Method for manufacturing silicon nitride substrate and silicon nitride substrate manufactured using the same

Abstract

A method for manufacturing a silicon nitride substrate is provided. The method for manufacturing a silicon nitride substrate according to an embodiment of the present invention includes the steps of: preparing a ceramic composition including a metal silicon powder and a crystal phase control powder including a rare earth element-containing compound and a magnesium-containing compound; preparing a sheet-shaped molded body from the prepared slurry by mixing the ceramic composition with a solvent and an organic binder; and heat treating the molded body including a nitriding section in which heat is treated at a first temperature in the range of 1300 to 1500°C while nitrogen gas is applied at a predetermined pressure, and a sintering section in which heat is treated at a second temperature in the range of 1700 to 1900°C. This allows for a reduction in manufacturing time and man-hours compared to the conventional method, making it suitable for mass production. In addition, the silicon nitride substrate has excellent mechanical strength because melting and dissolution of silicon during the nitriding process is minimized or prevented. Furthermore, by entering the sintering section while suppressing abrupt transition to the beta phase, and then completing sintering, transition to the beta phase, promotion of growth of the beta phase, and uniform growth are possible, and the substrate has improved thermal conductivity. Furthermore, since the thermal conductivity and mechanical strength are uniform regardless of the position of the substrate, a substrate of higher quality can be realized.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a silicon nitride substrate and a silicon nitride substrate produced using the same. [Background technology]

[0002] Silicon nitride sintered bodies have excellent wear resistance, heat resistance, low thermal expansion, thermal shock resistance, and corrosion resistance to metals, and have traditionally been used in a variety of structural components, such as gas turbine components, engine components, steelmaking machine components, etc. In addition, due to their high insulating properties and good heat dissipation properties, they are used as materials for electrical components, such as ceramic substrates.

[0003] Silicon nitride substrates have traditionally been manufactured using a two-step process: producing silicon nitride powder and then sintering the produced silicon nitride powder. The reason for this process is that it is difficult to create a substrate that exhibits uniform physical properties regardless of position during nitriding and sintering in substrate form. To solve this problem, the method of first producing silicon nitride powder to have uniform physical properties in powder form and then using this to manufacture substrates has been widely used.

[0004] However, in the two-step method described above, after nitriding, the nitride body must be cooled and crushed, and then molded and sintered to obtain the desired shape, which requires a manufacturing time of 50 hours or more, and there is a risk of increasing the number of steps.

[0005] This dramatically reduces manufacturing time and man-hours, and the resulting silicon nitride substrate has excellent thermal conductivity and mechanical strength. At the same time, there is an urgent need to research a method for manufacturing a silicon nitride substrate that exhibits these physical properties uniformly across the substrate. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for manufacturing a silicon nitride substrate, which can manufacture a silicon nitride substrate with reduced manufacturing time and man-hours compared to conventional methods for manufacturing a silicon nitride substrate, and which has excellent flatness, thermal conductivity, and mechanical strength, and in which these physical properties are uniformly expressed across the substrate, and a silicon nitride substrate manufactured using the same. [Means for solving the problem]

[0007] The present invention has been made in view of the above points and provides a method for manufacturing a silicon nitride (Si3N4) substrate, the method including: preparing a ceramic composition containing a metal silicon powder and a crystalline phase control powder containing a rare earth element-containing compound and a magnesium-containing compound; mixing the ceramic composition with a solvent and an organic binder to prepare a slurry and producing a sheet-shaped molded body from the prepared slurry; and a heat treatment step including a nitriding step in which the molded body is heat-treated at a first temperature in the range of 1300 to 1500°C while nitrogen gas is applied at a predetermined pressure, and a sintering step in which the molded body is heat-treated at a second temperature in the range of 1700 to 1900°C.

[0008] According to an embodiment of the present invention, the metallurgical silicon powder may be obtained by dry-milling polycrystalline metallurgical silicon scraps or single-crystalline silicon wafer scraps to minimize contamination with metal impurities during milling.

[0009] The metal silicon powder may have a resistivity of 1 to 100 Ω·cm.

[0010] The polycrystalline silicon metal scrap or the single crystal silicon wafer scrap may have a purity of 99% or more.

[0011] The rare earth element-containing compound may be yttrium oxide, and the magnesium-containing compound may be magnesium oxide, and the ceramic composition may contain 2 to 5 mol % of the yttrium oxide and 2 to 10 mol % of the magnesium oxide.

[0012] The metal silicon powder may have an average particle size of 0.5 to 4 μm, the rare earth element-containing compound powder may have an average particle size of 0.1 to 1 μm, and the magnesium-containing compound powder may have an average particle size of 0.1 to 1 μm.

