Green sheet, method of manufacturing silicon nitride substrate with reduced warpage and silicon nitride substrate manufactured thereby

Abstract

A green sheet is provided comprising a silicon nitride sheet layer and a boron nitride sheet layer laminated on one or both sides of the silicon nitride sheet layer.

Description

Technology Field

[0001] The present invention relates to a green sheet, a method for manufacturing a silicon nitride substrate with suppressed warping, and a silicon nitride substrate manufactured therefrom. Background Technology

[0003] Recently, the use of high-power electronic circuit boards, such as power modules for electric vehicles and inverters for wind and solar power generation, has been increasing, and insulating ceramic substrates are being used to implement these circuit boards. Among insulating ceramic substrates, silicon nitride sintered substrates, in particular, are seeing a rapid increase in usage as insulating substrates for electric vehicle power modules due to their excellent mechanical strength. The problem to be solved

[0005] The objective of the present invention is to provide a green sheet capable of manufacturing a ceramic sintered substrate having excellent flatness.

[0006] The objective of the present invention is to provide a method for manufacturing a silicon nitride substrate capable of achieving excellent flatness by suppressing warping.

[0007] The objective of the present invention is to provide a silicon nitride substrate that can improve bonding strength with a metal thin film by suppressing bending and achieving excellent flatness.

[0008] The objects of the present invention are not limited to those mentioned above, and other unmentioned objects and advantages of the present invention may be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims. means of solving the problem

[0010] In one embodiment of the present invention, a green sheet is provided comprising a silicon nitride sheet layer and a boron nitride sheet layer laminated on one or both sides of the silicon nitride sheet layer.

[0011] The silicon nitride sheet layer and the boron nitride sheet layer may be compressed.

[0012] The silicon nitride sheet layer comprises at least one silicon nitride sheet, and in the case of comprising a plurality of silicon nitride sheets, the plurality of silicon nitride sheets may be compressed.

[0013] The boron nitride sheet layer described above may include a biaxially oriented boron nitride sheet.

[0014] The boron nitride sheet layer may include a boron nitride sheet with a thickness of 10 μm to 20 μm.

[0016] In one embodiment of the present invention,

[0017] A step of interposing at least one green sheet between an upper plate and a lower plate;

[0018] A step of performing a degreasing process on the above green sheet;

[0019] A step of performing a sintering process on the above green sheet; and

[0020] A step of obtaining a silicon nitride substrate from the above green sheet;

[0021] A method for manufacturing a silicon nitride substrate with suppressed warping is provided.

[0022] In the above method, the green sheet can be formed by compressing a silicon nitride sheet layer and a boron nitride sheet layer.

[0023] In the above method, the silicon nitride sheet layer among the green sheets can be constrained and sintered by the boron nitride sheet layer.

[0024] In the above method, one or more green sheets may be interposed.

[0025] In the above method, the silicon nitride sheet layer comprises at least one silicon nitride sheet, and in the case where it comprises a plurality of silicon nitride sheets, the plurality of silicon nitride sheets may be compressed.

[0026] In the above method, the boron nitride sheet layer may be formed by compressing a plurality of boron nitride sheets with a thickness of 10 μm to 20 μm.

[0027] In the above method, the silicon nitride sheet can be formed into a sheet by tape casting from silicon nitride powder.

[0028] The above sintering process is

[0029] Stage of raising the temperature;

[0030] A step of maintaining a predetermined temperature; and

[0031] It may include a cooling step.

[0032] The above cooling step can be performed by leaving the green sheet undisturbed without separately performing a process to control the cooling temperature or cooling rate.

[0034] In one embodiment of the present invention, a silicon nitride substrate is manufactured according to a method for manufacturing a silicon nitride substrate with suppressed bending, and the diagonal length (L, mm) of the silicon nitride substrate manufactured in a rectangular shape is scanned by a non-contact 3D measuring instrument, and the difference (ΔZ, mm) between the lowest point and the highest point of one surface of the silicon nitride substrate is measured in the height direction from a sample holder, and the value of the ratio of the measured diagonal length (L) to ΔZ, ΔZ / L (mm / mm), is calculated to be 0.002 or less.

[0035] The silicon nitride substrate comprises a sintered silicon nitride sheet layer and a sintered boron nitride sheet layer, and the sintered boron nitride sheet layer may have a thickness of 10 μm to 20 μm.

[0036] The silicon nitride substrate may be formed by constrained sintering of a compressed silicon nitride sheet layer and a boron nitride sheet layer.

[0037] The silicon nitride substrate comprises a sintered boron nitride sheet layer, and the sintered boron nitride sheet layer may have a thickness of 10 μm to 20 μm. Effects of the invention

[0039] According to the present invention, a silicon nitride substrate can be manufactured that suppresses bending and has excellent flatness when bonding a metal thin film.

