KR101292001B1 - Method for drying silicon sludge - Google Patents

Abstract

PURPOSE: A silicone sludge drying method is provided to recycle silicone sludge generated during semiconductor and solar wafer processing processes using a microwave drying method. CONSTITUTION: A silicone sludge drying method is as follows. A conveyor belt (140) sends silicone sludge to a microwave drying chamber (110). The silicone sludge is heated in the microwave drying chamber at a temperature of 40-100 degrees using microwaves to remove oil from the silicone sludge. The silicone sludge comprises silicone and 50-80 weight% of SiC. The conveyor belt is a mesh belt composed of mesh apertures. [Reference numerals] (116) O2 sensor; (120) Controller

Description

Method for drying Silicon Sludge

The present invention relates to a method for drying silicon sludge which is a by-product generated during silicon wafer cutting, and more particularly, to a method for removing oil contained in silicon waste sludge using microwave drying.

Silicon, widely used as a wafer in the solar cell and semiconductor industries, is sliced from a silicon ingot into a wafer using a wire saw. In the cutting, an abrasive slurry containing silicon carbide having an average particle diameter of about 10 microns is used, and as a result, abrasive sludge containing silicon carbide and other oxides containing silicon carbide as a main component is produced.

In the past, silicon sludge has been landfilled by waste disposal companies, but recently, there have been attempts to recover a large amount of material such as silicon or silicon carbide contained in silicon sludge.

Representative techniques for recycling conventional silicon sludge include polishing slurry regeneration techniques, solids separation recovery techniques, and silicon carbide synthesis techniques.

For example, Korean Laid-Open Patent Publication No. 2003-84528 discloses reaction of a non-ionic surfactant in a waste slurry with a weight ratio of 1 to 20% and alcohol or solvent for 5 to 50% for a predetermined time (5 minutes to 10 hours or more). After the separation, the same minerals are formed in layers by centrifugal separators, and the layers are separated.Then, the oils are separated and put into separate containers using an oil pump for each layer, and then dried using a dryer (by product use) as needed. After this, it introduces the technology to separate and recycle by size by passing the classifier as needed.

In addition, Korean Patent Laid-Open Publication No. 2004-55218 separates solids such as silicon, silicon carbide, copper, and iron by filtering waste slurries, and removes copper and iron powder using specific gravity screening and magnetic screening, and at room temperature. Hydrochloric acid is pickled at a solid solution concentration of 30% to obtain a silicon and silicon carbide mixed powder, which is mixed with graphite powder to produce a silicon carbide composite by silicon carbide at 1600 ° C or higher. Subsequently, after the crushing of the manufactured silicon carbide composite, a secondary treatment process for removing impurities is performed to obtain silicon carbide of high purity.

However, this method has a problem in that an excessive treatment process is applied to the separation and recovery of sludge solids, thereby obscuring the original intention of manufacturing silicon carbide from cheap silicon waste sludge, and in order to manufacture silicon carbide sintered body, There is also a problem that the molding and sintering process must be applied again with carbide powder.

Meanwhile, Korean Patent Publication No. 2011-60701 discloses a method of manufacturing silicon carbide sintered body by heat-treating the silicon sludge to remove oil, and mixing and molding a carbon source into silicon sludge to react and sinter in a non-oxidizing atmosphere at 1300 to 1900 ° C. Presenting.

However, the disclosed patent is an example of a process for removing oil by heat treating silicon sludge, and applying a degreasing process at a temperature of 100 to 600 ° C., preferably at 300 ° C., in which part of the surface of the silicon powder is oxidized. Trace amounts of surface silicon oxide are the cause of the silicon carbide production reaction to occur at higher temperatures.

Korean Laid-Open Patent No. 2011-60701 Korean Patent Publication No. 2004-55218 Korean Laid-Open Patent No. 2003-84528

In order to solve the above problems of the prior art, the present invention provides a method for removing the oil contained in the silicon waste sludge using microwave drying to recycle the silicon waste sludge generated in the semiconductor and solar wafer processing process. For the purpose of

In order to achieve the above technical problem, the present invention comprises the steps of introducing a silicon sludge containing silicon and SiC and a liquid component content of 20 to 50% by weight into a microwave drying chamber by a conveyor belt; And it provides a silicon sludge removal method comprising the step of removing the oil by microwave heat treatment to the silicon sludge at a temperature of 40 ~ 100 ℃ in an inert atmosphere in the microwave drying chamber.

