CN117702259A - Method for quickly cooling PVT furnace - Google Patents

Abstract

This application discloses a method for rapid cooling of a PVT furnace, which includes the following steps: S1: Stop heating the PVT furnace, fill the PVT furnace with cooling gas, the cooling gas is helium, and control the pressure in the PVT furnace until the temperature of the PVT furnace Not exceeding 50℃; S2: Complete the cooling, fill the PVT furnace with inert gas until the pressure in the PVT furnace reaches atmospheric pressure, and take out the crucible. The rapid cooling method of the PVT furnace in this application can greatly shorten the time for the PVT furnace to cool down to normal temperature, thereby improving production efficiency.

Description

A method for rapid cooling of PVT furnace

Technical field

The present application relates to the field of semiconductor growth technology, and specifically to a method for rapid cooling of a PVT furnace.

Background technique

Silicon carbide (SiC) has become a popular material for third-generation semiconductors due to its wide bandgap, high saturation electron mobility, high breakdown electric field and high thermal conductivity. It is widely used in 5G communications, new energy vehicles and photovoltaics. Inverter and other industries.

The preparation methods of third-generation semiconductor silicon carbide single crystals mainly include physical vapor transport (PVT), top seed solution growth (TSSG) and high-temperature chemical vapor deposition (HT-CVD). The PVT method is currently commercialized. Main technical routes.

The synthesis methods of high-purity silicon carbide powder used in the growth of third-generation semiconductor silicon carbide single crystals include: liquid phase method, solid phase method and gas phase method. Among them, the solid-phase method (improved self-propagation method to synthesize silicon carbide, also known as PVT method) to prepare high-purity silicon carbide has the characteristics of high purity, large output and good particle crystallinity, and has been widely promoted.

At present, the most commonly used preparation methods for third-generation semiconductor silicon carbide single crystals and high-purity powders are through PVT furnaces. The PVT furnace is an equipment that implements the PVT method. It uses induction heating to heat the graphite crucible to 2000~2300°C, and grows high-purity SiC crystals and high-purity SiC powder in a quartz tube/stainless steel cavity using the physical vapor transport method (PVT). PVT furnace has the characteristics of high temperature resistance, fast heating speed and good thermal insulation performance.

Because the PVT furnace has good heat preservation performance, its cooling rate is slow. It only takes 5 to 10 hours to heat up the PVT furnace from room temperature to 2200 ℃, but it takes 30 to 40 hours to cool down the PVT furnace from 2200 ℃ to room temperature. The cooling rate of PVT furnace is slow, which greatly reduces its cycle efficiency and cannot achieve optimal production efficiency. Therefore, it is necessary to develop a cost-effective way to speed up the cooling of PVT furnaces.

Contents of the invention

The purpose of this application is to speed up the cooling rate of the PVT furnace.

In order to achieve the above purpose, the technical solution adopted in this application is: a method for rapid cooling of a PVT furnace, which includes the following steps: S1: Stop heating the PVT furnace, and fill the PVT furnace with cooling gas. The cooling gas is helium. Gas, control the pressure in the PVT furnace until the temperature of the PVT furnace does not exceed 50°C; S2: Complete the cooling, fill the PVT furnace with inert gas until the pressure in the PVT furnace reaches atmospheric pressure, and take out the crucible .

Preferably, the purity of the cooling gas and the inert gas is greater than 99.9999%.

As another preference, in step S1, the pressure of the PVT furnace is controlled to 600~800 mbar.

As another preference, the inert gas is argon.

As another preference, step S1 specifically includes: stopping heating of the PVT furnace, filling the cooling gas into the PVT furnace, where the cooling gas is helium, opening the valve of the forced cooling system, and starting all The fan of the forced cooling system uses a heat exchanger to exchange heat and lower the temperature of the cooling gas until the temperature of the PVT furnace does not exceed 50°C.

A method for rapidly cooling a PVT furnace, including the following steps: A1: Stop heating the PVT furnace, fill the PVT furnace with a first cooling gas, the first cooling gas is argon or helium, control the PVT The pressure in the furnace is until the temperature of the PVT furnace does not exceed 1000°C; A2: Extract the first cooling gas in the PVT furnace and fill it with a second cooling gas, and the second cooling gas is hydrogen, Until the temperature of the PVT furnace does not exceed 50°C; A3: Complete the cooling, fill the PVT furnace with inert gas until the pressure in the PVT furnace reaches atmospheric pressure, and take out the crucible.