[0040] In addition to the effects described above, the specific effects of the present invention are described together with the specific details for implementing the invention below. Brief explanation of the drawing

[0042] FIG. 1 is a cross-sectional view of the green sheet according to one embodiment. FIG. 2 is a cross-sectional view of the green sheet according to another embodiment. FIG. 3 is a schematic diagram schematically showing a silicon nitride sheet layer in a green sheet according to one embodiment. FIG. 4 is a schematic diagram showing a green sheet according to one embodiment formed by laminating a boron nitride sheet layer and a silicon nitride sheet layer. FIG. 5 is a flowchart of a method for manufacturing a silicon nitride substrate with suppressed warping. Specific details for implementing the invention

[0043] The aforementioned objectives, features, and advantages are described in detail below with reference to the attached drawings, thereby enabling those skilled in the art to easily implement the technical concept of the present invention. In describing the present invention, detailed descriptions of known technologies related to the present invention are omitted if it is determined that such descriptions would unnecessarily obscure the essence of the invention. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the attached drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0044] In the following, the statement that any configuration is placed on the "upper (or lower)" of a component or on the "upper (or lower)" of a component may mean not only that any configuration is placed in contact with the upper (or lower) surface of said component, but also that another configuration may be interposed between said component and any configuration placed on (or below) said component.

[0045] In addition, where it is stated that one component is "connected," "combined," or "connected" to another component, it should be understood that while the components may be directly connected or connected to each other, another component may be "interposed" between each component, or each component may be "connected," "combined," or "connected" through another component.

[0046] In one embodiment of the present invention, a green sheet is provided comprising a silicon nitride sheet layer and a boron nitride sheet layer laminated on one or both sides of the silicon nitride sheet layer.

[0047] In this specification, the ‘green sheet’ is a laminated sheet formed from a sheet formed from a ceramic material by a lamination process, which is subject to a sintering process, and can form a ceramic sintered substrate (referred to as a silicon nitride substrate in this specification) by the sintering process.

[0048] FIG. 1 is a cross-sectional view of the green sheet (100) according to one embodiment.

[0049] FIG. 1 shows a green sheet in which the boron nitride sheet layer (10) is formed on one side of the silicon nitride sheet layer (20).

[0050] FIG. 2 is a cross-sectional view of the green sheet (200) according to another embodiment.

[0051] FIG. 2 shows a green sheet (200) in which the boron nitride sheet layer (10) is formed on both sides of the silicon nitride sheet layer (20).

[0052] The silicon nitride sheet layer (20) comprises at least one silicon nitride sheet (1), and in the case where it comprises a plurality of silicon nitride sheets (1), the plurality of silicon nitride sheets (1) can be formed by compressing them.

[0053] The above green sheet (100, 200) can have its bending suppressed as the silicon nitride sheet layer (20) is constrained by the boron nitride sheet layer (10) during the sintering process, and accordingly, a silicon nitride substrate with suppressed bending can be manufactured from the above green sheet (100, 200).

[0054] Although conventional boron nitride powder is applied to the green sheet as a release agent, the green sheet (100, 200) forms the boron nitride sheet layer (10) instead of applying the boron nitride powder.

[0055] The above green sheet (100, 200) can be used to manufacture a ceramic sintered substrate with excellent flatness. To function as a circuit board, a copper thin film is bonded to a ceramic substrate, such as a silicon nitride substrate, and a semiconductor device is die-attached to the copper thin film for operation. Since the semiconductor device operates under high voltage, the heat generated at this time is very high, and the heat generated per unit area reaches 30 times that of an electric iron. Due to this rapid generation of heat, heat is transferred to the copper thin film and the ceramic substrate. At this time, due to the different coefficients of thermal expansion of the copper thin film and the ceramic substrate, the heterogeneous bonding surface between the copper thin film and the ceramic substrate may delaminate, ultimately leading to a problem where the reliability of the circuit board is reduced. Therefore, the bonding strength between the copper thin film and the ceramic substrate is a major physical property that guarantees the product reliability of the circuit board. The flatness of the ceramic substrate can have a significant impact on the bonding strength with the copper thin film. If the flatness of the ceramic substrate falls below a certain standard, the bonding strength between the copper thin film and the ceramic substrate decreases, ultimately leading to a decline in the product reliability of the circuit board.

[0056] The ceramic substrate (silicon nitride substrate described later) manufactured by sintering the above green sheet (100, 200) has excellent flatness, and therefore, the circuit board manufactured by bonding a copper thin film to the ceramic substrate has excellent flatness.

