds to the control signal by outputting a voltage or current matching the control signal to the heater (controlling heating of the heater). The CVD apparatus in this method comprises a reaction chamber, a tray disposed at the bottom of the reaction chamber, and a graphite heater disposed below the tray. The graphite heater is connected to an external DC power supply.

[0031] The CVD equipment is equipped with a temperature controller, a PLC control module and a host computer (industrial computer). The functional topology is shown as follows: Figure 2 shown.

[0032] The temperature controller is electrically connected to a thermocouple disposed on the side of a heater (such as a graphite heater) to detect the temperature of the heater. The temperature controller is electrically connected to a host computer to feed back the detected temperature information of the heater.

[0033] The host computer is electrically connected to the PLC control module to exchange information, such as setting a percentage to adjust the temperature control output signal. The PLC control module is electrically connected to a DC power supply to input a control signal (e.g., a voltage signal or a current signal). The DC power supply receives and responds to the control signal by outputting a voltage or current value corresponding to the control signal to heat the heater.

[0034] The PLC control module has a first operation unit and a second operation unit;

[0035] The first operation unit performs operation based on the input DC power supply control signal maximum value (Urang), the DC power supply rated voltage value (Umax) and the heater resistance value R to obtain a first limiting parameter, which is a limited percentage of voltage or current, and transmits it to the second operation unit.

[0036] The second operation unit performs operation based on the received first limit parameter in combination with the second limit parameter issued by the host computer and the temperature parameter of the temperature controller to obtain a control signal, and transmits the control signal to the DC power supply.

[0037] Next, the control method of the graphite heater (hereinafter referred to as the heater) proposed in this application is described using the voltage control method as an example. In this embodiment, all operations are performed by the PLC control module. The control method includes the following steps:

[0038] S1, calculate the maximum voltage U0 of the power supply required by the heater.

[0039] In this step, based on Ohm's law, the electric power of the heater is: P0 = U0 2 / R, get the maximum output voltage required by the heater: U0=(P0·R) 1 / 2 ,

[0040] Where: P0 is the maximum power required by the heater, R is the heater resistance value, and U0 is the maximum voltage of the heater power supply (also called the maximum output voltage).

[0041] S2, calculate the limiting coefficient r of the maximum output voltage of the DC power supply max , the value range is: 0-100%.

[0042] In this step, based on the calculation formula:

[0043] r max =U0 / U max， To obtain the maximum output voltage limit coefficient r of the DC power supply max ,

[0044] Where: r max The limiting factor for the maximum output voltage of the DC power supply

[0045] U max It is the rated output voltage of the DC power supply, and can also be regarded as the maximum output voltage of the DC power supply.

[0046] S3, based on the industrial computer in different temperature ranges, gives the corresponding temperature rise voltage limit coefficient r ctl , the value range is: 0-100%.

[0047] The limiting coefficient r of the heating voltage in this step ctl The limiting factor r of the maximum output voltage of the DC power supply max Multiply them together to get a total output limit coefficient of 0-100%, which is proportional to the control voltage (or current) U output by the temperature controller. temp Multiplying them together gives the input control signal for the heater DC power supply:

[0048] U ctl =r max ··r ctl ·U temp =(P·R) 1 / 2 / U max ·r ctl ·U temp

[0049] Where: r tcl is the limiting coefficient of the temperature rise voltage given by the host computer,

[0050] U temp The analog signal output by the temperature controller is 0-5V, 0-10V or other voltage ranges.

[0051] S4, based on the voltage signal in S3, inputs it to the DC power supply, which receives and responds to the voltage signal and outputs a matching voltage U out To control the heater heating.

[0052] In this step, the voltage U out Based on the calculation formula:

[0053] U out =U ctl / U rang ·U max=(P0·R) 1 / 2 ·r ctl ·U temp / U rang Come get.

[0054] Where: U out U is the voltage of the final DC power supply output to the heater. rang The maximum value of the DC power supply control signal. In this control method, the resistance value R of the graphite heater and the rated output voltage U of the DC power supply should be set in advance during actual operation. max , maximum value of control signal U rang , the maximum heating power P0 of the heater and other information are input to the PLC control module. If the DC power supply is switched later, it is necessary to know U max and U rang The PLC control module can calculate the input signal voltage of the DC power supply according to the above method to control the DC power supply. The DC power supply receives and responds to the voltage information to output a matching voltage U out When the DC power supply is fixed, the heater resistance R and the required maximum power P0 remain unchanged, the output voltage only changes with the output signal U of the temperature controller. temp And the temperature rise voltage limit coefficient r given by the host computer ctl In this control method, the temperature controller's output can only be a voltage signal. If it is a current output, it must be converted to a voltage signal. The temperature controller's input can be a thermocouple or other signal.

[0055] The relevant parameters need to be input into the PLC control module in the early stage of equipment operation. For the same DC power supply, it is only necessary to input the relevant parameters into the PLC control module during equipment installation and commissioning (the first time the U max and U rang Enter the value of U max and U rang , there is no need to re-enter the data later, simplifying the operation process.

[0056] For the input of heater resistance value, manual input mode can be used, such as Figure 2 As shown, each time the resistance value needs to be manually written into the PLC through the host computer or PLC keyboard and stored.

[0057] It can also be in automatic input mode, such as Figure 3As shown, at room temperature, the PLC control module initially outputs a small control voltage to the DC power supply. At this point, it automatically reads the voltage and current across the output heater. Based on this, the PLC control module directly calculates the heater's resistance: R = U / I, and stores it. For example, for a heater with a cold resistance of 0.1Ω, at room temperature, the PLC control module sends a small control voltage to the DC power supply, resulting in an output voltage of approximately 5V. Simultaneously, it automatically reads an output current of approximately 50A, and based on this, calculates a resistance value of 0.1Ω. This allows the automatic heater resistance recording program to be automatically executed each time a new heater is replaced. This method can also be set to run periodically to correct for changes in heater resistance.

[0058] The above embodiments are intended only to illustrate the technical concepts and features of this application. Their purpose is to enable those familiar with the art to understand the content of this application and implement it accordingly. They are not intended to limit the scope of protection of this application. Any equivalent changes or modifications made in accordance with the spirit of this application shall be included in the scope of protection of this application.

Claims

1. A control method for a graphite heater of a CVD device, characterized in that: The control method comprises the following steps: The second operation unit of the PLC control module receives the first limit parameter r transmitted by the first operation unit max Combined with the second limit parameter r issued by the host computer ctl and the temperature parameters of the temperature controller to obtain a control signal, and transmit it to the DC power supply, wherein the first limiting parameter r max The limit percentage of voltage or current is obtained by the first calculation unit of the PLC control module based on the maximum value of the control signal Urang of the input DC power supply, the rated voltage value Umax of the DC power supply and the resistance value R of the heater. The second limit parameter is the limit coefficient r of the corresponding heating voltage given by the temperature controller based on the feedback temperature segment. ctl The limit coefficient value is between 0-100%. The temperature parameter of the temperature controller is the temperature controller output voltage signal U based on the feedback temperature information and the preset model. temp The second operation unit sets the first limit parameter r max , the second limiting parameter r ctl And the temperature parameter U of the temperature controller temp Based on the continuous multiplication method, the control signal is calculated and output. The DC power supply receives the control signal and outputs a voltage or current matching the control signal to the heater in response to the control signal.

2. The control method for a graphite heater of a CVD device according to claim 1, wherein: Enter the heater resistance value manually.

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