[0013] Also, the heat treatment step may be performed continuously from the nitriding section to the sintering section.

[0014] Furthermore, a section in which heat treatment is performed at a temperature lower than the first temperature or cooling is performed to a temperature lower than the first temperature may not be included between the nitriding section and the sintering section.

[0015] The heat treatment may be performed from 1000±20° C. to the first temperature at a temperature increase rate of 0.1 to 2° C. / min while supplying nitrogen gas at a pressure of 0.1 to 0.2 MPa.

[0016] In addition, nitrogen gas can be added at a pressure of 0.1 to 0.2 MPa during the nitriding section, and the nitriding section can be continued for 2 to 10 hours.

[0017] Also, the pressure of the nitrogen gas applied from 1000±20° C. to the first temperature may be lower than the pressure of the nitrogen gas applied in the nitriding section.

[0018] In addition, between the nitriding section and the sintering section, the process may further include a first contraction section in which the temperature is increased from the first temperature to 1700±20°C at a rate of 0.1 to 10.0°C / min under a nitrogen gas pressure of 0.15 to 0.3 MPa, and a second contraction section in which the temperature is increased from 1700±20°C to the second temperature at a rate of 1 to 10°C / min under a nitrogen gas pressure of 0.8 to 0.98 MPa.

[0019] The present invention also provides a silicon nitride substrate manufactured using the manufacturing method of the present invention, which has a thermal conductivity of 75 W / mK or more and a three-point bending strength of 700 MPa or more. [Effects of the Invention]

[0020] The method for manufacturing a silicon nitride substrate according to the present invention reduces manufacturing time and man-hours compared to conventional methods, making it suitable for mass production. Furthermore, the silicon nitride substrate thus manufactured has excellent mechanical strength by minimizing or preventing melting and dissolution of silicon during the nitriding process. Furthermore, by suppressing a rapid transformation to the beta phase and completing sintering after entering the sintering section, the transformation to the beta phase and the promotion and uniform growth of the beta phase are possible, resulting in improved thermal conductivity. Furthermore, the uniform thermal conductivity and mechanical strength, regardless of the position on the substrate, and excellent flatness allow for the manufacture of a higher quality substrate. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a graph showing the variation of temperature conditions over time during a heat treatment step included in one embodiment of the present invention. [Figure 2] 1A is a schematic cross-sectional view of a state where the stacking state of multiple compacts has been changed by moving or re-evacuating after a nitriding step, compared to before a heat treatment (a) according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention may be embodied in various different forms and is not limited to the embodiments set forth herein.

[0023] A silicon nitride substrate according to one embodiment of the present invention can be manufactured by the following steps: preparing a ceramic composition containing a metal silicon powder and a crystalline phase control powder containing a rare earth element-containing compound and a magnesium-containing compound; mixing the ceramic composition with a solvent and an organic binder to prepare a slurry and then forming a sheet-shaped compact from the prepared slurry; and heat-treating the compact, which includes a nitriding step in which the compact is heat-treated at a first temperature in the range of 1300 to 1500°C while nitrogen gas is applied at a predetermined pressure, and a sintering step in which the compact is heat-treated at a second temperature in the range of 1700 to 1900°C.

[0024] First, the step of producing the ceramic composition will be described.

[0025] The ceramic composition can be produced by mixing a ceramic composition containing metal silicon powder and a crystalline phase control powder containing a rare earth element-containing compound and a magnesium-containing compound.

[0026] The metal silicon powder used as the raw material powder can be any metal silicon powder used to produce silicon nitride powder or silicon nitride molded bodies using a direct nitridation method. For example, the metal silicon powder can be polycrystalline metal silicon scrap or single crystal silicon wafer scrap. The polycrystalline metal silicon scrap can be a by-product of polycrystalline metal silicon used in the manufacture of semiconductor process tools or solar panels. Single crystal silicon wafer scrap is also a by-product of silicon wafer manufacturing. Therefore, using these by-product scraps as the raw material powder can reduce manufacturing costs.

[0027] In addition, the polycrystalline metal silicon scraps or single crystal silicon wafer scraps may have a purity of 99% or more, which may be advantageous in ensuring the thermal conductivity and mechanical strength of the silicon nitride substrate thus formed.

[0028] In addition, the metal silicon powder may have a resistivity of 1 to 100 Ω·cm, which may be advantageous for producing a silicon nitride substrate having the physical properties targeted by the present invention.

