KR20240000013A - Method for Regenerating silicon nitride substrate - Google Patents

Abstract

The present invention relates to a method for recycling silicon nitride substrates, and more specifically, to the steps of classifying substrates that do not meet specifications among manufactured silicon nitride substrates; and performing a re-sintering process on the substrate that does not meet the specifications. The re-sintering process is performed at a temperature of 1600°C to 1900°C, and the re-sintering process can improve the thermal conductivity of the substrate that does not meet the specifications by 10% to 30%.

Description

{Method for Regenerating silicon nitride substrate}

The present invention relates to a method for recycling silicon nitride substrates, and more specifically, to a method for recycling substrates that do not meet specifications.

Ceramic materials with high electrical insulation and thermal conductivity can be used as a heat medium that quickly transfers the heat generated by the device. Ceramic materials are used as substrates for transportation devices, substrates for highly integrated electronic circuits, heat dissipation components for laser oscillators, reaction vessel components for semiconductor manufacturing equipment, and precision mechanical components.

In particular, ceramic substrates used in high-output power devices require high insulation, high withstand voltage, high thermal conductivity, high bending strength, and low dielectric constant. Ceramic substrates suitable for these requirements include aluminum nitride substrates, alumina substrates, and silicon nitride substrates.

Silicon nitride (Si ₃ N ₄ ) substrates have high bending strength (500 MPa to 800 MPa), high toughness (5 MPa·m to 8 MPa·m), and excellent thermal expansion coefficient matching with silicon (Si). Furthermore, the silicon nitride (Si ₃ N ₄ ) substrate has high thermal conductivity (70 W/mK to 170 W/mK). In other words, silicon nitride (Si ₃ N ₄ ) substrates are suitable as a material for next-generation high-output power devices.

The problem to be solved by the present invention is to provide a method for recycling a silicon nitride substrate.

According to the concept of the present invention, a method for recycling silicon nitride substrates includes the steps of classifying substrates that do not meet specifications among manufactured silicon nitride substrates; And it may include performing a re-sintering process on a substrate that does not meet the specifications. The re-sintering process is performed at a temperature of 1600°C to 1900°C, and the re-sintering process can improve the thermal conductivity of the substrate that does not meet the specifications by 10% to 30%.

The method for recycling silicon nitride substrates according to the present invention can regenerate substrates that do not meet specifications and whose thermal conductivity falls below the standard value among manufactured silicon nitride substrates. In other words, the present invention can recycle a substrate that does not meet specifications in a simple way to have thermal conductivity that meets the standard value. This can reduce the amount of waste of manufactured silicon nitride substrates and improve the economic efficiency of the substrate manufacturing process.

1 is a flowchart for explaining a method of manufacturing a silicon nitride substrate according to embodiments of the present invention.
Figure 2 is a schematic diagram for explaining the first step of Figure 1.
3A to 3C are schematic diagrams for explaining the second step in FIG. 1.
Figure 4 is a schematic diagram for explaining the third step of Figure 1.
Figure 5 is a schematic diagram for explaining the fourth step of Figure 1.
FIG. 6 is a schematic diagram for explaining the fifth step of FIG. 1.
Figure 7 is a schematic diagram for explaining the sixth step of Figure 1.
FIG. 8 is a schematic diagram for explaining the seventh step of FIG. 1.
Figure 9 is a flowchart for explaining a method for recycling a silicon nitride substrate manufactured according to embodiments of the present invention.
Figure 10 is a schematic diagram for explaining the first step of Figure 9.
Figure 11 is a schematic diagram for explaining the second step of Figure 9.

In order to fully understand the configuration and effects of the present invention, preferred embodiments of the present invention will be described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various changes can be made. However, the description of the present embodiments is provided to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the present invention of the scope of the invention.

In various embodiments of the present specification, terms such as first, second, and third are used to describe various components, but these components should not be limited by these terms. These terms are merely used to distinguish one component from another. Embodiments described and illustrated herein also include complementary embodiments thereof.

The terminology used herein is for describing embodiments and is not intended to limit the invention. As used herein, singular forms also include plural forms, unless specifically stated otherwise in the context. As used in the specification, 'comprises' and/or 'comprising' does not exclude the presence or addition of one or more other elements.