[0057] The thickness of the ceramic substrate obtained by sintering the existing green sheet is thin, and since shrinkage occurs as the green sheet formed from a ceramic material such as silicon nitride powder is sintered and transformed into a ceramic substrate, bending deformation occurs in the thin ceramic substrate after sintering. Since such bending deformation (or reduction in flatness) causes a decrease in bonding strength when bonding a copper thin film, the bending deformation must be controlled to below a certain standard. The bending deformation of the above green sheet (100, 200) can be controlled to below a certain standard during sintering.

[0058] The silicon nitride sheet layer (20) comprises at least one silicon nitride sheet (1), and if it comprises a plurality of silicon nitride sheets, the plurality of silicon nitride sheets may be compressed.

[0059] The silicon nitride sheet (1) above can be formed by sheet molding from silicon nitride powder by tape casting. Specifically, the process of molding the silicon nitride sheet (1) above is described exemplarily below.

[0060] A slurry can be prepared by mixing silicon nitride powder, a ceramic additive, a solvent, optionally a dispersant, optionally a binder, and optionally a plasticizer, and then molding the slurry to form a silicon nitride sheet (1). The solvent may be an organic solvent, and at least one selected from, for example, ethanol, isopropyl alcohol, toluene, etc. The ceramic additive may include at least one selected from yttrium oxide (Y2O3), magnesium oxide (MgO), zirconium oxide, etc. The silicon nitride sheet (1) formed by sheet molding may be obtained by, for example, performing tape casting on the slurry. The dispersant may be a commercially available dispersant, and for example, BYK-111, a type of ester-based block copolymer manufactured by BYK Chemie of Germany, may be used. The binder may include, for example, polyvinyl butyral (PVB). The above plasticizer may include, for example, dibutyl phthalate or dioctyl phthalate.

[0061] Volatile gases can be removed from the slurry by aging the slurry containing silicon nitride powder. During the aging of the slurry, the slurry can be stirred using a stirrer. Aging can be performed for about 24 hours.

[0062] The silicon nitride sheet (1) can be formed by molding the slurry prepared as described above using a tape casting process. Specifically, the tape casting process may involve pouring the slurry onto a blade set to a certain dam height and applying the slurry onto a moving substrate film. The solvent applied to the substrate film may be evaporated and removed to obtain a molded body of the silicon nitride sheet (1). The substrate film may be a stainless steel tape, oil paper tape, or a polymer tape such as polyester. For example, the slurry may be poured onto a doctor blade set to a dam height of about 0.3 mm, and the slurry may be applied onto a substrate film moving at a predetermined speed (e.g., 0.1 m / min to 1 m / min). Subsequently, a drying process and a process of removing the substrate film may be performed to obtain the silicon nitride sheet (1).

[0063] The tape casting process can be performed at 30°C to 80°C. The silicon nitride sheet (1) formed by the tape casting process can be cut to an appropriate size. For example, the thickness of the silicon nitride sheet (1) can be 0.1 mm to 0.16 mm.

[0064] The silicon nitride sheet (1) may have a size of M × N. For example, M and N may each be 60 mm to 300 mm, but are not particularly limited. That is, M and N may each be changed depending on the size of the silicon nitride substrate to be finally manufactured.

[0065] Although the method for manufacturing the silicon nitride sheet (1) described above has been described by way of example, it is not limited thereto and can be manufactured according to known methods to achieve desired physical properties or for use.

[0067] FIG. 3 is a schematic diagram showing the silicon nitride sheet layer (20) formed by stacking a plurality of silicon nitride sheets (1) by compression.

[0068] A plurality of silicon nitride sheets (1) manufactured as described above can be laminated. A lamination process can be performed on the laminate of the plurality of silicon nitride sheets (1) to form the silicon nitride sheet layer (20). For example, three to five silicon nitride sheets (1) can be laminated to form the silicon nitride sheet layer (20). The lamination process can be performed at a pressure of about 10 MPa and a temperature of about 60°C.

[0069] The silicon nitride sheet layer (20) can be formed by applying pressure. The pressure application process performed on the silicon nitride sheet layer (20) may utilize a warm isostatic press (WIP). The pressure application process may be performed at a pressure of about 30 MPa and a temperature of about 70°C. Finally, the thickness (TH) of the formed silicon nitride sheet layer (20) may be 0.3 mm to 4 mm.

[0070] The silicon nitride sheet layer (20) is formed by overlapping the silicon nitride sheet (1), and the size of the silicon nitride sheet layer (20) may also be substantially the same as the size of the silicon nitride sheet (1). In other words, the silicon nitride sheet layer (20) may have a size of M × N. Each of M and N may be 60 mm to 300 mm.

[0072] Separately from the silicon nitride sheet layer (20), the boron nitride sheet layer (10) is manufactured. The boron nitride sheet layer (10) can be formed into a sheet by tape casting from boron nitride powder.