[0029] The metallurgical silicon powder used as the raw material powder may be preferably obtained by crushing polycrystalline metallurgical silicon scraps or single-crystalline silicon wafer scraps to a predetermined size. To prevent contaminants, such as metal impurities, from being mixed into the raw material powder during crushing, the crushing may be performed using a dry crushing method, specifically, a dry crushing method such as a disk mill, pin mill, or jet mill. If contaminants are present in the metallurgical silicon powder, an additional cleaning process, such as acid washing, may be required to remove the contaminants, potentially increasing manufacturing time and costs. The average particle size of the crushed metallurgical silicon powder may be 0.5 to 4 μm, more preferably 2 to 4 μm. If the average particle size is less than 0.5 μm, it may be difficult to achieve using a dry crushing method, may increase the possibility of contaminant contamination due to pulverization, and may be difficult to densify during sheet casting. Furthermore, if the average particle size of the metallurgical silicon powder exceeds 4 μm, nitriding may be difficult, resulting in the presence of unnitrided portions, making it difficult to densify the final substrate.

[0030] Silicon nitride, the substrate material, is difficult to sinter into a substrate due to its poor self-diffusion and tendency to thermally decompose at high temperatures, limiting the sintering temperature. This makes it difficult to produce a dense, uniformly nitrided substrate. To overcome these difficulties, remove impurities such as oxygen, and improve the physical properties of the silicon nitride substrate, a ceramic composition containing a crystalline phase control powder mixed with a metal silicon powder is used as the raw material powder. The crystalline phase control powder may be, for example, a rare earth element-containing compound, an alkaline earth metal oxide, or a combination thereof. Specifically, one or more of the following may be used: magnesium oxide (MgO), yttrium oxide (YO), gadolinium oxide (GdO), holmium oxide (HoO), erbium oxide (ErO), ytterbium oxide (YbO), and dysprosium oxide (DyO). However, in the present invention, in order to facilitate sintering and crystal phase control of the silicon nitride substrate, magnesium oxide and yttrium oxide are essentially contained in the crystal phase control powder, and the magnesium oxide and yttrium oxide have the advantage of making the manufactured silicon nitride substrate more dense and having a high density, and of reducing the amount of residual grain boundary phase during sintering, thereby further improving the thermal conductivity of the substrate.

[0031] In addition, the silicon-containing ceramic composition may further contain a strength-enhancing powder containing at least one of iron oxide (FeO) and titanium oxide (TiO) to improve mechanical strength against thermal stress and thermal shock during harsh semiconductor manufacturing processes. Preferably, the strength-enhancing powder may contain both iron oxide and titanium oxide.

[0032] In particular, the heat treatment step described below is performed in one step through continuous heat treatment in a single sintering furnace, rather than in separate furnaces for nitriding and sintering. A combination of magnesium oxide and yttrium oxide, or a combination of magnesium oxide, yttrium oxide, iron oxide, and titanium oxide, is useful for nitriding and sintering metal silicon powder to silicon nitride. That is, rather than performing nitriding and sintering in separate furnaces or nitriding followed by cooling and sintering, a silicon-containing ceramic composition is loaded into a furnace and then nitrided and sintered in a single step. It is not easy to achieve uniform nitriding throughout the compact, without dissolving silicon, and to realize a densified sintered body. However, the crystallization control powder contained in the ceramic composition, or a strength-enhancing powder contained together with the crystallization control powder, is useful for achieving uniform nitriding and realizing a densified sintered body. To this end, the ceramic composition may preferably contain 2 to 5 mol % of yttrium oxide and 2 to 10 mol % (preferably 4 to 8 mol %) of magnesium oxide. Furthermore, when iron oxide and titanium oxide are further contained, the ceramic composition may contain 0.1 to 3 mol% of iron oxide and 1 to 5 mol% of titanium oxide, based on the total molar ratio of the ceramic composition. This allows for improved mechanical strength despite the single-step nitriding-sintering process. If the yttrium oxide content is less than 2 mol%, it is difficult to form a densified substrate during sintering, and oxygen is not easily captured in the grain boundary phase. This increases the amount of dissolved oxygen, resulting in low thermal conductivity and reduced mechanical strength of the sintered substrate. If the yttrium oxide content is more than 5 mol%, the grain boundary phase increases, potentially reducing the thermal conductivity and fracture toughness of the resulting silicon nitride substrate. If the magnesium oxide content is less than 2 mol%, the resulting silicon nitride substrate will have low thermal conductivity and mechanical strength, and silicon may be eluted during nitriding, making it difficult to form a densified substrate. Furthermore, if the magnesium oxide content exceeds 10 mol %, a large amount of magnesium remains at the grain boundaries during sintering, resulting in a substrate with low thermal conductivity, difficulty in sintering, and reduced fracture toughness.If the iron oxide content is less than 0.1 mol % and / or the titanium oxide content is less than 1 mol %, the improvement in mechanical strength is insufficient, and if the iron oxide content is more than 3 mol % and / or the titanium oxide content is more than 5 mol %, the mechanical strength of the sintered body may also be reduced.