As another preference, the purity of the first cooling gas, the second cooling gas and the inert gas is greater than 99.9999%.

As another preference, in step A1, the pressure of the PVT furnace is controlled to 600~800 mbar.

As another preference, the inert gas is argon.

Further preferably, the step A2 specifically includes: extracting the first cooling gas and filling it with the second cooling gas, opening the valve of the forced cooling system, starting the fan of the forced cooling system, and using a heat exchanger to The second cooling gas performs heat exchange and cooling until the temperature of the PVT furnace does not exceed 50°C.

Compared with the existing technology, the beneficial effects of this application are:

(1) The rapid cooling method of the PVT furnace in this application can greatly shorten the time for the PVT furnace to drop to normal temperature, thereby improving production efficiency;

(2) The method of rapid cooling of the PVT furnace in this application avoids the introduction of new impurities into the PVT furnace and at the same time reduces the cost of cooling.

Description of the drawings

Figure 1 is a device for rapid cooling of a PVT furnace according to an embodiment of the present application;

In the picture: 1. Graphite crucible; 2. Thermal field; 3. PVT furnace; 4. Forced cooling system; 41. Fan; 42. Heat exchanger; 43. Valve.

Detailed ways

Below, the present application will be further described with reference to specific implementation modes. It should be noted that, on the premise that there is no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

The terms "comprising" and "having" and any variations thereof in the description and claims of this application are intended to cover a non-exclusive inclusion, for example, a process, method, system, product or product that includes a series of steps or units. Apparatus are not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such processes, methods, products or devices.

This application provides a method for rapid cooling of a PVT furnace, which includes the following steps:

S1: Stop heating the PVT furnace, fill the PVT furnace with cooling gas, the cooling gas is helium, and control the pressure in the PVT furnace until the temperature of the PVT furnace does not exceed 50 ℃;

S2: Fill the PVT furnace with inert gas until the pressure in the PVT furnace reaches atmospheric pressure and complete the cooling.

In some embodiments, the PVT furnace is connected to a forced cooling system, and the forced cooling system is equipped with cooling devices such as heat exchangers or fans to increase the cooling rate of the PVT furnace and save time. Through the setting of the heat exchanger in the forced cooling system, the gas in the PVT furnace flows and fully contacts the heat exchanger, which can quickly take away the temperature in the furnace and further increase the cooling speed.

In some embodiments, step S1 is specifically: stop heating the PVT furnace, fill the PVT furnace with cooling gas, the cooling gas is helium, open the valve of the forced cooling system, start the fan of the forced cooling system, and use the heat exchanger to The cooling gas undergoes heat exchange and cooling until the temperature of the PVT furnace does not exceed 50°C.

In some embodiments, the pressure in the PVT furnace is controlled to be 600~800 mbar in step S1.

In some embodiments, the inert gas is inexpensive argon.

In some embodiments, in order to avoid introducing impurities into the PVT furnace, high-purity gases with a purity greater than 99.9999% are selected as cooling gas and inert gas.

This application also provides a method for rapid cooling of a PVT furnace, which includes the following steps:

A1: Stop heating the PVT furnace, fill the PVT furnace with the first cooling gas, the first cooling gas is argon or helium, and control the pressure in the PVT furnace until the temperature of the PVT furnace does not exceed 1000°C;

A2: Extract the first cooling gas from the PVT furnace and fill it with the second cooling gas. The second cooling gas is hydrogen until the temperature of the PVT furnace does not exceed 50°C;

A3: Fill the PVT furnace with inert gas until the pressure in the PVT furnace reaches atmospheric pressure to complete the cooling.

In some preferred embodiments, the PVT furnace is connected to the forced cooling system, and in step A2, after the PVT furnace is filled with the second cooling gas, the valve of the forced cooling system is opened, the fan of the forced cooling system is started, and the The heat exchanger performs heat exchange until the temperature in the PVT furnace does not exceed 50°C.

In some embodiments, step A1 controls the pressure in the PVT furnace to be 600~800 mbar.