[0073] The green sheet (100, 200) is formed as a single sheet by compressing the boron nitride sheet layer (10) and the silicon nitride sheet layer (20). As the green sheet (100, 200) is formed as a single sheet, the bonding force between the boron nitride sheet layer (10) and the silicon nitride sheet layer (20) is strengthened. This can be contrasted with the state in which the applied boron nitride particles are simply placed on the silicon nitride sheet layer (20) when boron nitride particles are applied as a release agent to the green sheet or when the mixture is made into a slurry and spray-applied.

[0074] The above green sheet (100, 200) can be manufactured into a substrate by performing a sintering process. In the process of sintering the above green sheet (100, 200), the silicon nitride sheet layer (20) undergoes shrinkage due to inter-particle densification, but the boron nitride sheet layer (10) undergoes less or no shrinkage. Because the bonding force between the boron nitride sheet layer (10) and the silicon nitride sheet layer (20) is strong, the boron nitride sheet layer (10) acts as a support for the shrinkage of the silicon nitride sheet layer (20). As a result, the boron nitride sheet layer (10) compressed against the boron nitride sheet layer (10) acts as a restraining force during the shrinkage of the silicon nitride sheet layer (20), thereby applying an even shrinkage force to the entire silicon nitride substrate being manufactured, and can suppress warping of the sintered body after sintering.

[0076] In the silicon nitride substrate obtained by sintering the above green sheets (100, 200), the silicon nitride sheet layer (20) undergoes more shrinkage due to densification than the boron nitride sheet layer (10), so one side of the silicon nitride sheet layer (20) may have a smaller size than the boron nitride sheet layer (10).

[0077] In one embodiment, the boron nitride sheet layer (10) may include a boron nitride sheet with a thickness of 10 μm to 20 μm. The green sheet (100, 200) may include the boron nitride sheet layer (10) with a thickness within the above numerical range, thereby allowing the silicon nitride sheet layer (20) to form a sintered body with the silicon nitride sheet layer (20) having a densified structure while providing a suitable restraining force to the silicon nitride sheet layer (20) during sintering.

[0078] In one embodiment, the silicon nitride sheet layer (20) can be formed using a sheet-molded boron nitride sheet to manufacture the green sheet (100, 200).

[0079] The boron nitride sheet above can be formed in a manner similar to the method of forming a sheet from silicon nitride powder by tape casting in the silicon nitride sheet (1). For example, a slurry containing boron nitride powder instead of silicon nitride can be prepared, the slurry can be applied onto a substrate film, and then the solvent can be evaporated from the slurry to obtain a molded body of the boron nitride sheet. Specifically, the process of forming the boron nitride sheet above will be described exemplarily below.

[0080] A slurry can be prepared by mixing boron nitride powder, a binder, a solvent, optionally a dispersant, optionally a plasticizer, etc., and then molding the slurry to form a boron nitride sheet. In one embodiment, the slurry may comprise 100 parts by weight of boron nitride powder, 0.5 to 3 parts by weight of a dispersant, 5 to 20 parts by weight of an organic binder, 2 to 8 parts by weight of a plasticizer, and 100 to 200 parts by weight of an organic solvent. With respect to the slurry, for example, tape casting can be performed to obtain a sheet-molded boron nitride sheet.

[0081] The boron nitride sheet layer (10) can be biaxially oriented. As previously described, to form the boron nitride sheet layer (10), a boron nitride sheet is first formed and then compressed with a silicon nitride sheet layer (20) to form the boron nitride sheet layer (10). In this way, the boron nitride sheet layer (10) can be formed from a pre-manufactured boron nitride sheet and can be biaxially oriented. Since the boron nitride particles used in manufacturing the boron nitride sheet may be, for example, non-spherical particles with an aspect ratio, specifically in the shape of flakes, they can be biaxially oriented when forming the sheet through a process such as tape casting. This can be contrasted with the case where the applied boron nitride particles are formed non-oriented when boron nitride particles are applied as a release agent to a green sheet or spray-applied as a slurry. In the biaxially oriented boron nitride sheet layer (10), for example, elongated flake-shaped powders are arranged so as to be connected to one another, that is, oriented, so that the bonding strength between the powders is good and uniform heat can be transferred to the silicon nitride sheet layer (20). In this way, as the heat transfer becomes more uniform, all other physical properties of the resulting green sheet (100, 200), including bending, can be improved.

[0083] FIG. 4 is a schematic diagram showing a green sheet (100) formed by laminating the boron nitride sheet layer (10) and the silicon nitride sheet layer (20).