1 is a flowchart illustrating a method of manufacturing a silicon nitride substrate according to embodiments of the present invention. Referring to FIG. 1, the method for manufacturing a silicon nitride substrate according to embodiments of the present invention includes a first step of preparing a ceramic additive (S110), a second step of mixing silicon nitride powder, a ceramic additive, and a solvent to form a slurry. (S120), a third step of forming a sheet by molding the slurry through a tape casting process (S130), a fourth step of forming a laminated sheet by stacking the sheets and performing a lamination process (S140), between the lower plate and the upper plate A fifth step (S150) of sandwiching the laminated sheet (SSH) to form a laminated structure (SS), a 6th step (S160) of performing a degreasing process on the laminated structure, and a 7th step of performing a sintering process on the laminated structure. It may include step S170.

Figure 2 is a schematic diagram for explaining the first step of Figure 1. Referring to FIGS. 1 and 2 , first balls BA1 and first mixture MI1 may be provided in the first container CON1. The first mixture (MI1) may include ceramic powder and a solvent. Specifically, the first balls BA1 and the solvent may be placed in the first container CON1. Ceramic powder can be added to the solvent. The first balls BA1 may include ceramic such as zirconia. The solvent is an organic solvent and may include, for example, ethanol. The ceramic powder may include yttrium oxide (Y ₂ O ₃ ) and magnesium oxide (MgO).

By mixing the first mixture (MI1) using a mixing device, the ceramic powder can be uniformly mixed in the first mixture (MI1). The first balls BA1 can physically help uniformly mix the ceramic powder. Specifically, yttrium oxide powder and magnesium oxide powder may be uniformly mixed in the first mixture (MI1).

After mixing is completed, the first balls BA1 can be removed. The first mixture (MI1) may be dried to evaporate all of the solvent. As a result, a ceramic additive (SA) in powder form can be obtained (S110). The ceramic additive (SA) may include yttrium oxide (Y ₂ O ₃ ) and magnesium oxide (MgO).

In one embodiment of the present invention, the ceramic powder may be composed only of yttrium oxide (Y ₂ O ₃ ) and magnesium oxide (MgO). In another embodiment of the present invention, the ceramic powder may further include not only yttrium oxide (Y ₂ O ₃ ) and magnesium oxide (MgO), but also additional oxides (for example, zirconium oxide).

The mass ratio of the yttrium oxide (Y ₂ O ₃ ) to the ceramic additive (SA) may be 0.3 to 0.5. The mass ratio of the magnesium oxide (MgO) to the ceramic additive (SA) may be 0.5 to 0.7. The atomic ratio of magnesium (Mg) to yttrium (Y) in the ceramic additive (SA) may be 3 to 5. In other words, the number of magnesium atoms in the ceramic additive (SA) may be 3 to 5 times the number of yttrium atoms.

3A to 3C are schematic diagrams for explaining the second step in FIG. 1.

Referring to FIGS. 1 and 3A , a solvent (SV) and second balls (BA2) may be provided in a second container (CON2). The solvent (SV) is an organic solvent and may include, for example, isopropyl alcohol and toluene. Isopropyl alcohol and toluene can be mixed in a volume ratio of 4:6. The second balls BA2 may include silicon nitride.

A second mixture (MI2) may be prepared by adding silicon nitride (Si ₃ N ₄ ) powder (SNP), a ceramic additive (SA), and a dispersant (DIS) to the solvent (SV) of the second container (CON2). The ceramic additive (SA) may have been previously prepared through the first step (S110). A commercially available dispersant (DIS) can be used, for example, BYK-111.

The solvent (SV) may have 40 Vol% to 60 Vol% with respect to the total volume of the second mixture (MI2). Silicon nitride powder (SNP) may have 15 Vol% to 25 Vol% with respect to the total volume of the second mixture (MI2). The ceramic additive (SA) may have 5 wt% to 10 wt% based on the mass of the second mixture (MI2).

By performing a first ball milling process on the second mixture (MI2), the second mixture (MI2) can be uniformly mixed. The second balls can physically help the second mixture (MI2) be uniformly mixed.

Specifically, the first ball milling process may include rotating the second container containing the second mixture (MI2) at a constant speed using a ball milling machine. As the second container rotates, mechanical grinding and uniform mixing can be performed by the second balls in the second container. The rotation speed of the ball mill may be 100 rpm to 500 rpm.