In some embodiments, the inert gas is relatively inexpensive argon.

In some preferred embodiments, the first cooling gas, the second cooling gas and the inert gas are all high-purity gases, with a purity greater than 99.9999%, to ensure that the PVT furnace is not contaminated by impurities and to ensure the safe operation of the cooling system.

The interior of the PVT furnace is a closed environment, and heat conduction mainly depends on gas transmission. The heat conduction speed of cooling gases with different thermal conductivity determines the cooling speed. The thermal conductivity of argon is 0.016 W/(m·K), the thermal conductivity of helium is 0.15 W/(m·K), and the thermal conductivity of hydrogen is 0.1805 W/(m·K). It can be seen that , The thermal conductivity of hydrogen is the highest among the three cooling gases. Using hydrogen when cooling the PVT furnace can speed up the cooling rate.

The cooling of the PVT furnace is divided into two stages, and different cooling gases are filled in the two stages. In the A1 stage, argon gas is filled for cooling. When the PVT furnace cools down to below 1000°C, the argon gas in the PVT furnace is extracted. And filled with hydrogen gas.

Since hydrogen will react with the carbon in the PVT furnace at high temperatures, causing pollution in the furnace, argon gas is used to lower the temperature, and then the gas in the PVT furnace is replaced with hydrogen to shorten the cooling time.

Under standard conditions, the thermal conductivity of argon is 0.016 W/(m·K). Argon has limited capabilities in the heat conduction process, but its cost is low compared to other inert gases. Therefore, after cooling in step A2 Fill the PVT furnace with argon gas to keep the air pressure inside and outside the PVT furnace consistent.

When filling the furnace with cooling gas, first quickly fill the PVT furnace with a large flow rate, and maintain a small flow rate during the cooling process to allow the inert gas to fully conduct heat exchange.

This application also provides a device for rapid cooling of a PVT furnace, as shown in Figure 1, including a graphite crucible 1, a thermal field 2, a PVT furnace 3 and a forced cooling system 4. The thermal field 2 has a built-in graphite crucible 1, and the thermal field 2 is loaded with In the PVT furnace 3, the PVT furnace 3 is connected to the forced cooling system 4.

The forced cooling system 4 includes a fan 41, a heat exchanger 42 and a valve 43. The valve 43 is used to control whether the pipeline of the forced cooling system 4 is connected to the PVT furnace 3.

The heat exchanger 42 is a commonly used existing technology. In the figure, the use of cooling circulating water for heat exchange is used as an example.

The PVT furnace 3 is equipped with an induction heating system and a vacuum pressure system. The induction heating system is composed of an induction power supply and an induction coil. The vacuum pressure system in the PVT furnace 3 is composed of a mechanical pump, a molecular pump, a proportional valve, a flow meter and other components. PVT furnace 3 cavity is composed of quartz tubes, metal flanges and other components.

The inside of the thermal field 2 is a graphite barrel. The outside of the graphite barrel is wrapped with 3 to 5 layers of graphite soft felt. The top of the graphite barrel is covered with multiple layers of graphite soft felt, and the bottom of the graphite barrel is provided with graphite hard felt. Both soft graphite felt and hard graphite felt have a thermal insulation effect, and the hard graphite felt placed at the bottom of the graphite barrel also plays a role in supporting the graphite barrel. The purity of graphite soft felt and hard graphite felt is both greater than 99.998%.

Graphite crucible 1 is suitable for being embedded in the graphite barrel of thermal field 2. Graphite crucible 1 includes a graphite body, a graphite upper cover and a graphite lower cover. The graphite upper cover and graphite lower cover are connected to the graphite body using graphite bolts respectively. The purity of the graphite crucible is greater than 99.9999%.

Example 1

In order to test the method of rapid cooling of the PVT furnace in this application, the cooling device shown in Figure 1 is used to first heat up the PVT furnace and then keep it warm for a period of time. The heating and holding steps simulate actual PVT furnace production scenarios

Heating stage: Place the thermal field 2 containing the graphite crucible 1 into the cavity of the PVT furnace 3, set the pressure in the PVT furnace 3 below 1*10 ^-3 mbar, and heat the PVT furnace 3 to 2200°C.

