Silicon Carbide Crystal Growth Device and Quality Control Method

Provided are a silicon carbide crystal growth device and a quality control method. The device includes: an annealing unit, a crystal growth unit, an atmosphere control unit, and a transport system; the atmosphere control unit provides a gas environment with low water, oxygen and nitrogen; the transport system transports a plurality of target objects after high-temperature purification by the annealing unit to the atmosphere control unit; after assembling silicon carbide seed crystal and silicon carbide powder in a graphite crucible and covering with thermal insulation material to form a container inside the atmosphere control unit, the transport system transports the container to the crystal growth unit. The method uses a weighing system in a chamber of the crystal growth unit to detect a weight change of silicon carbide seed crystal and silicon carbide powder during a crystal growth process through a plurality of weight sensors of the weighing system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a crystal growth device and a quality control method for silicon carbide crystals, which integrates an annealing unit and a crystal growth unit to improve the efficiency of a crystal growth process, and can judge abnormal situations in advance in the crystal growth process by detecting a weight change of a container.

2. The Prior Arts

Silicon carbide (SiC) single crystal (or monocrystal) substrates are categorized as the third generation semiconductors. With the characteristics of high voltage resistance and high frequency, silicon carbide single crystal substrates can be used in power semiconductors in the fields of national defense, aerospace, industry, automobiles and consumer electronics industries.

To produce silicon carbide single crystal substrates, it is necessary to start from growing silicon carbide single crystals. The process is to pour the silicon carbide powder into the graphite crucible disposed inside the thermal insulation material of the container, then put the container into the crystal growth furnace. The silicon carbide powder is sublimated in a high-temperature and closed space, so that the steam of the crystal source powder is condensed and attached to the silicon carbide crystal seed.

The growth of silicon carbide can be said to be a “black box operation”, because it needs to be maintained in a high temperature (greater than 2100° C.) environment during the manufacturing process, and must maintain a low pressure and a long-term stable state. During the process, it is completely impossible to observe the changes in the crystal growth from the outside, which also means that the quality and results of the production can only be revealed at the last moment.

Because the crystallization of silicon carbide in the graphite crucible cannot be observed, to be well controlled so that the atoms of silicon carbide can be properly arranged and attached to the initial silicon carbide seed crystal, in addition to the quality of the silicon carbide seed crystal, other factors such as thermal field design and graphite crucible material affecting the quality of the substrate are also very important.

For the part that the graphite crucible material affects the quality of the substrate, it is known that before silicon carbide growth, it is necessary to use high temperature to anneal the graphite crucible in the container and related components, materials and other targets to purify, so as to prevent the silicon carbide powder loaded into the graphite crucible from being affected by impurities on the graphite crucible.

Traditionally, silicon carbide wafer manufacturers need to send the container containing the graphite crucible and related components to a professional heat treatment company for annealing, or build their own annealing factory before growing the crystal. However, regardless of whether it is an external or a self-built annealing treatment plant, graphite crucibles and related components must return from the annealing treatment place after high-temperature purification treatment, so that they are easily polluted by the external environment during the returning process. If the probability of contamination is to be reduced to a minimum, a clean delivery process must be set up, which is potentially costly. In addition, the transportation of objects such as cavities back and forth between the crystal growth factory and the annealing treatment factory also increases a lot of costs and risks.

SUMMARY OF THE INVENTION

A primary objective of the present invention is to provide a silicon carbide crystal growth device that integrates the annealing unit and the crystal growth unit, and can detect the weight change of the container during the crystal growth process to judge the process abnormality in advance. With the crystal growth device of the present invention, objects such as the container with graphite crucible inside and other components can be annealed and purified without leaving a clean environment, and can be directly transported to the working platform to be filled with silicon carbide powder and other components before transporting to the crystal growth unit to carry out the crystal growth process, and detect the weight change of the container during the crystal growth process to judge the process abnormality in advance; thereby, the engineers can adjust or correct the process in real time according to the situation, and will waste process time because the crystal growth process is completely impossible to observe from the outside, thereby improving the quality and production efficiency of crystal growth, and reducing manufacturing costs.