Referring to FIGS. 1 and 3B , after the first ball milling process, a third mixture (MI3) may be prepared by adding a binder (BI) and a plasticizer (PL) to the second mixture (MI2). The binder (BI) is a cellulose derivative such as ethyl cellulose, methyl cellulose, nitro cellulose, carboxy cellulose, a resin such as polyvinyl alcohol, acrylic acid ester, methacrylic acid ester, polyvinyl butyral, and a mixture of the derivative and the resin. It can contain at least one. For example, the binder (BI) may include polyvinyl butyral (PVB). The plasticizer (PL) may include dibutyl phthalate or dioctyl phthalate. The mass of the added plasticizer (PL) may be about 50% of the mass of the added binder (BI). Additionally, a solvent may be added to the second mixture (MI2).

By performing a second ball milling process on the third mixture (MI3), the third mixture (MI3) can be uniformly mixed. The slurry (SL) may be formed by uniformly mixing the third mixture (MI3) through the second ball milling process (S120). The second ball milling process may be substantially the same as or similar to the first ball milling process described above. The second balls can then be removed.

Referring to FIGS. 1 and 3C , volatile gases may be removed from the slurry (SL) formed through the second ball milling process by aging the slurry (SL). While aging the slurry (SL), the slurry (SL) may be stirred using a stirrer (SIT). Aging may be performed for approximately 24 hours.

Figure 4 is a schematic diagram for explaining the third step of Figure 1.

Referring to FIGS. 1 and 4 , the slurry (SL) prepared in the second step (S120) may be molded through a tape casting process to form a sheet (SH) (S130). Specifically, in the tape casting process, slurry (SL) can be poured onto a blade set at a constant dam height and the slurry (SL) can be applied on a moving substrate film. A sheet (SH) molded body can be obtained by volatilizing the solvent from the slurry (SL) applied on the substrate film and removing it. The substrate film may be a stainless steel tape, oil paper tape, or a polymer tape such as polyester. For example, the slurry (SL) is poured onto a doctor blade set to a dam height of about 0.3 mm, and a substrate film moving at a predetermined speed (e.g., 0.1 m/min to 1 m/min) is applied onto the slurry (SL). may be applied. Afterwards, the sheet (SH) can be obtained by performing a drying process and a process of removing the substrate film.

The tape casting process can be performed at 30°C to 80°C. The sheet (SH) formed through the tape casting process can be cut to an appropriate size. The thickness of the sheet SH may be 0.1 mm to 0.16 mm.

Figure 5 is a schematic diagram for explaining the fourth step of Figure 1.

Referring to FIGS. 1 and 5 , a plurality of sheets SH prepared in the third step (S130) may be stacked. A lamination process may be performed on the stacked sheets (SH) to form a stacked sheet (SSH) (S140). As an example, three to five sheets (SH) may be stacked to form a stacked sheet (SSH). The lamination process can be performed at a pressure of about 10 MPa and a temperature of about 60°C.

Laminated sheets (SSH) can be pressed. The pressurization process may use a warm isostatic press (WIP). The pressurizing process may be performed at a pressure of about 30 MPa and a temperature of about 70°C. Finally, the thickness (TH) of the laminated sheet (SSH) may be 0.3 mm to 4 mm.

FIG. 6 is a schematic diagram for explaining the fifth step of FIG. 1.

Referring to FIGS. 1 and 6 , a laminated structure (SS) may be prepared. The laminated structure SS may include a lower plate (PLT1), an upper plate (PLT2), and a laminated sheet (SSH) interposed between them. Preparing the laminated structure SS may include sandwiching the laminated sheet SSH prepared in the fourth step S140 between the lower plate PLT1 and the upper plate PLT2 (S150). Although FIG. 6 illustrates that one laminated sheet (SSH) is interposed between the lower plate (PLT1) and the upper plate (PLT2), the present invention is not limited thereto. For example, two or more laminated sheets (SSH) may be interposed between the lower plate (PLT1) and the upper plate (PLT2).

Before preparing the laminated structure (SS), boron nitride (BN) can be evenly applied to the laminated sheet (SSH). The lower plate (PLT1) and the upper plate (PLT2) may include boron nitride.

Figure 7 is a schematic diagram for explaining the sixth step of Figure 1.