[0084] The boron nitride sheet layer (10) obtained as described above can be laminated onto at least one surface of the silicon nitride sheet layer (20), and then compressed and attached to form the green sheet (100, 200). The process of laminating the boron nitride sheet layer (10) onto the silicon nitride sheet layer (20) and compressing it can, for example, utilize an isostatic hydraulic press.

[0086] In one embodiment of the present invention,

[0087] A step of interposing at least one green sheet between an upper plate and a lower plate;

[0088] A step of performing a degreasing process on the above green sheet;

[0089] A step of performing a sintering process on the above green sheet; and

[0090] A step of obtaining a silicon nitride substrate from the above green sheet;

[0091] A method for manufacturing a silicon nitride substrate with suppressed warping is provided.

[0092] FIG. 5 is a flowchart of a method for manufacturing a silicon nitride substrate with suppressed warping. Referring to FIG. 5, the method for manufacturing a silicon nitride substrate with suppressed warping may include the step of interposing at least one green sheet (100, 200) between an upper plate and a lower plate (S10), the step of performing a degreasing process on the green sheet (100, 200) (S20), the step of performing a sintering process on the green sheet (100, 200) (S30), and the step of obtaining a silicon nitride substrate from the green sheet (100, 200) (S40).

[0093] Although only one green sheet (100, 200) may be interposed between the upper plate and the lower plate, a laminated structure can be formed by stacking multiple green sheets (100, 200) to simultaneously perform sintering on multiple green sheets (100, 200). The laminated structure can be formed by stacking multiple green sheets (100, 200) as they are without performing an additional compression process. By forming a laminated structure in this manner and simultaneously performing a sintering process on multiple green sheets (100, 200), multiple silicon nitride substrates can be manufactured in a single process. Among the green sheets (100, 200), the boron nitride sheet layer (10) prevents aggregation between multiple silicon nitride substrates after sintering.

[0094] The silicon nitride substrate manufactured above can be manufactured in a state where the boron nitride sheet layer (10) is pressed onto the silicon nitride sheet layer (20).

[0095] In this specification, the 'silicon nitride substrate' is a substrate comprising a sintered silicon nitride sheet layer, and may also comprise a sintered boron nitride sheet layer.

[0096] The upper plate and the lower plate may include boron nitride. For example, the upper plate and the lower plate may be boron nitride plates.

[0097] As described above, one or more green sheets (100, 200) may be interposed between the upper plate and the lower plate, and in one embodiment, more than one green sheet (100, 200) may be stacked and interposed between the upper plate and the lower plate. For example, 5 to 20 green sheets (100, 200) may be interposed between the upper plate and the lower plate.

[0099] A degreasing process (Binder Burn Out, BBO) may be performed on the green sheet (100, 200) prepared as above or on a laminated structure containing the same. By doing so, all organic materials such as binders, dispersants, and plasticizers within the green sheet (100, 200) can be incinerated and removed. In one embodiment, the degreasing process may be performed at a predetermined temperature under atmospheric pressure for about 30 to 100 hours. For example, the degreasing process may be performed under atmosphere (air). For example, the degreasing process may be performed in an atmospheric furnace (AF) at a temperature of about 600°C for about 30 hours.

[0101] A sintering process may be performed on the degreased green sheet (100, 200) or the laminated structure containing it. Following the degreased process, the green sheet (100, 200) or the laminated structure containing it may be provided in a crucible. Bedding powder may be placed in the crucible so that the green sheet (100, 200) or the laminated structure containing it may be embedded in the bedding powder. The bedding powder may include boron nitride powder, silicon nitride powder, or a mixture thereof. If the bedding powder includes a mixture of boron nitride powder and silicon nitride powder, the boron nitride powder and silicon nitride powder may be mixed in a 1:1 ratio.

[0102] A crucible can be heated to perform a sintering process on a green sheet (100, 200) or a laminated structure including the same. By doing so, the green sheet (100, 200) is constrained sintered, and a silicon nitride substrate can be formed.

[0104] The above sintering process is

[0105] Stage of raising the temperature;

[0106] A step of maintaining a predetermined temperature; and

[0107] It may include a cooling step.

[0108] In one embodiment, the sintering process may be maintained for 6 to 12 hours after being heated to a temperature of 1700°C to 2000°C. For example, in the sintering process, it may be performed by being heated to a temperature of about 1900°C and maintained for about 6 hours. Subsequently, the cooling step may be performed by leaving the laminated structure undisturbed without separately performing a process to control the cooling temperature or the cooling rate. For example, the cooling step may be performed by rapidly cooling the green sheet (100, 200) or the laminated structure containing it by leaving it in a sintering furnace.