In the present invention, the SiC content of the silicon sludge is preferably 50 to 80% by weight.

In the present invention, the conveyor belt is preferably a mesh belt.

In the present invention, the horizontal and vertical sizes of each mesh constituting the mesh belt are preferably in the range of 1 mm to 4 mm.

In the present invention, the mesh belt is preferably a glass fiber mesh belt.

In the present invention, the mesh belt is preferably a Teflon coated glass fiber mesh belt.

In the present invention, the microwave irradiation time is preferably 10 to 30 minutes.

According to the present invention, there is an advantage that the oil contained in the silicon waste sludge can be removed in a state where the oxidation of silicon contained in the silicon solid content is suppressed as much as possible by microwave heating in a very short time.

1 is a view schematically showing the configuration of a microwave dryer according to a preferred embodiment of the present invention.
2 is a view schematically showing the configuration of the conveyor belt of FIG.
2 is a graph showing the results of the FT-IR analysis of the microwave dried sludge solids according to a preferred embodiment of the present invention.

Hereinafter, the present invention will be described in detail through preferred embodiments of the present invention.

The silicon slurry drying process of the present invention comprises a process of introducing silicon sludge into the conveyor belt and an oil removal process.

First, the silicon sludge collected at the wafer processing plant is introduced into a conveyor belt. At this time, the silicon sludge is composed of a liquid component and a solid content, the solid content contains a small amount of impurities.

Table 1 is an analysis table analyzing the components of the solid impurities contained in the silicon sludge as a by-product of the silicon sludge cutting process.

Na
(mg / kg) K
(mg / kg) Ca
(mg / kg) Zn
(mg / kg) Fe
(mg / kg) Al
(mg / kg) Cu
(mg / kg) 4 12 101 87 8,250 25 205

Thus, it can be seen that the silicon sludge contains a trace amount of alkali metal or metal element, of which Fe and Cu are derived from the cutting device.

Except trace impurities, silicon sludge consists of liquid component oil, solid component silicon and SiC powder. Oil and SiC are derived from the cutting oil and the cutting substrate during the cutting process. The oil is generally made of a polymer such as ethylene glycol (EG) or polyethylene glycol glycol (PEG), diethylene glycol (DEG).

In the present invention, the silicon and SiC content of the silicon sludge varies depending on the source of the waste sludge. In the present invention, the SiC contained in the silicon sludge functions as a microwave absorbing material. Therefore, the SiC content in the silicon sludge of the present invention is preferably 50 to 80% by weight. Therefore, waste sludge having two or more different SiC contents may be mixed and blended so that the SiC content is 50% by weight or more. Of course, alternatively, SiC powder prepared separately may be mixed in the sludge solids.

In addition, the content of the liquid component (for example, oil) in the silicon sludge is preferably 20 to 50% by weight, because if the content of the liquid component is less than 20% by weight smoothly discharged from the hopper (Hopper) If the liquid content is more than 50% by weight, the amount of microwave absorption in the silicon and SiC powders serving as the microwave absorbing material in the silicon sludge is not achieved. This is because there is less and the removal efficiency of the said oil falls.

Silicon sludge introduced into the conveyor belt is subjected to oil removal in a microwave dryer.

1 is a view schematically showing the configuration of a microwave dryer applicable to the present invention, Figure 2 is a view schematically showing the configuration of the conveyor belt of FIG.

As shown in FIG. 1, the microwave dryer may include a microwave drying chamber 110, a controller 120, an inert gas source 130, and a conveyor belt 140.

In the present invention, the controller 120 may control a drying condition including a temperature and an atmosphere in the microwave drying chamber 110.

The microwave drying chamber 110 may be provided with a magnetron 112, a temperature sensor 114, and an oxygen sensor 116 for adjusting drying conditions.