Insulation stage: When PVT furnace 3 reaches 2200 ℃, fill PVT furnace 3 with argon gas, set the pressure in the furnace to 600±2 mbar, keep the temperature in the furnace at 2200±10 ℃, and keep PVT furnace 3 warm for 10 hours .

Cooling stage: S1: PVT furnace 3 stops heating and starts timing, evacuates the argon gas in the furnace, fills helium into PVT furnace 3, and controls the pressure in the furnace to about 800±2 mbar until the temperature of PVT furnace 3 drops to Below 50 ℃;

S2: Fill PVT furnace 3 with argon gas, and stop timing after the pressure in the furnace reaches atmospheric pressure.

Example 2

The temperature rise stage and heat preservation stage in Example 2 remain the same as in Example 1.

Cooling stage: S10: PVT furnace 3 stops heating and starts timing, and controls the pressure in the furnace at 800±2 mbar until the temperature of PVT furnace 3 is reduced to 1000°C;

S11: Evacuate the argon gas in the PVT furnace 3 and fill it with hydrogen, and control the pressure in the furnace at 800±2 mbar until the temperature of the PVT furnace 3 is reduced to below 50°C;

S2: Evacuate the hydrogen in the PVT furnace 3, fill the furnace with argon until the pressure in the furnace reaches atmospheric pressure, and stop the timing.

Example 3

Heating stage: Place the thermal field 2 equipped with the graphite crucible 1 into the cavity of the PVT furnace 3, open the valve 43 of the forced cooling system 4, set the pressure in the PVT furnace 3 below 1*10-3 mbar, and turn off the air Valve 43, and heat PVT furnace 3 to 2200°C.

Insulation stage: When PVT furnace 3 reaches 2200 ℃, fill PVT furnace 3 with argon gas, set the pressure in the furnace to 600±2 mbar, keep the temperature in the furnace at 2200±10 ℃, and keep PVT furnace 3 warm for 10 hours .

Cooling step: S10: PVT furnace 3 stops heating and starts timing. The argon gas in PVT furnace 3 is evacuated and filled with helium. The pressure in the furnace is controlled at 800±2 mbar until the temperature of PVT furnace 3 is reduced to 1500°C;

S11: Open the valve 43 of the forced cooling system 4, start the fan 41, control the pressure in the furnace at 800±2 mbar, and control the inlet water temperature in the heat exchanger 42 within 28 ℃ until the temperature of the PVT furnace 3 drops to 50 ℃ the following;

S2: Fill the furnace with argon gas until the pressure in the furnace reaches atmospheric pressure, and stop the timing.

Example 4

The operating steps of the heating stage and the cooling stage in Example 4 are consistent with those in Example 3.

Cooling step: S10: PVT furnace 3 stops heating and starts timing, fills PVT furnace 3 with argon gas, and controls the pressure in the furnace at 800±2 mbar until the temperature of PVT furnace 3 is reduced to 1000°C;

S11: Evacuate the argon gas in the PVT furnace 3 and fill it with hydrogen, open the valve 43 of the forced cooling system 4, start the fan 41, control the pressure in the furnace at 800±2 mbar, and control the inlet water temperature in the heat exchanger 42 at 28 ℃, until the temperature of PVT furnace 3 drops below 50 ℃;

S2: Fill the furnace with argon gas until the pressure in the furnace reaches atmospheric pressure, and stop the timing.

Comparative example 1

The temperature rise stage and heat preservation stage of Comparative Example 1 remained the same as in Example 1.

Cooling stage: PVT furnace 3 stops heating and starts timing, the furnace is filled with argon gas, and the pressure in the furnace is controlled at about 800±2mbar until the temperature of PVT furnace 3 drops below 50°C;

S2: Fill PVT furnace 3 with argon gas, and stop timing after the pressure in the furnace reaches atmospheric pressure.

Comparative example 2

The operating steps of the heating stage and the cooling stage in Comparative Example 2 are consistent with those in Example 3.

Cooling stage: S10: PVT furnace 3 stops heating and starts timing, the furnace is filled with argon gas, and the pressure in the furnace is controlled at 800±2 mbar until the temperature of PVT furnace 3 is reduced to 1500°C;

S11: Open the valve 43 of the forced cooling system 4, start the fan 41, control the pressure in the furnace at 800±2 mbar, and control the inlet water temperature in the heat exchanger 42 within 28 ℃ until the temperature of the PVT furnace 3 drops to 50 ℃ the following;

S2: Fill the furnace with argon gas until the pressure in the furnace reaches atmospheric pressure, and stop the timing.