[0109] The method for manufacturing the above-mentioned silicon nitride substrate with suppressed warping involves sintering a green sheet (100, 200) attached to a silicon nitride sheet layer (20) by a boron nitride sheet layer (10), thereby causing the silicon nitride sheet layer (20) to be constrained and sintered by the boron nitride sheet layer (10), so that the silicon nitride substrate is manufactured and the warping is suppressed. Therefore, it may not be necessary to additionally control the cooling temperature or cooling rate during cooling in the sintering process to suppress warping.

[0110] In order to sinter a silicon nitride sheet layer (20), conditions are required to raise the sintering temperature and maintain it for a certain period of time. By keeping the sintering temperature within the above range, the silicon nitride particles are properly densified through growth and rearrangement, and the sintering aid does not volatilize too much, making it suitable for manufacturing a dense sintered body. However, since the process of raising a large sintering furnace to a maximum of 2000°C, maintaining it for a certain period of time, and then cooling it to recover the sintered body is a process that requires a long time, the long operating time in the sintering process leads to a decrease in productivity. The operating time of the sintering process is determined by factors such as the heating rate, maximum temperature, holding time, and cooling time, but there are limits to controlling the heating rate, maximum temperature, and holding time to realize the physical properties of the product. Therefore, it may be advantageous to reduce the cooling time in order to reduce the time of the sintering process. Previously, it was necessary to control the cooling speed because the warping of the substrate increased when cooling was performed rapidly for more than a certain period of time. However, the method for manufacturing the silicon nitride substrate with suppressed warping does not require intentionally slowing down the cooling speed; instead, even if cooling is performed at the maximum possible speed, a sintered body with controlled warping of the substrate can be obtained, thereby reducing the time of the sintering process and increasing productivity.

[0111] The above sintering process can be performed in a nitrogen atmosphere. After sintering a green sheet (100, 200) or a laminated structure containing the same, a silicon nitride substrate derived from individual green sheets (100, 200) can be obtained.

[0113] The layer of the silicon nitride substrate attributable to the silicon nitride sheet layer (20) may have a size of M × N and may have a smaller size than the layer attributable to the boron nitride sheet layer (10), for example, M and N may each be 40 mm to 200 mm. The size of the layer attributable to the silicon nitride sheet layer (20) attributable to the silicon nitride substrate may shrink during the sintering process and become smaller than the size of the green sheet (100, 200).

[0114] The silicon nitride substrate manufactured by the above method for manufacturing a silicon nitride substrate with suppressed warping can exhibit excellent flatness as it is manufactured with suppressed warping.

[0115] In one embodiment, the silicon nitride substrate manufactured according to the method for manufacturing the silicon nitride substrate with suppressed warping can achieve a flatness of 0.002 or less by scanning the diagonal length (L, mm) of the silicon nitride substrate manufactured in a square shape with a non-contact 3D measuring instrument and measuring the difference (ΔZ, mm) between the lowest point and the highest point of one surface of the silicon nitride substrate in the height direction from the sample holder, and calculating the ratio of the measured diagonal length (L) to ΔZ, ΔZ / L (mm / mm).

[0116] The silicon nitride substrate can be applied as an insulating ceramic substrate used in circuit boards. In one embodiment, the silicon nitride substrate can be applied as an insulating substrate for a power module for an electric vehicle.

[0118] In one embodiment of the present invention, a silicon nitride substrate is provided in which the diagonal length (L, mm) of the silicon nitride substrate manufactured according to the method for manufacturing a silicon nitride substrate with suppressed warping is scanned by a non-contact 3D measuring instrument, and the difference (ΔZ, mm) between the lowest point and the highest point of one surface of the silicon nitride substrate is measured in the height direction from a sample holder, and the calculated value of the ratio of the measured diagonal length (L) to ΔZ, ΔZ / L (mm / mm), is 0.002 or less. Since the boron nitride sheet layer included in the green sheet is sintered, the silicon nitride substrate comprises a sintered boron nitride sheet layer, and the sintered boron nitride sheet layer may have a thickness of 10 μm to 20 μm. The sintered boron nitride sheet layer may comprise a boron nitride sheet with a thickness of 10 μm to 20 μm.

[0120] In one embodiment of the present invention, a silicon nitride substrate is provided, formed by constraining a compressed silicon nitride sheet layer (20) and a boron nitride sheet layer. The silicon nitride substrate may be manufactured according to the method for manufacturing a silicon nitride substrate with suppressed warping described above. Since the boron nitride sheet layer included in the green sheet is sintered, the silicon nitride substrate comprises a sintered boron nitride sheet layer, and the sintered boron nitride sheet layer may have a thickness of 10 μm to 20 μm. The sintered boron nitride sheet layer may comprise a boron nitride sheet with a thickness of 10 μm to 20 μm.