To achieve the foregoing objective, the present invention provides a silicon carbide crystal growth device, comprising: an annealing unit for performing a high-temperature purification process on a plurality of target objects; a crystal growth unit, used to carry out a crystal growth process on a container contained in the target objects, a silicon carbide seed crystal and a silicon carbide powder placed in a graphite crucible inside of the container; an atmosphere control unit, connected to the annealing unit and the crystal growth unit, and providing a gas environment with low water, oxygen, and nitrogen; wherein the target objects after the high-temperature purification process through the annealing unit being transported to the atmosphere control unit, and after assembling the target objects in the atmosphere control unit, the target objects being transported to the crystal growth unit to carry out the crystal growth process; and a first weighing system, disposed on a first plate of the crystal growth unit for supporting the container, to detect a weight change of the container during the growth process of the silicon carbide crystal, wherein the first weighing system comprises at least two first weight sensors distributed along a periphery of the first plate, and the first weight sensors being electrically connected to a processing unit. As such, the target objects do not need to leave the clean environment after annealing and purification treatment, and can be directly assembled in the clean environment, and then transported to the crystal growth unit for the crystal growth process; and, when the weight sensors located at different positions sense different weight changes, the detected weight can be converted into digital data, sent to the processing unit for analysis and processing, and recorded by a storage unit. By recording the weight change of the container along the crystal growth time axis for early judgment of the quality of crystal growth, engineers can immediately adjust or correct the process in response to the situation when an abnormal situation is found, thereby improving the quality and production efficiency of crystal growth products, and reducing manufacturing costs.

Another embodiment of the present invention may also include: an annealing unit, for performing a high-temperature purification process to the target objects; and an atmosphere control unit, connected to the annealing unit and the crystal growth unit, and providing a gas environment with low water, oxygen, and nitrogen, wherein the target objects after the high-temperature purification process through the annealing unit to be transported to the atmosphere control unit, and after the target objects being assembled in the atmosphere control unit, the target objects then transported to the crystal growth unit for the crystal growth process.

Preferably, the present invention may also include: a transport system, connected to the annealing unit, the atmosphere control unit, and the crystal growth unit, for transporting the target objects after the high-temperature purification process to the atmosphere control unit, and delivering the target objects assembled in the atmosphere control unit to the crystal growth unit.

Preferably, the present invention may also include: a working platform connected to the atmosphere control unit for assembling the target objects.

In an embodiment of the present invention, the transport system may include: a first track, disposed in the atmosphere control unit; a second track, disposed in the annealing unit; a third track, disposed in the crystal growth unit; and a trolley, having a plurality of first wheels to match the first track, and a plurality of second wheels to match the second track and the third track, respectively. Through the transport system, the trolley carries the target objects including the graphite crucible container to move between the closed annealing unit, the atmosphere control unit, and the crystal growth unit, so as to prevent the target objects after annealing and purification from leaving the purification environment, and is less polluted and can be assembled more quickly to improve work efficiency.

Preferably, the first track has a different track gauge from the second track and the third track, the second track has a same track gauge as the third track, and the plurality of first wheels and the plurality of the second wheels have a different wheel distance. With the “broken track” design of different track gauges, the annealing unit, atmosphere control unit, and crystal growth unit can be arranged in environments with height differences or different terrains, so that the transportation of trolleys can be maintained smoothly.

In an embodiment of the present invention, the atmosphere control unit has a gas control system for controlling the contents of water, oxygen, and nitrogen in the atmosphere control unit to be lower than 100 ppm. Thereby, adverse effects of water, oxygen, and nitrogen on the annealed and purified graphite crucible are controlled.

Preferably, the content of water, oxygen, and nitrogen in the atmosphere control unit is controlled in the range of 10 ppm-1 ppb.

Preferably, the gas control system may also include an inert gas supply part and a pressure valve for supplying inert gas into the atmosphere control unit and maintaining a positive pressure above an atmospheric pressure at 760 torr to 770 torr. With the positive pressure maintained in the atmosphere control unit, impurities in the external air can be prevented from entering the atmosphere control unit to cause pollution and affect the quality of the annealed and purified target objects including graphite crucibles.

Preferably, the annealing unit may have an inlet for inserting the target objects that have not been subjected to the high-temperature purification process; the crystal growth unit has an outlet for taking out the target objects that have completed the crystal growth process and crystals; and, the working platform has an inlet and outlet connected to the atmosphere control unit for operating and assembling the target objects.

Preferably, the atmosphere control unit has a thermal exchange system for heat exchange between the inside and outside of the atmosphere control unit.

An embodiment of the present invention may also include: a second weighing system, arranged under a second plate of the annealing unit, to detect the weight change of the container during the high-temperature purification process, the second weighing system comprises at least two second weight sensors distributed along the periphery of the second plate, and the second weight sensors are electrically connected to the processing unit, wherein the first plate and the second plate are discs, and the first weight sensors and the second weight sensors are equiangularly distributed along the circumference of the first plate and the second plate, respectively.