In this case, the reaction volume of the microwave drying chamber 110 may increase linearly according to the capacity of the magnetron 112 located at an appropriate position in the microwave drying chamber 110. Increasing the magnetron capacity in (110) can increase the dosage of silicon sludge and consequently increase the amount of oil separation from the silicon sludge.

In addition, in the present invention, at least one magnetron having a capacity of 1 kW may be located in consideration of the input amount of silicon sludge at an appropriate location in the microwave drying chamber 110. As described above, two or more magnetrons having a capacity of 1 kW may be used as the micro The reason for the installation at the proper place in the wave drying chamber 110 is to secure the economics of the microwave dryer by using the magnetron of 1 kW capacity because the cost is high for the 3 kW or 5 kW magnetron. To handle sludge 45g / h, 12 magnetrons with 1kW capacity are required.)

In addition, a plurality of temperature sensors 114 may be provided to control the temperature in the chamber within an appropriate range, and a plurality of oxygen sensors 116 may also be provided.

The controller 120 controls the operation of the magnetron 112. The controller 120 allows the internal temperature of the chamber to be maintained within an appropriate temperature range from the temperature data measured by the temperature sensor 112. As can be seen through the embodiment of the present invention to be described later, the irradiation time of the microwave is 10 to 30 minutes, the internal temperature of the microwave drying chamber 112, for example, the microwave inner wall surface temperature is preferably 40 ~ It is preferable to maintain at 100 ℃, in this case the surface temperature of the solid phase (eg, silicon and SiC powder) and the liquid phase (eg, oil) of the silicon sludge in the microwave drying chamber 112 is 300 ~ 500 It may be maintained at ℃.

In addition, in the present invention, the controller 120 may control a gas atmosphere inside the microwave drying chamber 110. This control operation may be performed by controlling the supply gas flow rate of the inert gas supply source 130 from the oxygen concentration measured by the oxygen sensor 114 or the like inside the microwave drying chamber 110. In addition, in the present invention, preferably, nitrogen gas or argon gas may be used as the gas source of the inert gas source 130, and microwave drying is performed to prevent combustion of DEG or PEG, which is a main component of oil, and oxidation of silicon. The oxygen concentration in the chamber 110 is preferably 1 to 5 vol% or less.

In the present invention, the microwave drying chamber 110 is maintained in a non-oxidizing atmosphere, such as an inert atmosphere. Inert atmosphere in the present invention to suppress the risk of ignition in the microwave drying chamber 110 and at the same time to suppress the oxidation of the silicon powder and deformation of the oil during the degreasing process. Oxidation of the silicon powder causes a carbonization reaction of silicon by a so-called Acheson reaction and thus has a problem of increasing the carbonization reaction temperature. However, in the present invention, the oxidation of silicon contained in the sludge solid content is suppressed as much as possible by the microwave treatment for a very short time.

The microwaves irradiated in the microwave drying chamber 110 are selectively absorbed by the microwave absorbing material such as SiC in the sludge. As a result, the surface of the microwave absorbing material in the sludge rises rapidly to a high temperature, and the oil contained in the sludge is vaporized. The process of vaporizing the oil by microwave absorption occurs uniformly on the surface of the microwave absorbent material in the sludge and can be performed in a very short time. Therefore, the possibility of the silicon powder contained in the silicon sludge in contact with oxygen is further reduced and the oxidation potential of silicon is very low.

The conveyor belt 140 is disposed below the microwave drying chamber 110 to sequentially introduce the silicon sludge into the microwave drying chamber 110.

At this time, the conveyor belt 140 is preferably a mesh belt as shown in Figure 2, the reason for configuring the conveyor belt 140 as a mesh belt as described above is the micro-in the microwave drying chamber 110 This is to allow the oil removed from the silicon sludge by heat treatment to be discharged downward through the microwave drying chamber 110 through the mesh belt.

In addition, as shown in FIG. 2, the horizontal and vertical sizes of the apertures of the respective meshes constituting the mesh belt are preferably 1 mm to 4 mm. In principle, the aperture size of the mesh in the present invention may be designed in consideration of the proper discharge of the evaporated fraction and the size of the sludge solids. However, the dried silicone sludge exhibits a property of sticking to the mesh fiber, and thus it is possible to use a mesh exceeding the size of the sludge solids. According to the present invention it was possible to provide good breathability without leaving the solids in the mesh of about 4 * 4 mm size.