[0033] Preferably, the yttrium oxide and magnesium oxide may be contained in the composition in a molar ratio of 1:1.5 to 2.0, which may be more advantageous in achieving the object of the present invention.

[0034] In addition, the rare earth element-containing compound powder may have an average particle size of 0.1 to 1 μm, and the magnesium-containing compound powder may have an average particle size of 0.1 to 1 μm, which may be more advantageous in achieving the object of the present invention.

[0035] Next, the prepared ceramic composition is mixed with a solvent and an organic binder to form a slurry, which is then subjected to a process of manufacturing a sheet-shaped compact.

[0036] The solvent and organic binder may be any known solvent and organic binder used in manufacturing ceramic substrates or ceramic green sheets, without limitation. Specifically, the solvent dissolves the organic binder, disperses the ceramic composition, and adjusts the viscosity. Examples of the solvent include terpineol, dihydroterpineol (DHT), dihydroterpineol acetate (DHTA), butyl carbitol acetate (BCA), ethylene glycol, ethylene, isobutyl alcohol, methyl ethyl ketone, butyl carbitol, texanol (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate), ethyl benzene, isopropyl benzene, cyclohexanone, cyclopentanone, dimethyl sulfoxide, diethyl phthalate, toluene, and mixtures thereof. In this case, the solvent is preferably mixed in an amount of 50 to 100 parts by weight per 100 parts by weight of the ceramic composition. If the content of the solvent is less than 50 parts by weight, the viscosity of the slurry is high, making it difficult to produce a green body, and in particular, to control the thickness of the green body. If the content of the solvent is more than 100 parts by weight, the viscosity of the slurry is too low, making it take a long time to dry and making it difficult to control the thickness of the green body.

[0037] The organic binder functions to bind the ceramic composition in a predetermined shape in the prepared slurry. The organic binder is preferably mixed in an amount of 5 to 20 parts by weight per 100 parts by weight of the ceramic composition. The organic binder may be a cellulose derivative such as ethyl cellulose, methyl cellulose, nitrocellulose, or carboxycellulose, or a polymer resin such as polyvinyl alcohol, acrylic ester, methacrylic ester, or polyvinyl butyral. When a compact is manufactured by a tape casting method, polyvinyl butyral is preferably used as the organic binder.

[0038] The slurry may further contain known substances such as a dispersant and a plasticizer that are contained in slurries for producing a molded body using ceramics, but the present invention is not particularly limited thereto.

[0039] The prepared slurry may be formed into a sheet, and in this case, the slurry may be embodied as a compact by a known forming method, such as, but not limited to, a tape casting method.

[0040] Next, the prepared compact is subjected to a heat treatment step.

[0041] Referring to FIG. 1, the compact is loaded into a sintering furnace and then subjected to a heat treatment step including a nitriding section S3 for converting the compact into silicon nitride (Si3N4) and a sintering section S5 for sintering the nitrided compact. The heat treatment step may further include temperature-raising sections S1 and S2 before the nitriding section S3, a temperature-raising section S4 between the nitriding section S3 and the sintering section S5, and a cooling section S6 after the sintering section S5.

[0042] In the manufacturing process according to the present invention, the heat treatment step includes a nitriding step in which a compact is nitrided to form a silicon nitride compact, and a sintering step in which the nitrided compact is sintered to form a substrate. Conventionally, silicon nitride substrates have typically been produced using a two-step process in which silicon powder is converted into silicon nitride powder and then the silicon nitride powder is used to produce a silicon nitride substrate. However, this two-step process requires additional cooling and pulverizing steps after the silicon nitride powder is produced and before sintering, resulting in a long manufacturing time, increased manufacturing costs, and unsuitable for mass production. Nevertheless, the reason for using this two-step process is that nitriding a small-sized powder phase facilitates the production of silicon nitride powder with more uniform properties, which in turn favors ensuring uniform properties for silicon nitride substrates.

[0043] The present invention deviates from the two-step process that was inevitably adopted in the past to realize a substrate with uniform properties, and instead manufactures a silicon nitride substrate by performing both the nitriding process and the sintering process in a one-step process, which is a heat treatment step. This has enabled the realization of a silicon nitride substrate with uniform properties while drastically shortening the manufacturing time, leading to the present invention.

[0044] The heat treatment step can be performed continuously from the nitriding section to the sintering section without interruption of the heat treatment. In addition, since the nitriding is not performed in a powder phase but a compact formed into the shape of the substrate is nitrided and then sintered, it is not necessary to include a section between the nitriding section and the sintering section in which the heat treatment is performed at a temperature lower than the first temperature or in which the cooling is performed to a temperature lower than the first temperature.