Referring to FIGS. 1 and 7 , a degreasing process (Binder Burn Out, B.B.O.) may be performed on the laminated structure (SS) prepared in the fifth step (S150) (S160). As a result, all organic substances such as binders, dispersants, and plasticizers in the laminated sheet (SSH) can be incinerated and removed. The degreasing process can be performed in an atmospheric furnace (AF) at a temperature of about 600° C. for about 12 hours. That is, the degreasing process can be performed under atmospheric conditions (air).

FIG. 8 is a schematic diagram for explaining the seventh step of FIG. 1.

Referring to FIGS. 1 and 8 , after the sixth step (S160), a laminated structure (SS) may be provided in the crucible (CRU). By placing bedding powder (BNP) in a crucible (CRU), the laminated structure (SS) may be buried in the bedding powder (BNP). The bedding powder (BNP) may include boron nitride powder, silicon nitride powder, or mixtures thereof. When the bedding powder (BNP) includes a mixture of boron nitride powder and silicon nitride powder, the boron nitride powder and silicon nitride powder may be mixed 1:1.

By heating the crucible (CRU), a sintering process may be performed on the laminated structure (SS) (S170). As a result, the laminated sheet (SSH) can be sintered to form a silicon nitride substrate. The sintering process may be performed at a temperature of 1700°C to 2000°C. For example, the sintering process may be performed at a temperature of about 1900° C. for about 6 hours. The sintering process may be performed in a nitrogen atmosphere. The sintered laminated sheet (SSH) can be obtained as a silicon nitride substrate.

Figure 9 is a flowchart for explaining a method for recycling a silicon nitride substrate manufactured according to embodiments of the present invention. Referring to FIG. 9, the method for recycling silicon nitride substrates according to embodiments of the present invention includes a first step (S210) of classifying substrates that do not meet specifications among manufactured silicon nitride substrates and a re-sintering process for substrates that do not meet specifications. It may include a second step (S220) of performing.

Figure 10 is a schematic diagram for explaining the first step of Figure 9. Referring to Figures 9 and 10, silicon nitride substrates (SNS) can be manufactured according to the manufacturing method of the silicon nitride substrate of the present invention previously described with reference to Figures 1 to 8. Among the manufactured silicon nitride substrates (SNS), those that do not meet specifications (SNS') can be classified (S210).

Silicon nitride substrates (SNS) contain more than 99 wt% SiN, but may contain trace amounts of magnesium (Mg) and yttrium (Y) as impurities. Impurities such as magnesium (Mg) and yttrium (Y) may be residues derived from the ceramic additive (SA) described above.

The concentration (or content) of magnesium (Mg) in the silicon nitride substrate (SNS) may affect the physical properties of the silicon nitride substrate (SNS). For example, the concentration of magnesium (Mg) in a silicon nitride substrate (SNS) can have a close effect on the thermal conductivity and bending strength of the silicon nitride substrate (SNS).

In one embodiment of the present invention, the concentration of magnesium (Mg) in the silicon nitride substrate (SNS) may be inversely proportional to the thermal conductivity of the silicon nitride substrate (SNS). In other words, as the concentration of magnesium (Mg) in the silicon nitride substrate (SNS) increases, the thermal conductivity may decrease. In one embodiment of the present invention, the concentration of magnesium (Mg) in the silicon nitride substrate (SNS) may be proportional to the bending strength of the silicon nitride substrate (SNS). In other words, the higher the concentration of magnesium (Mg) in the silicon nitride substrate (SNS), the higher the bending strength can be.

Among the manufactured silicon nitride substrates (SNS), a substrate (SNS') that does not meet specifications may be a substrate whose thermal conductivity does not meet the first reference value. For example, the first reference value may be 70 W/m·K. However, the first reference value can be changed according to customer needs, and the first reference value of the present invention is not limited to the above example.

Among the manufactured silicon nitride substrates (SNS), a substrate (SNS') that does not meet specifications may be a substrate whose bending strength is greater than the second reference value. For example, the second reference value may be 900 MPa. However, the second reference value can be changed according to customer needs, and the second reference value of the present invention is not limited to the above example.

In one embodiment of the present invention, the concentration of magnesium (Mg) in a substrate (SNS') that does not meet specifications may be greater than 10,000 ppm. For example, the concentration of magnesium (Mg) in a substrate (SNS') that does not meet specifications may be 10,000 ppm to 50,000 ppm. The thermal conductivity of a substrate (SNS') that does not meet specifications may be 50 W/m·K to 70 W/m·K. The bending strength of the substrate (SNS') that does not meet specifications may be 900 MPa to 1000 MPa.