[0122] Examples and comparative examples of the present invention are described below. The following examples are merely embodiments of the present invention, and the present invention is not limited to the following examples.

[0124] (Example)

[0125] Example 1

[0126] A boron nitride sheet with a thickness of 15 μm was laminated onto one side of a silicon nitride sheet, and the boron nitride sheet and silicon nitride sheet were compressed using an isostatic hydraulic press at 70°C and 30 MPa for 15 minutes. Ten compressed green sheets were laminated, placed in a boron nitride crucible, and maintained at 1930°C for 6 hours. After cooling, the furnace was opened at 150°C to obtain a sintered substrate. The total time required for the sintering process was 24 hours. From this, ten silicon nitride substrates were manufactured.

[0128] Example 2

[0129] A boron nitride sheet with a thickness of 15 μm was laminated onto one side of a silicon nitride sheet, and the boron nitride sheet and silicon nitride sheet were compressed using an isostatic hydraulic press at 70°C and 30 MPa for 15 minutes. Ten compressed green sheets were laminated, loaded into a boron nitride crucible, and maintained at 1930°C for 6 hours. After cooling the first cooling zone at a rate of 10°C / min and maintaining at 1600°C for 1 hour, the second cooling zone was cooled at a rate of 3.7°C / min. Below 800°C, the furnace was cooled, and the furnace was opened at 150°C to obtain a sintered substrate. The total time required for the sintering process was 26 hours. From this, ten silicon nitride substrates were manufactured.

[0131] Example 3

[0132] A boron nitride sheet with a thickness of 15 μm was laminated onto one side of a silicon nitride sheet, and the boron nitride sheet and silicon nitride sheet were compressed using an isostatic hydraulic press at 70°C and 30 MPa for 15 minutes. After laminating 10 compressed green sheets, they were placed in a boron nitride crucible and maintained at 1930°C for 6 hours. After cooling, a large amount of nitrogen was injected to rapidly cool the material below 800°C, and the furnace was opened at 150°C to obtain a sintered substrate. The total time required for the sintering process was 22 hours. From this, 10 silicon nitride substrates were manufactured.

[0134] Comparative Example 1

[0135] A boron nitride slurry was spray-coated onto both sides of a silicon nitride sheet, and the solvent was evaporated to produce a silicon nitride sheet coated with 10 μm thick boron nitride particles. Ten of the produced silicon nitride sheets were stacked, placed in a boron nitride crucible, and maintained at 1930°C for 6 hours. After cooling, the furnace was opened at 150°C to obtain a sintered substrate. The total time required for the sintering process was 24 hours. From this, ten silicon nitride substrates were produced.

[0137] Comparative Example 2

[0138] A boron nitride slurry was spray-coated onto both sides of a silicon nitride sheet and the solvent was evaporated to produce a silicon nitride sheet coated with 10 μm thick boron nitride particles. Ten of the produced silicon nitride sheets were stacked, loaded into a boron nitride crucible, and maintained at 1930°C for 6 hours. Afterward, the first cooling zone was cooled at a rate of 10°C / min, the sheet was maintained at 1600°C for 1 hour, and the second cooling zone was cooled at a rate of 3.7°C / min. Below 800°C, the sheet was cooled by furnace cooling, and the furnace was opened at 150°C to obtain a sintered substrate. The total time required for the sintering process was 26 hours. From this, ten silicon nitride substrates were produced.

[0140] (Experimental Example)

[0141] Thermal conductivity and bending strength were measured using the equipment described below.

[0142] - Thermal Conductivity: Thermal Diffusivity Meter, LFA 467 Hyperflash_NETZSCH

[0143] - Bending strength measurement: Universal Testing Machine(UT<)_Instron

[0145] Bending measurement

[0146] The warping was measured non-contactually. A square silicon nitride substrate (140 mm × 190 mm × 0.32 mm) was scanned diagonally using a non-contact 3D measuring instrument. The warping value was defined as the ratio △Z / L (mm / mm), which is the difference between the lowest and highest points (△Z, mm) of one side of the silicon nitride substrate in the height direction from the sample holder, and the scanned diagonal length (L, mm).

[0148] The evaluation results of Examples 1-3 and Comparative Examples 1-2 are listed in Table 1.

[0150] Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Thermal conductivity (w / M·K) 78 79 82 84 81 Bending strength (MPa) 850 860 860 850 870 Bending amount (㎛ / mm) 7~10 4~8 < 2 < 2 < 2 Sintering process time (time) 24 26 24 26 22

[0152] When comparing the results of Examples 1-3 with those of Comparative Examples 1-2, it can be confirmed that Examples 1-3 are superior in thermal conductivity and bending strength, even though silicon nitride substrates were manufactured with similar sintering process times, and in particular, flatness of 2 μm / mm or less could be achieved. Comparative Example 1-2 did not form a silicon nitride sheet layer and applied silicon nitride particles, showing inferior results compared to Examples 1-3. In particular, although Comparative Example 2 attempted to improve bending characteristics by controlling the cooling rate, it was confirmed that while it was improved compared to Comparative Example 1, it did not reach the level of Examples 1-3 at all.