[0045] The sheet-like compact may be heat-treated in the form of a laminate 100 in which a plurality of compacts 1 and 2 are stacked, as shown in FIG. 2(a). For example, the sheet-like compact may be heat-treated in a state in which two or more sheets are stacked. In this case, the laminate 100 may be heat-treated while being disposed between BN plates 10. A release agent, for example, BN powder, may be interposed between the stacked compacts 1 and 2 to minimize or prevent sticking between the compacts 1 and 2 after the heat treatment. In this way, it is unavoidable from the viewpoint of productivity to perform the heat treatment on a plurality of stacked compacts at once. However, if the heat treatment step is performed on multiple compacts and the two steps are not performed consecutively between the nitriding and sintering steps due to reasons such as the movement of the stack due to a change in furnace and / or the evacuation, release, and re-evacuation of the furnace, vibrations occurring during the movement of the stack or changes in air pressure during re-evacuation may prevent the stack from fully maintaining its stacked state prior to the heat treatment. As shown in FIG. 2(b), some or all of the compacts may move randomly horizontally, causing unevenness at the side edges of the stack 100. This may result in warping, in which the edges of the compacts 1 and 2 are bent. Furthermore, warping can lead to an increase in the reject rate due to reduced bending strength and flatness. Therefore, performing the heat treatment step consecutively without the need to move the stacked compacts due to a change in furnace and without the evacuation, release, and re-evacuation of the furnace not only shortens the manufacturing time, but also minimizes or prevents problems such as warping at the edges of the silicon nitride substrate after the heat treatment step, reduced bending strength, and reduced flatness.

[0046] Specifically, the heat treatment step may be described as follows: the prepared compact is placed in a furnace and then heat-treated at a predetermined or variable heating rate until it reaches the nitriding section S3. A debinding step may be performed to remove organic compounds, such as organic binders, from the compact. However, if the organic binder content is low, debinding may be omitted.

[0047] Specifically, the debinding process can be performed by loading the prepared compact into a debinding furnace and heating it from the heat treatment start temperature to 900°C at a predetermined or variable heating rate. The debinding process can be performed in a known atmosphere, such as air and / or nitrogen, and the specific atmosphere can be selected appropriately based on the type and content of the organic binder used. However, taking into account the composition of the compact and the type and content of the organic binder, the debinding process can be preferably performed in air in the temperature range from the heat treatment start temperature to 450°C, and in a nitrogen atmosphere in the temperature range from 450°C to 900°C. This can be advantageous for minimizing or completely removing carbon components remaining in the compact after the debinding process. The heat treatment start temperature can be room temperature, for example, 20°C to 25°C. During the heat treatment, the temperature can be increased at a rate of 2 to 8°C / min up to 450°C, and at a rate of 2 to 8°C / min from 450°C to 900°C, and the rate of increase in temperature up to 450°C and the rate of increase in temperature from 450°C to 900°C may be the same or different.

[0048] After the debinding step, the molded body that has been subjected to the debinding step may be subjected to secondary debinding at 900 to 1000° C. In this case, in the range of 900 to 1000° C., it is preferable to raise the temperature at a low rate of 1 to 10° C. / min, more preferably 1 to 3° C. / min, and the pressure is preferably 0.1 to 0.2 MPa, more preferably 0.14 to 0.17 MPa.

[0049] According to a preferred embodiment of the present invention, the temperature is then raised slowly from a predetermined temperature T1, specifically 1000±20°C, to the first temperature T2 while supplying nitrogen gas at a predetermined pressure. Specifically, the temperature can be raised while supplying nitrogen gas at a pressure of 0.1-0.2 MPa, more preferably 0.14-0.18 MPa. The temperature can also be raised at a rate of 0.1-2.0°C / min, more preferably 0.5-1.0°C / min. If the nitrogen gas pressure is less than 0.1 MPa, nitriding of the compact may not be complete even after nitriding section S3, resulting in the presence of unnitrided portions. Furthermore, if the nitrogen gas pressure exceeds 0.2 MPa, silicon elution may occur, resulting in a decrease in the thermal conductivity and mechanical strength of the substrate. Furthermore, if the temperature is raised from 1000±20°C to the first temperature at a rate of less than 0.1°C / min, the time required for the heat treatment step may be excessively long. Furthermore, if the temperature rise rate exceeds 2.0° C. / min, silicon will dissolve, making it difficult to produce a substrate that is completely nitrided with silicon nitride.

[0050] After the compact is loaded into the furnace, there is no limit to the rate of temperature increase until the temperature reaches, for example, 800°C or less, and the temperature can be increased at a rate of, for example, 4°C / min to 30°C / min according to the temperature increase conditions applied to general silicon substrates or silicon powder nitriding. In this range, the temperature can be increased in an inert gas or nitrogen gas atmosphere.