In another embodiment of the present invention, the first plate and the second plate are discs, and the first weight sensors and the second weight sensors are respectively positioned along a circumference of the first plate and the second plate, and are equiangularly and radially distributed.

In an embodiment of the present invention, the first weighing system is used to sense the weight change when the silicon carbide seed crystal is dropped into the graphite crucible of the container, or the weight change caused by skewing and imbalance during the crystal growth process; the second weighing system is used to sense the weight change of the container after impurities are removed during an annealing process.

The present invention also provides a method for controlling the quality of silicon carbide crystal growth, comprising: disposing a first weighing system on a first plate of a crystal growth unit to detect the weight change of a silicon carbide seed crystal and a silicon carbide powder in the graphite crucible of a container during a crystal growth process, wherein the first weighing system has at least two first weight sensors distributed along a periphery of the first plate, the first weight sensors are electrically connected to a processing unit, and each of the first weight sensors send a digital data to the processing unit after independently sensing the weight change of the corresponding position of the container. As such, when the weight sensors at different positions sense different weight changes, it is possible for engineers to adjust or correct the process in real time.

Another embodiment of the quality control method of the present invention may further comprise: connecting an atmosphere control unit between the crystal growth unit and the annealing unit for providing a gas environment with low water, oxygen, and nitrogen, wherein the annealing unit is provided with a second weighing system to detect a weight change of the container placed on the second plate during the high-temperature purification process, wherein the second weighing system has at least two second weight sensors distributed along a periphery of the second plate, the second weight sensors are electrically connected to the processing unit, and each of the second weight sensors send a digital data to the processing unit after independently sensing the weight change of the corresponding position of the container.

According to the quality control method of silicon carbide crystal growth provided by the present invention, the first plate and the second plate are discs, and the first weight sensors and the second weight sensors are respectively positioned along a circumference of the first plate and the second plate, and are equiangularly distributed.

According to the quality control method of silicon carbide crystal growth provided by the present invention, the first plate and the second plate are discs, and the first weight sensors and the second weight sensors are respectively positioned along a circumference of the first plate and the second plate, and are equiangularly and radially distributed.

According to the quality control method of silicon carbide crystal growth provided by the present invention, the first weighing system is used to sense the weight change when the silicon carbide seed crystal is dropped into the graphite crucible of the container, or the weight change caused by skewing and imbalance during the crystal growth process; the second weighing system is used to sense the weight change of the container after impurities are removed during the annealing process.

The present invention detects the weight changes at different positions of the container at any time during the silicon carbide crystal growth process, which helps engineers to instantly understand whether the crystals in production are flawed so as to adjust or correct the process flexibly, without waiting until the long process is completed and the defect is discovered at the end of the crystal, resulting in a waste of process time, thereby improving production efficiency and reducing manufacturing costs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The terminology used herein is used to describe particular embodiments only, and is not intended to limit the present invention. As used herein, the singular terms “a” and “the” are intended to include the plural forms as well, unless the context clearly dictates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present.

As shown inFIG.1andFIG.2, the silicon carbide crystal growth device provided by the present invention integrates an annealing unit1, an atmosphere control unit2, a crystal growth unit3, and a working platform4, so that the graphite crucible7to be loaded with silicon carbide seed crystal and silicon carbide powder does not need to leave a clean working environment from entering the annealing unit1, assembling the silicon carbide seed crystal and silicon carbide powder, covering a thermal insulation material34until completing the crystal growth process and taking out the crystal growth unit. The entire process is completed in one go. As shown inFIG.7, the graphite crucible7is covered with the thermal insulation material34to form a container33after filling silicon carbide seed crystal and silicon carbide powder.

The annealing unit1is the equipment used to carry out high-temperature purification processes for target objects, such as graphite crucible7, silicon carbide seed crystal and silicon carbide powder, before carrying out the crystal growth process. The annealing unit1is provided with an Inlet11. When the target objects are put into the unit body of the annealing unit1through the inlet11and the inlet11is closed, the unit body is vacuumed (vacuum degree is lower than 1E-3 torr), and then heated to 2000-3000° C., the graphite crucible is purified by removing the gas adsorbed on the graphite crucible and the internal pores of the graphite at high temperature. At the same time, the halogen gas (HCl) can also be introduced into the unit body to eliminate the residue impurities, such as, metal pollutants, but not limited to this, during graphite crucible processing, to reduce polycrystalline generation, stabilize resistivity, and generate high-quality silicon carbide single crystals.