In one embodiment of the present invention, the concentration of magnesium (Mg) in a silicon nitride substrate (SNS) that satisfies specifications may be greater than 10,000 ppm. For example, the concentration of magnesium (Mg) in a silicon nitride substrate (SNS) that satisfies specifications may be 1,000 ppm to 10,000 ppm. The thermal conductivity of a silicon nitride substrate (SNS) that satisfies the specifications may be 70 W/m·K to 170 W/m·K. The bending strength of a silicon nitride substrate (SNS) that meets specifications may be 750 MPa to 900 MPa.

Among the manufactured silicon nitride substrates (SNS), those whose thermal conductivity and/or bending strength do not meet the desired specifications described above may be classified as substrates that do not meet specifications (SNS'). According to the comparative example of the present invention, a substrate (SNS') that does not meet specifications can be disposed of. However, according to an embodiment of the present invention, a substrate (SNS') that does not meet specifications can be regenerated into a substrate that meets specifications.

Figure 11 is a schematic diagram for explaining the second step of Figure 9. Referring to FIGS. 9 and 11 , a re-sintering process may be performed on a classified substrate (SNS') that does not meet specifications (S220). The re-sintering process may be substantially the same or similar to the sintering process of the laminated structure SS described above with reference to FIG. 8.

Specifically, the laminated structure SS' can be prepared again by sandwiching a substrate SNS' that does not meet specifications between the lower plate PLT1 and the upper plate PLT2. A laminated structure (SS') may be provided in a crucible (CRU), and the laminated structure (SS') may be embedded in bedding powder (BNP). By heating the crucible (CRU), a re-sintering process may be performed on the laminated structure (SS') (S220).

The re-sintering process may be performed at a lower temperature than the sintering process of FIG. 8. For example, the re-sintering process can be performed at a temperature of 1600°C to 1900°C. The re-sintering process can be carried out for 6 to 12 hours.

As previously explained, the reason why the thermal conductivity and/or bending strength of the substrate (SNS') that does not meet specifications does not meet the target standard value is that the concentration of magnesium (Mg) in the substrate (SNS') that does not meet specifications is relatively high. Because it's big.

The re-sintering process can remove (or volatilize) magnesium (Mg) in the non-specification substrate (SNS'). The concentration of magnesium (Mg) in a substandard substrate (SNS') that has undergone a re-sintering process may be reduced compared to before. For example, a non-specification substrate (SNS') that has undergone a re-sintering process may have a magnesium (Mg) concentration of 1,000 ppm to 10,000 ppm.

The thermal conductivity of a substandard substrate (SNS') that has gone through a re-sintering process can be improved compared to before. For example, the thermal conductivity of a substandard substrate (SNS') that has gone through a re-sintering process can be improved by 10% to 30% compared to before. The thermal conductivity of a non-specification substrate (SNS') that has undergone a re-sintering process may be 70 W/m·K to 170 W/m·K.

The flexural strength of an out-of-spec substrate (SNS') that has undergone a re-sintering process may be reduced compared to before. For example, the bending strength of a substandard substrate (SNS') that has undergone a re-sintering process may be reduced by 10% to 30% compared to before. The bending strength of the sub-spec substrate (SNS') that has gone through the re-sintering process may be 750 MPa to 900 MPa.

The method of recycling a silicon nitride substrate according to the present invention does not discard a substrate that does not meet specifications, but can regenerate (or recycle) a substrate that satisfies the desired specifications through a re-sintering process. The silicon nitride substrate thus manufactured can be recycled and reused in a simple way rather than being discarded, thereby improving the economic efficiency of the substrate manufacturing process.

Experiment example

A silicon nitride substrate was manufactured through the manufacturing method described in FIGS. 1 to 8 of the present invention. The thermal conductivity and bending strength of the manufactured silicon nitride substrate were measured. The thermal conductivity and bending strength of the prepared silicon nitride substrate were 67.121 W/m·K and 956.61 MPa, respectively.

The re-sintering process of the present invention was performed on a silicon nitride substrate. A first substrate (Experimental Example 1) on which the re-sintering process was performed at 1600°C for 6 hours and a second substrate (Experimental Example 2) on which the resintering process was performed at 1600°C for 12 hours were obtained. The thermal conductivity and bending strength were measured for the first and second substrates, respectively, and are shown in Table 1 below.