[0051] Thereafter, heat is continuously applied to raise the temperature to a first temperature T2, and then a nitriding step corresponding to nitriding section S3 is performed in which heat treatment is performed at the first temperature T2 while nitrogen gas is applied at a predetermined pressure. The first temperature T2 may be a predetermined temperature in the range of 1300 to 1500°C, preferably 1400 to 1500°C. If the first temperature T2 is less than 1300°C, nitriding may not occur uniformly. Also, if the first temperature T2 exceeds 1500°C, the β crystal phase is rapidly formed, making it difficult to densify the substrate.

[0052] The nitrogen gas pressure applied in the nitriding section S3 may be 0.1 to 0.2 MPa, more preferably 0.14 to 0.18 MPa. If the nitrogen gas pressure is less than 0.1 MPa, nitriding may not occur completely, resulting in unnitrided areas. If the nitrogen gas pressure exceeds 0.2 MPa, silicon may be eluted during the nitriding process, reducing the thermal conductivity and mechanical strength of the substrate. The nitriding process may last 2 to 10 hours, more preferably 1 to 4 hours. The nitriding process time may be adjusted appropriately by adjusting the first temperature T2.

[0053] Furthermore, according to one embodiment of the present invention, the pressure of the nitrogen gas applied from 1000±20°C to the first temperature may be lower than the pressure of the nitrogen gas applied in the nitriding section, which may be advantageous for more uniform nitriding and realizing a substrate with excellent appearance and mechanical strength.

[0054] Furthermore, after the nitriding process, a heat treatment can be performed at a predetermined temperature increase rate up to the second temperature T3, where the sintering process is performed. According to a preferred embodiment of the present invention, the temperature can be increased slowly from the first temperature T2 to the second temperature T3 while supplying nitrogen gas at a predetermined pressure. Specifically, the temperature can be increased at a rate of 0.1 to 10.0°C / min under nitrogen gas at a pressure of 0.1 to 1.0 MPa. If the nitrogen gas pressure is less than 0.1 MPa, it is difficult to suppress the decomposition of silicon nitride. If the nitrogen gas pressure exceeds 1.0 MPa, the pressure resistance of the furnace becomes an issue. If the temperature increase rate from the first temperature T2 is less than 0.1°C / min, the required time for the heat treatment step can be excessively extended. If the temperature increase rate exceeds 10.0°C / min, a rapid transition to the beta phase occurs, which can lead to uneven growth of beta phase crystals, making it difficult to control the crystal structure, and the resulting substrate cannot have the desired physical properties.

[0055] According to an embodiment of the present invention, the temperature increasing section from the first temperature T2 to the second temperature T3 may be divided into two sections, thereby manufacturing a substrate with better physical properties.

[0056] Specifically, between the nitriding section and the sintering section, there may be further included a first contraction section in which the temperature is increased from a first temperature T2 to 1700±20°C at a rate of 0.1 to 10.0°C / min under a nitrogen gas pressure of 0.15 to 0.3 MPa, and a second contraction section in which the temperature is increased from 1700±20°C to a second temperature T3 at a rate of 1 to 10°C / min under a nitrogen gas pressure of 0.8 to 0.98 MPa.

[0057] In this case, the nitrogen gas pressure in the first contraction section may be 0.15 to 0.3 MPa, and the nitrogen gas pressure in the second contraction section may be 0.8 to 0.9 MPa. The temperature increase rate in the first contraction section may be 0.1 to 10°C / min, more preferably 0.1 to 2°C / min. The temperature increase rate in the second contraction section may be 1 to 10°C / min, more preferably 1 to 5°C / min, thereby making it easier to achieve the object of the present invention.

[0058] Next, the sintering step that is carried out after the second temperature T3 is reached will be described.

[0059] The second temperature T3 may be selected within the range of 1700 to 1900° C. If the temperature is lower than 1700° C., the compact may not be sufficiently densified. If the temperature is higher than 1900° C., overgrowth and / or uneven growth of grains may occur, resulting in a decrease in the mechanical strength of the resulting substrate.

[0060] In this case, the sintering time can be adjusted depending on the range of the second temperature T3 as described above, and when the second temperature T3 is low, the sintering can be performed for a long time, and conversely, when the second temperature T3 is high, the sintering can be performed for a relatively short time compared to the sintering time under low temperature conditions. The sintering can be performed for, for example, 2 to 10 hours, more preferably 4 to 8 hours, which is advantageous for achieving the object of the present invention.