The annealing unit1is provided with a heat exchange device (not shown in the figure), which is used to exchange heat inside and outside the annealing unit1to quickly eliminate the internal high temperature generated by the annealing process. Through special design, the heat exchange device can be integrated with automation equipment, and the sensor will automatically open the door to dissipate heat when the temperature inside the unit body reaches 500° C. The heat exchange device can, for example, guide the heat exchange fluid into the annealing unit1through pipelines to absorb heat and then guide the fluid to the outside. Then, air cooling or liquid cooling can be used to remove the heat absorbed by the heat exchange fluid and then the fluid is guided into the annealing unit1again to absorb heat, and the heat exchange process is carried out in such a cycle.

The atmosphere control unit2is used to connect the annealing unit1and the crystal growth unit3in a closed manner, and includes a gas control system21disposed inside therein. A transport system5is provided for connecting the annealing unit1, the atmosphere control unit2, and the crystal growth unit3, and the transport system5is used to transport the target objects, including the graphite crucible7, silicon carbide seed crystal, and silicon carbide powder after the high-temperature purification through the annealing unit1to the atmosphere control unit2, the silicon carbide seed crystal and silicon carbide powder are then placed into the graphite crucible7in the atmosphere control unit2, and then the thermal insulation material34is used to cover the graphite crucible7to form the container33. The transport system5then transports the container33and other objects to the crystal growth unit3to perform the crystal growth process.

The transport system5includes: a first track51, a second track51′, a third track51″, and a trolley52provided on the first track51, the second track51′, and the third track51″, wherein, the first track51is arranged in the atmosphere control unit2, the second track51′ is arranged in the annealing unit1, and the third track51″ is arranged in the crystal growth unit3. The first track51has a different track gauge from the second track51′ and the third track51″, but the second track51′ has the same track gauge as the third track51″. In the embodiment of the invention shown in the figure, the track gauge P1of the first track51can be smaller than the track gauge P2of the second track51′ and the third track51″, but the track gauge is not limited therein. In actual situations, the track gauge P1of the first track51can be larger than the track gauge P2of the second track51′ and the third track51″ according to practical applications. The two ends of the first track51form a separate, discontinuous “broken track” design because of the different track gauges of the second track51′ and the third track51″. Because different equipments may have different heights, therefore it is beneficial to deploy the annealing unit1, the atmosphere control unit2, and the crystal growth unit3in an environment with a difference in height or other topography. In other words, because the first track51and the second and third tracks51′,51″ are not continuous, the first track51and the second and third tracks51′,51″ can be laid in environments with height differences or other different terrains, thereby increasing the flexibility of the location of the crystal growth device.

The trolley52has a plurality of first wheels521that can match the first track51, and a plurality of second wheels522that match the second track51′ and the third track51″, respectively. Specifically, as shownFIG.3andFIG.5, the first wheels521and the second wheels522are arranged in pairs and coaxially below the trolley52, and the wheel distance of each pair of coaxial first wheels521is smaller than that of each coaxial second roller522. The wheel distance of every coaxial pair of first wheels521is equal to the track gauge of the first track51, and the wheel distance of every coaxial pair of second wheels522is equal to the track gauge of the second track51′ and the third track52″. Accordingly, when the trolley52is located in the atmosphere control unit2, the first wheels521roll on the first track51, and the second wheels522are suspended; when the trolley52moves from the atmosphere control unit2to the annealing unit2, the second wheels522roll on the second track51′, and the first wheels521are suspended; and when the trolley52moves from the atmosphere control unit2to the crystal growth unit3, the second wheels522roll on the third track51″ (as shown inFIGS.4and6), and the first wheels521are suspended; when the trolley52moves from the annealing unit1or the crystal growth unit3to the atmosphere control unit2, the first wheels521run on the first track51, and the second wheels522are suspended. As such, the track switching of the trolley52among the annealing unit1, the atmosphere control unit2, and the crystal growth unit3can run smoothly.