Bending strength (MPa) Thermal conductivity (W/m·K) Manufactured silicon nitride substrate 956.61 67.121 Experimental Example 1 838.04 (-12.4%) 83.65 (+24.6%) Experimental Example 2 674 (-29.5%) 81.36 (+21.2%)

Referring to Table 1, as a result of performing the re-sintering process on the silicon nitride substrate, it was confirmed that the thermal conductivity increased by more than about 20% and the bending strength decreased by about 10% to about 30%. As a result, it can be confirmed that even a silicon nitride substrate whose thermal conductivity does not meet the standard value can be regenerated (or recycled) by increasing the thermal conductivity through the re-sintering process. When the re-sintering process time is increased from 6 hours to 12 hours, the bending occurs. It was confirmed that the strength decreased more significantly, but there was no significant difference in the change in thermal conductivity.

The re-sintering process of the present invention was performed on the previously prepared silicon nitride substrate. A first substrate on which the re-sintering process was performed at 1600°C for 6 hours (Experimental Example 1), a third substrate on which the re-sintering process was performed at 1700°C for 6 hours (Experimental Example 3), and a fourth substrate on which the resintering process was performed at 1800°C for 6 hours. (Experimental Example 4) was obtained. The thermal conductivity and bending strength were measured for the first, third, and fourth substrates, respectively, and are shown in Table 2 below.

Bending strength (MPa) Thermal conductivity (W/m·K) Manufactured silicon nitride substrate 956.61 67.121 Experimental Example 1 838.04 (-12.4%) 83.65 (+24.6%) Experimental Example 3 830.42 (-13.2%) 75.24 (+12.1%) Experimental Example 4 815.98 (-14.7%) 83.25 (+24.0%)

Referring to Table 2, it can be seen that when the re-sintering process was performed on the silicon nitride substrate at a temperature of 1600°C to 1800°C, the thermal conductivity greatly increased and the bending strength decreased.

Above, embodiments of the present invention have been described with reference to the attached drawings, but those skilled in the art will understand that the present invention can be implemented in other specific forms without changing the technical idea or essential features. You will understand that it exists. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims (10)

Classifying substrates that do not meet specifications among the manufactured silicon nitride substrates; and
Including performing a re-sintering process on a substrate that does not meet the specifications,
The re-sintering process is carried out at a temperature of 1600°C to 1900°C,
The re-sintering process is a method of recycling a silicon nitride substrate that improves the thermal conductivity of a substrate that does not meet the specifications by 10% to 30%.
According to paragraph 1,
A method of recycling a silicon nitride substrate, wherein the re-sintering process reduces the bending strength of the substrate that does not meet the specifications.
According to paragraph 2,
A method of recycling a silicon nitride substrate, wherein the re-sintering process reduces the bending strength of the substrate that does not meet the specifications by 10% to 30%.
According to paragraph 1,
A method for recycling a silicon nitride substrate, wherein the re-sintering process is performed for 6 to 12 hours.
According to paragraph 1,
A method of recycling a silicon nitride substrate, wherein the re-sintering process reduces the concentration of magnesium (Mg) in the substrate that does not meet the specifications.
According to paragraph 1,
Manufacturing the silicon nitride substrates is a method of recycling a silicon nitride substrate comprising the following steps:
Mixing silicon nitride powder, ceramic additives, and solvent to form a slurry;
forming a sheet by molding the slurry;
sandwiching at least one of the sheets between a lower plate and an upper plate to form a laminate structure;
performing a degreasing process on the laminated structure; and
Performing a sintering process on the layered structure.
According to clause 6,
A method for recycling a silicon nitride substrate, wherein the sintering process is performed at a higher temperature than the re-sintering process.
According to clause 6,
The ceramic additive includes yttrium oxide (Y ₂ O ₃ ) and magnesium oxide (MgO),
A method of manufacturing a silicon nitride substrate wherein the atomic ratio of magnesium (Mg) to yttrium (Y) in the ceramic additive is 3 to 5.
According to paragraph 1,
A method of recycling a silicon nitride substrate that does not meet the above specifications and has a thermal conductivity of 50 W/m·K to 70 W/m·K.
According to paragraph 1,
A method of recycling a silicon nitride substrate where the substrate that does not meet the specifications has a bending strength of 900 MPa to 1000 MPa.

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