[0061] The sintering process may also be carried out in a nitrogen gas atmosphere. The nitrogen gas pressure may be the same as that used in sintering a silicon nitride molded body, but may be, for example, 0.1 MPa or higher, more preferably 0.9 to 1.0 MPa, and even more preferably 0.9 to 0.98 MPa, which may be advantageous for producing a high-quality silicon nitride substrate.

[0062] The substrate that has been through the sintering section S5 of the heat treatment step may then further undergo a cooling section S6. The cooling section S6 may follow the cooling conditions used after sintering a typical silicon nitride substrate, and the present invention is not particularly limited thereto.

[0063] The silicon nitride substrate manufactured by the above-described manufacturing method may have a thermal conductivity of 75 W / mK or more, preferably 80 W / mK or more, and more preferably 90 W / mK or more, and a three-point bending strength of 650 MPa or more, preferably 680 MPa or more, more preferably 700 MPa or more, and even more preferably 750 MPa or more.

[0064] Furthermore, the substrate preferably contains 6 wt % or less of silicon, more preferably 4 wt % or less, and more preferably 0 wt %, thereby enabling the substrate to have improved mechanical strength and thermal conductivity. [Example]

[0065] The present invention will be described in more detail based on the following examples, but the following examples should not be construed as limiting the scope of the present invention, but should be construed as aiding in the understanding of the present invention.

[0066] Example 1 Polycrystalline silicon scrap (99.99% purity, 1 Ω·cm resistivity) from semiconductor process jigs was dry-ground using a jet mill to prepare metallic silicon powder with an average particle size of 4 μm. 3 mol% yttrium oxide with an average particle size of 0.5 μm and 5 mol% magnesium oxide with an average particle size of 0.5 μm were mixed with this to prepare a ceramic composition. 100 parts by weight of the prepared ceramic composition was mixed with 80 parts by weight of ethanol as a solvent and 10 parts by weight of polyvinyl butyral as an organic binder to produce a slurry for substrate manufacturing. This was then fabricated into sheet-shaped compacts using a tape casting method. Four of the resulting compacts were then stacked and placed in a furnace. They were then heat-treated under a nitrogen gas atmosphere at a pressure of 0.15 MPa at a heating rate of 5°C / min up to 900°C, and then at a heating rate of 1.2°C / min from 900°C to 1000°C. The substrate was then heated from 1000°C to a first temperature of 1460°C at a nitrogen gas pressure of 0.15 MPa at a heating rate of 0.5°C / min, and then heat-treated at the first temperature of 1460°C at a nitrogen gas pressure of 0.17 MPa for 2 hours to obtain a nitrided substrate. The substrate was then heated slowly to 1700°C at a heating rate of 1°C / min under a nitrogen gas pressure of 0.2 MPa, and then heated to a second temperature of 1850°C at a heating rate of 4°C / min under a nitrogen gas pressure of 0.9 MPa. The substrate was sintered at 1850°C for 5 hours under a nitrogen gas pressure of 0.9 MPa to produce a silicon nitride substrate with a final thickness of 170 μm.

[0067] <Examples 2 to 12 and Comparative Examples 1 to 4> The same procedure as in Example 1 was carried out, but the first temperature, second temperature, nitriding section pressure, yttrium oxide content, and magnesium oxide content were changed to prepare silicon nitride substrates as shown in Tables 1 to 3 below.

[0068] <Experimental Example> The silicon nitride substrates produced in Examples 1 to 12 and Comparative Examples 1 to 4 were evaluated for the following physical properties, which are shown in Tables 1 to 3 below.

[0069] 1. Evaluation of three-point bending strength The three-point bending strength of the silicon nitride substrates manufactured in the examples and comparative examples was measured according to the international standard ASTM C 1161-02C (standard test method for Flexural strength of Advanced ceramics at Ambient Temperature) using a universal testing machine, AGS-1000D (Shimadzu, Japan). The test specimen was supported at two support points 20 mm apart, and a load was applied at the midpoint between the two support points using a crosshead moving at a speed of 1 mm per minute. The maximum load at which the test specimen broke was measured, and the bending strength was calculated using the following equation 1.

[0070] [Calculation formula 1] Bending strength (σ) = 3 x P x L / 2 x w x t 2

[0071] In the above formula 1, P represents the maximum load, L represents the length of the test piece, w represents the width of the test piece, and t represents the thickness of the test piece.

[0072] 2.Measurement of thermal conductivity To measure the thermal conductivity of the silicon nitride substrates manufactured in the examples and comparative examples using the international standard ASTM E1461 (standard Test Method for Thermal Diffusivity by the laser Flash Method), test pieces with a thickness of approximately 500 μm and dimensions of 10 mm x 10 mm were prepared, and the thermal diffusivity was measured using a laser flash apparatus (NETZCH, Germany) and calculated using the following equation 2.