The gas control system21can control the content of water, oxygen, and nitrogen in the atmosphere control unit2. Preferably, the content of water, oxygen, and nitrogen is lower than 100 ppm, ideally 10 ppm-1 ppb, and inert gases, such as Argon, can be used to provide the cleanliness of the environment in the atmosphere control unit2, and to prevent the target objects, such as graphite crucibles purified by the annealing unit1, from being polluted inside the atmosphere control unit2. When the gas control system21supplies inert gas, the pressure valve can be used to control the pressure in the atmosphere control unit2to maintain a slightly positive pressure of 760 torr to 770 torr, which is higher than the atmospheric pressure, so as to avoid external air from infiltrating into the atmosphere control unit2to pollute the annealed and purified graphite crucible.

The working platform4is connected to the atmosphere control unit2, to facilitate the staff to operate equipment to install silicon carbide seed crystal and silicon carbide powder into the graphite crucible7and cover the shell-shaped heat-insulating material34. In the practical process of the present invention, the target objects, such as graphite crucibles, silicon carbide seed crystal, and silicon carbide powders, purified by the annealing unit1are transported to the atmosphere control unit2by the trolley52. In such a state, the staff deployed at the working platform4, through the entrance and exit41and the intermediary equipment of a clean environment commonly known as “glove box”, installs the silicon carbide seed crystal on the top of the lid of the graphite crucible7, installs the silicon carbide powder into the graphite crucible, and covers the lid on the graphite crucible, followed by covering with the heat-insulating material34to form the container33. The, the container33is transported to the crystal growth unit3by the trolley52to perform the crystal growth process.

Moreover, a thermal exchange system22can also be provided outside the atmosphere control unit2for exchanging heat between the inside and outside of the atmosphere control unit2to quickly remove the high temperature inside the atmosphere control unit2. The thermal exchange system22can, for example, guide the heat exchange fluid to the atmosphere control unit2through pipelines to absorb heat and then guide the fluid to the outside, and then use air cooling or liquid cooling to remove the heat absorbed by the heat exchange fluid and then guide the fluid to enter the atmosphere control unit2again to absorb heat, so that the heat exchange process is carried cyclically.

The crystal growth unit3is a device for carrying out the crystal growth process on the silicon carbide seed crystal and silicon carbide powder installed into the graphite crucible7of the container33. The crystal growth unit3has an outlet31for taking out the container33and the crystal that have completed the crystal growth process. More specifically, as shown in FIGS.1and2, the crystal growth unit3includes a lifting mechanism32positioned below and a crystal growth furnace positioned above. The lifting mechanism32comprises a driving device321and a first plate positioned at the top end of the driving device321. The driving device321can be, for example, a screw cylinder, a pneumatic cylinder or an oil hydraulic cylinder, and is used to vertically transport the first plate61into or out of the chamber of the crystal growth furnace. More specifically, after the silicon carbide seed crystal and silicon carbide powder are installed in the atmosphere control unit2in the graphite crucible7and covered with the thermal insulation material34, they are then transported to the crystal growth unit3by the trolley52, and are placed in the crystal growth unit3through the aforementioned trolley or mechanical arm (not shown in the figure) on the track of the “broken track” design for transferring the container33to the first plate61, and then the first plate61and the container33carried thereon will be lifted by the lifting mechanism32to move up into the chamber of the crystal growth furnace, and the crystal growth process begins after the outlet31and related inlets and outlets are closed. After the crystal growth process is completed, when the temperature drops to an appropriate temperature, the outlet31is opened to remove the container33and take out the crystal.

In addition, as shown inFIG.7, the present invention can also dispose the first weighing system6in the crystal growth unit3to detect the micro weight change of the container33in the crystal growth process (the variation range of detection can be 0.01 g˜100 g). The quality of crystal growth can be judged by recording the weight change of the container33along the crystal growth time axis, so as to judge the abnormal situation of the process in advance, and thereby the engineers can adjust or correct the process in real time according to the situation. The quality of the product will not be affected simply because the crystal growth process cannot be observed from the outside to see the changes in the internal crystal growth.