The test times of the above-mentioned Examples 1 to 4 and Comparative Examples 1 to 2 are recorded in Table 1 below.

Table 1 Cooling time used in each example and comparative example

Analysis of the comparative results of Examples 1 to 4 and Comparative Examples 1 to 2 shows that the rapid cooling method of the PVT furnace of the present application can shorten the cooling time of the PVT furnace, thereby improving production efficiency. In the optimal cooling scheme, the cooling time can be shortened by about 60%, which means the cooling rate can be increased by 60% at the fastest.

In addition, this application also takes into account the issue of cooling costs, using heat exchangers and fans to increase the cooling rate without significantly increasing costs, and using relatively cheap argon gas to fill the PVT furnace to bring the pressure to atmospheric pressure.

The PVT furnace cooling method and device of the present application have a good cooling effect, can greatly shorten the cooling process time, and improve production efficiency.

The above describes the basic principles, main features and advantages of the present application. Those skilled in the industry should understand that the present application is not limited by the above-mentioned embodiments. What is described in the above-mentioned embodiments and descriptions is only the principle of the present application. The present application will have various applications without departing from the spirit and scope of the present application. changes and improvements that fall within the scope of the claimed application. The scope of protection claimed in this application is defined by the appended claims and their equivalents.

Claims (10)

1. A method for rapid cooling of a PVT furnace, which is characterized by including the following steps: S1: Stop heating the PVT furnace, fill the PVT furnace with cooling gas, the cooling gas is helium, and control the pressure in the PVT furnace until the temperature of the PVT furnace does not exceed 50°C; S2: Complete the cooling, fill the PVT furnace with inert gas until the pressure in the PVT furnace reaches atmospheric pressure, and take out the crucible. 2. The method for rapid cooling of a PVT furnace according to claim 1, wherein the purity of the cooling gas and the inert gas is greater than 99.9999%. 3. The method for rapid cooling of a PVT furnace as claimed in claim 1, wherein in step S1, the pressure of the PVT furnace is controlled to be 600~800 mbar. 4. The method for rapidly cooling a PVT furnace according to claim 1, wherein the inert gas is argon. 5. The method for rapid cooling of a PVT furnace according to any one of claims 1 to 4, wherein the S1 is specifically: the PVT furnace stops heating, and the cooling gas is filled into the PVT furnace, The cooling gas is helium. Open the valve of the forced cooling system, start the fan of the forced cooling system, and use a heat exchanger to perform heat exchange and cooling of the cooling gas until the temperature of the PVT furnace does not exceed 50°C. 6. A method for rapid cooling of a PVT furnace, which is characterized by including the following steps: A1: Stop heating the PVT furnace, fill the first cooling gas into the PVT furnace, the first cooling gas is argon or helium, and control the pressure in the PVT furnace until the temperature of the PVT furnace does not exceed 1000℃; A2: Extract the first cooling gas from the PVT furnace and fill it with a second cooling gas, where the second cooling gas is hydrogen, until the temperature of the PVT furnace does not exceed 50°C; A3: Complete the cooling, fill the PVT furnace with inert gas until the pressure in the PVT furnace reaches atmospheric pressure, and take out the crucible. 7. The method for rapid cooling of a PVT furnace according to claim 6, wherein the purity of the first cooling gas, the second cooling gas and the inert gas is greater than 99.9999%. 8. The method for rapid cooling of a PVT furnace according to claim 6, wherein in step A1, the pressure of the PVT furnace is controlled to be 600~800 mbar. 9. The method for rapidly cooling a PVT furnace according to claim 6, wherein the inert gas is argon. 10. The method for rapid cooling of a PVT furnace according to any one of claims 6 to 9, characterized in that the step A2 specifically includes: extracting the first cooling gas and filling it with the second cooling gas, opening The valve of the forced cooling system starts the fan of the forced cooling system, and uses a heat exchanger to exchange heat and cool down the second cooling gas until the temperature of the PVT furnace does not exceed 50°C.