[0073] [Formula 2] Thermal conductivity (k) = α·ρ·Cp

[0074] In the above formula 2, α is the thermal diffusion coefficient (mm 2 / S), ρ is the density (g / cm 3 ), and Cp indicates the heat capacity (J / (kg·K)).

[0075] 3. Evaluation of surface condition after sintering This is a phenomenon in which Si does not completely nitride but melts and dissolves in the silicon nitride substrates manufactured in the examples and comparative examples. The surface condition after sintering was evaluated using a method for checking the degree of reaction of the sintered body. (However, for test pieces in which dissolution occurred, it was not possible to manufacture test pieces for measuring thermal conductivity and three-point bending strength, and therefore physical properties could not be measured.)

[0076] [Table 1]

[0077] [Table 2]

[0078] [Table 3]

[0079] As can be seen from Tables 1 to 3, Examples 1 to 3, 5, 7, and 9, which satisfy all of the first temperature, second temperature, nitriding section pressure, yttrium oxide content, and magnesium oxide content according to the present invention, have excellent mechanical strength and thermal conductivity, as well as a good surface condition after sintering, compared to Examples 4, 6, 8, 10 to 12, and Comparative Examples 1 to 4, which do not satisfy any of these.

[0080] The above describes one embodiment and examples of the present invention, but the concept of the present invention is not limited to the embodiments and examples presented in this specification. A person skilled in the art who understands the concept of the present invention can easily propose other embodiments and examples by adding, changing, deleting, or adding components within the scope of the same concept, and these can also be said to fall within the scope of the concept of the present invention. [Explanation of symbols]

[0081] 1, 2 Molded body 10 BN Plate 100 laminate

Claims

1. preparing a ceramic composition including a silicon metal powder and a crystalline phase control powder including a rare earth element-containing compound, which is yttrium oxide, and a magnesium-containing compound, which is magnesium oxide, in a molar ratio of 1:1.5-2.0; mixing the ceramic composition with a solvent and an organic binder to prepare a slurry, and forming a sheet-shaped compact from the slurry; and a heat treatment step including a nitriding section in which heat treatment is performed at a first temperature in the range of 1300 to 1500°C while applying nitrogen gas at a pressure of 0.14 to 0.18 MPa to the compact, and a sintering section in which heat treatment is performed at a second temperature in the range of 1700 to 1900°C. ３ N ４ ) A method for manufacturing a substrate.

2. 2. The method of claim 1, wherein the metal silicon powder is obtained by dry-milling polycrystalline metal silicon scraps or single-crystal silicon wafer scraps to minimize contamination with metal impurities during milling.

3. 2. The method for producing a silicon nitride substrate according to claim 1, wherein the metal silicon powder has a resistivity of 1 to 100 Ω·cm.

4. 3. The method for producing a silicon nitride substrate according to claim 2, wherein the polycrystalline metal silicon scraps or single crystal silicon wafer scraps have a purity of 99% or more.

5. 2. The method for producing a silicon nitride substrate according to claim 1, wherein the metal silicon powder has an average particle size of 0.5 to 4 μm, the rare earth element-containing compound powder has an average particle size of 0.1 to 1 μm, and the magnesium-containing compound powder has an average particle size of 0.1 to 1 μm.

6. 2. The method for producing a silicon nitride substrate according to claim 1, wherein the ceramic composition contains 2 to 5 mol % of the yttrium oxide and 2 to 10 mol % of the magnesium oxide.

7. 2. The method of claim 1, wherein the heat treatment step is performed continuously from the nitriding section to the sintering section.

8. 2. The method of claim 1, wherein the heat treatment is performed from 1000±20° C. to the first temperature at a temperature increase rate of 0.1 to 2° C. / min while supplying nitrogen gas at a pressure of 0.1 to 0.2 MPa.

9. The method for producing a silicon nitride substrate according to claim 1, wherein the nitriding step is carried out for 2 to 10 hours.

10. 9. The method of claim 8, wherein the pressure of the nitrogen gas applied from the temperature of 1000±20° C. to the first temperature is lower than the pressure of the nitrogen gas applied in the nitriding section.

11. 2. The method of claim 1, further comprising: a first contraction section between the nitriding section and the sintering section, in which the temperature is increased from the first temperature to 1700±20°C at a rate of 0.1 to 10.0°C / min under a nitrogen gas pressure of 0.15 to 0.30 MPa; and a second contraction section in which the temperature is increased from 1700±20°C to the second temperature at a rate of 1 to 10°C / min under a nitrogen gas pressure of 0.80 to 0.98 MPa.

12. 2. The method for manufacturing a silicon nitride substrate according to claim 1, wherein the heat treatment step is performed on a plurality of stacked sheet-like bodies.

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