Specifically, due to various factors in the growth process of silicon carbide crystals, various factors may cause the grown crystals to partially drop or result in defects, resulting in lighter weight at positions where there are local drops or defects, so that the weight of the container33produces an unbalanced fluctuation phenomenon at the moment when the crystal generates a defect, for example, the crystal is tilted and causes uneven weight, or the moment when part of the material of the crystal falls to the graphite crucible7of the container33to cause weight changes, etc. Therefore, as shown inFIG.7, the present invention arranges the first weighing system6on the first plate61to sense the weight of the thermal insulation material34and the graphite crucible7of the weight of the container33carried on the first plate61. For example, the first weighing system6can distribute a plurality of first weight sensors62along the periphery of the first plate61, an extension tube63extends from the center of the first plate61, and the first plate61extends to the outside of the crystal growth unit3through the extension tube63. The first weight sensors62are connected by wires64and the wires64pass through the extension tube63to be electrically connected to the computer system. In addition, the appropriate position of the extension tube is also provided with an infrared pyrometer (not shown). The infrared pyrometer is electrically connected to the processing unit of a computer system to sense the temperature at the bottom of the graphite crucible7after the graphite crucible7inside the container33is heated by a heater9. In one of the embodiments of the present invention, the first plate61can be a disc, and a plurality of first weight sensors62are equiangularly distributed along the circumference of the first plate61(as shown inFIG.8). In another embodiment, the first plate61can be a disc, and a plurality of first weight sensors62are equiangularly and radially distributed along the circumference of the plate (as shown inFIG.9). The quantity and distribution density of the first weight sensor62can be changed according to actual needs. When the quantity and density are higher, the more weight change positions can be detected, and the detection is more precise. By arranging the first weight sensors62equiangularly on the first plate61, the position of abnormal weight can be detected more evenly. Accordingly, when the crystal8grows downward from the lid71at the upper end of the graphite crucible7, a local crystal drop or defect occurrence will cause the weight fluctuation of the container33at the corresponding position, thereby the first weight sensor62at the position adjacent to the drop or defect will immediately detect that the weight of this position is different from other positions (the detection fluctuation range can reach 0.01 g-100 g), and then convert the relevant data into digital data and send to the computer system to be processed by the processing unit and stored and recorded by the storage unit. Hence, relevant process engineers can make timely process adjustments or corrections based on the detected relevant information and data, avoiding unnecessary waste of process time, thereby reducing manufacturing costs.

In another embodiment of the present invention, a second weighing system6′ (as shown inFIG.2) can also be disposed in the annealing unit1to detect the micro weight change of target objects, such as, graphite crucible, silicon carbide seed crystal and silicon carbide powder during the annealing process, and the detection range can be 0.01 g-100 g. The annealing quality can be judged by recording the weight change of these target objects after the impurities are removed during the annealing process, so as to judge the abnormal situation of the process in advance; thereby, the engineering personnel can adjust or correct the annealing process in real time according to the situation.

Specifically, since the target objects, such as, graphite crucible, silicon carbide seed crystal, and silicon carbide powder, may not be purified due to various factors during the annealing process, the impurities may not be removed in some positions and the weight is heavier than other positions. Therefore, in the present invention, the second weighing system6′ can be arranged under the second plate61′ inside the annealing unit1to sense the weight of the graphite crucible7, silicon carbide seed crystal and silicon carbide powder. The second weighing system6′ has the same structure as the first weighing system6, so the description will be made with reference toFIG.7-9, that is, the second weighing system6′ may include a second plate61′, and a plurality of second weight sensors62′ are distributed around the second plate61′. An extension tube63extends from the center of the second plate61′, and the second plate61′ extends through the extension tube63to the outside of the annealing unit1. The second weight sensors62′ are connected through wires64and the wires64passed through the extension tube63, and then electrically connected to the processing unit of the computer system. Likewise, the second plate61′ can be a disc, and a plurality of second weight sensors62′ are equiangularly distributed along the circumference of the second plate61′ (as shown inFIG.8), or the plurality of second weight sensors62′ are equiangularly and radially distributed along the circumference of the second disc61′ (as shown inFIG.9). The number and distribution density of the second weight sensors62′ can be changed according to actual needs. When the quantity and density are higher, the more weight change positions can be detected, and the detection is more precise. Moreover, by disposing the second weight sensor62′ equiangularly around the second plate61′, the position of abnormal weight can be detected more evenly. Accordingly, when the weight of the target object containing the graphite crucible7fluctuates during the annealing process because the impurities in some positions cannot be removed, the second weight sensor62′ corresponding to or close to the position can immediately detect, and the detected fluctuation range can reach 0.01 g-100 g. The relevant data is converted into digital data and then sent to the processing unit of the computer system for processing, and stored and recorded by the storage unit. Hence, relevant process engineers can make timely process adjustments or corrections based on the detected relevant information and data, avoiding unnecessary waste of process time, thereby reducing manufacturing costs.

The above examples only express the preferred implementation of the present invention, and its description is more specific and detailed, but it cannot be interpreted as a limitation of the patent scope of the present invention. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.