In addition, the mesh belt may be a glass fiber mesh belt. The reason why the mesh belt is composed of a glass fiber mesh belt as described above is that the silicon, SiC, and oil in the silicon sludge have a surface temperature of 300 to 500 ° C. in the drying process of the silicon sludge by microwave heating. This is to have sufficient heat resistance to cope with. More preferably, the mesh belt may be Teflon coated. Teflon coating may prevent degradation of the glass fiber to compensate for heat resistance and durability.

It will be appreciated by those skilled in the art that the microwave dryer described above may be implemented in a batch or continuous manner.

The mixture dried using the microwave may be converted to SiC at a low temperature because the oxidation of silicon is suppressed.

In the case of the dried silicon slurry according to the present invention, the carbon carbide is mixed at a low temperature of 1300 ° C. or less after being mixed with a carbon source. This is due to the absence of surface oxides of silicon contained in the silicon sludge of the present invention.

Conventionally, in the case of producing SiC by sintering silicon, the reaction sintering temperature is generally performed at a temperature of 1450 ° C or higher. However, since the melting point of pure silicon is 1412 ° C, silicon cannot maintain a skeleton at such sintering temperatures. Therefore, a silicon carbide sintered body is obtained by means of first forming a preform with a molded body made of SiC and / or a carbon source, and then immersing the formed preform in molten silicon melt. However, this conventional silicon carbide sintered body manufacturing process is very complicated and expensive.

In the present invention, the silicon carbide sintered body which maintains the molding shape can be manufactured even though the molded product is prepared by mixing the silicon sludge and the carbon source without a separate preform. This is because the residual oil contained in the silicon sludge is formed evenly on the surface of the silicon powder, and the carbonization reaction is preceded at a temperature lower than the melting point of the silicon.

≪ Example 1 >

The solids were recovered by centrifuging the silicon sludge obtained from the domestic semiconductor wafer processing plant. The centrifuged silicon sludge solids content is shown in Table 2. In addition, the content of the liquid component (oil) contained in the sludge solid content was 40% by weight.

division Si SiC impurities weight% 21.7 70.0 8.3

The obtained sludge solids were charged into a continuous microwave drying chamber as shown in Figs. 1 and 2, and the residence time (i.e. microwave irradiation time) inside the chamber was adjusted so that the temperature of the inner wall of the microwave drying chamber was 40 deg. , And maintained at 80 ° C, 100 ° C, and 150 ° C.

In addition, nitrogen gas was flowed into the chamber to maintain the nitrogen atmosphere. The sludge solids were dried for 10 to 40 minutes in the chamber, and the SiO ₂ content for each temperature is shown in Table 3.

Temperature SiO ₂ content Survey time 40 ° C 0.4 10 minutes 80 ° C 0.5 20 minutes 100 ° C 0.6 30 minutes 150 ° C 4.0 40 minutes

As can be seen in Table 3, when the temperature of the inner wall of the microwave drying chamber is 40 ℃ ~ 100 ℃, the irradiation time of the microwave 10 minutes to 30 minutes, the oxidation of silicon hardly proceeds, the Si0 ₂ content change It could be confirmed that there is almost no.

The dried solids were also analyzed by FT-IR. Figure 2 is a graph showing the results of the FT-IR analysis of the solid dried at 80 ℃ in accordance with the present invention. For comparison with the present invention, the results of the FT-IR analysis of the sludge solids heat treated in the conventional rotary rotary furnace are also shown.

Referring to FIG. 3, the Si-O band of the microwave dried solid component (a) at 80 ° C. shows very small values. On the other hand, it can be seen that the sludge solids heat-treated in the conventional rotary rotary furnace exhibits a very high Si-O band value.

<Example 2>

The dried sludge solids were mixed with carbon black with a particle size of 0.5 micron. At this time, the content of the carbon black was such that the molar ratio with silicon is 1: 1.

The prepared mixed powder was heat-treated at 900 to 1300 ° C. for 1 hour at different temperatures in a vacuum atmosphere to synthesize silicon carbide powder. At this time, the temperature increase rate at the time of sintering was 10 degree-C / min. The obtained synthetic powder was analyzed by chemical composition to measure the residual Si content.

Table 4 below shows the residual silicon content at each heat treatment temperature.

Heat treatment temperature (° C) 900 1000 1200 1300 Residual Si Content (wt%) 15.0 11.2 4.3 1.5

As can be seen in Table 4 above, it can be seen that there is almost no residual silicon at a temperature of 1300 ℃. Therefore, according to the present invention, it is possible to synthesize SiC powder at a temperature much lower than the melting temperature of Si.

&Lt; Comparative Example 1 &

Sludge solids similar to those of Example 1 were dried in a microwave dryer. However, by changing the residence time in the microwave dryer (ie microwave irradiation time), the temperature inside the micro dryer was dried until it reached 150 ° C. At this time, the residence time was 40 minutes. As in Example 2, carbon black was mixed with the dried sludge solid to synthesize silicon carbide powder at a temperature of 1200 to 1500 ° C (?). Table 5 below shows the results of measuring the residual Si content of the powder after the synthesis process.

Microwave
Reactor temperature (° C) Residual Si Content by Heat Treatment Temperature (%) 1200 ° C 1300 ° C 1400 ° C 1500 ° C 150 12.4 7.3 3.2 0.5

As can be seen from the above table, it can be seen that a considerable amount of Si remains at a synthesis temperature of 1200 ° C. as the drying temperature increases, and it can be seen that a temperature of 1400 ° C. or more is required for the synthesis of complete SiC.

&Lt; Example 3 >

Unlike Example 1, the correlation between the SiC content in the sludge solids and the drying conditions was analyzed. At this time, the drying conditions were controlled by the microwave irradiation time, in each case the irradiation time was limited in the range that the chamber inner wall temperature does not exceed 100 ℃.

The content of the residual liquid component in the sludge solids after each drying condition was measured. At this time, the content of the residual liquid component was measured using a weight loss when maintained at 500 ℃ for 1 hour. Table 6 below is a graph summarizing the liquid content of the sludge content and drying conditions.

Sludge
SiC content Residue in sludge with microwave dryer residence time
Liquid content (%) 5 minutes 10 minutes 15 minutes 30 minutes 40 32% 28% 22% 10% 60 8% 3% Tr Tr 80 5% Tr Tr Tr

As can be seen from the table above, in the case of 40 wt% of the SiC content, 10 wt% of the liquid component remains in 30 minutes of microwave irradiation, but the liquid component content of 10 minutes or less as the SiC content in the sludge increases. It can be seen that can be maintained at less than 10% by weight even with a short irradiation time.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Accordingly, the embodiments described in the present invention are not intended to limit the technical spirit of the present invention but to describe the technical spirit of the present invention. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

100 microwave dryer 110 chamber
112 magnetron 114 temperature sensor
116 oxygen sensor 120 controller
130 Inert gas source 140 Conveyor belt

Claims (7)

Introducing a silicon sludge containing silicon and SiC and having a liquid component content of 20 to 50% by weight into a microwave drying chamber by a conveyor belt; And
And a drying step of removing the oil by microwave heating the silicon sludge at a temperature of 40 to 100 ° C. in an inert atmosphere in the microwave drying chamber. The method of claim 1,
SiC content of the silicon sludge drying method, characterized in that 50 to 80% by weight. The method of claim 1,
The conveyor belt is a silicone sludge drying method, characterized in that the mesh belt. The method of claim 3,
Horizontal and vertical size of each mesh aperture constituting the mesh belt is characterized in that the silicone sludge drying method characterized in that the range of 1mm ~ 4mm. The method of claim 3,
And the mesh belt is a glass fiber mesh belt. The method of claim 3,
Wherein said mesh belt is a Teflon coated glass fiber mesh belt. The method of claim 1,
Silicon sludge drying method characterized in that the irradiation time of the microwave in the drying step is 10 ~ 30 minutes.

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