[0154] Although the present invention has been described above with reference to embodiments, the present invention is not limited by the embodiments disclosed in this specification, and it is obvious that various modifications can be made by a person skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration of the present invention were not explicitly described while describing the embodiments of the present invention above, it is natural to acknowledge that the effects predictable by said configuration should also be recognized. Explanation of the symbols

[0156] 1: Silicon nitride sheet 10: Boron nitride sheet layer 20: Silicon nitride sheet layer 100, 200: Green Sheet

Claims

Claim 1 A green sheet comprising a silicon nitride sheet layer and a boron nitride sheet layer laminated on one or both sides of the silicon nitride sheet layer, wherein the boron nitride sheet layer comprises a boron nitride sheet formed by sheet molding of boron nitride, and wherein the boron nitride sheet layer and the silicon nitride sheet layer are compressed to form a single sheet. Claim 2 delete Claim 3 In claim 1, the silicon nitride sheet layer comprises at least one silicon nitride sheet, and in the case where a plurality of silicon nitride sheets are included, the plurality of silicon nitride sheets are compressed into a green sheet. Claim 4 In claim 1, the boron nitride sheet layer is a green sheet comprising a biaxially oriented boron nitride sheet. Claim 5 In claim 1, the boron nitride sheet layer is a green sheet comprising a boron nitride sheet with a thickness of 10 μm to 20 μm. Claim 6 A method for manufacturing a silicon nitride substrate with suppressed warping, comprising: a step of interposing at least one green sheet according to claim 1 between an upper plate and a lower plate; a step of performing a degreasing process on the green sheet; a step of performing a sintering process on the green sheet; and a step of obtaining a silicon nitride substrate from the green sheet. Claim 7 In claim 6, the above green sheet is a method for manufacturing a silicon nitride substrate with suppressed bending, wherein a silicon nitride sheet layer and a boron nitride sheet layer are compressed. Claim 8 A method for manufacturing a silicon nitride substrate with suppressed bending, wherein, in claim 6, the silicon nitride sheet layer among the green sheets is constrained and sintered by the boron nitride sheet layer. Claim 9 In claim 6, a method for manufacturing a silicon nitride substrate with suppressed bending, wherein one or more green sheets are interposed. Claim 10 In claim 6, the silicon nitride sheet layer comprises at least one silicon nitride sheet, and in the case where a plurality of silicon nitride sheets are included, a method for manufacturing a silicon nitride substrate in which a plurality of silicon nitride sheets are compressed to suppress bending. Claim 11 In claim 9, a method for manufacturing a silicon nitride substrate with suppressed bending, wherein the boron nitride sheet layer is formed by compressing a plurality of boron nitride sheets with a thickness of 10 μm to 20 μm. Claim 12 In claim 6, the silicon nitride sheet is a method for manufacturing a silicon nitride substrate with suppressed warping formed by sheet molding from silicon nitride powder by tape casting. Claim 13 A method for manufacturing a silicon nitride substrate with suppressed warping according to claim 6, wherein the sintering process comprises a step of raising the temperature; a step of maintaining a predetermined temperature; and a step of cooling. Claim 14 A method for manufacturing a silicon nitride substrate with suppressed warping according to claim 13, wherein the cooling step is performed by leaving the green sheet undisturbed without separately performing a process for controlling the cooling temperature or cooling rate. Claim 15 A silicon nitride substrate manufactured according to the method for manufacturing a silicon nitride substrate with suppressed warping according to claim 6, wherein the diagonal length (L, mm) of the silicon nitride substrate manufactured in a rectangular shape is scanned by a non-contact 3D measuring instrument, and the difference (ΔZ, mm) between the lowest point and the highest point of one surface of the silicon nitride substrate is measured in the height direction from the sample holder, and the calculated value of the ratio of the measured diagonal length (L) to ΔZ, ΔZ / L (mm / mm), is 0.002 or less. Claim 16 In claim 15, a silicon nitride substrate comprising a sintered silicon nitride sheet layer and a sintered boron nitride sheet layer, wherein the sintered boron nitride sheet layer has a thickness of 10 μm to 20 μm. Claim 17 Silicon nitride substrate formed by constrained sintering of a green sheet according to claim 1. Claim 18 In claim 17, a silicon nitride substrate comprising a sintered boron nitride sheet layer, wherein the sintered boron nitride sheet layer has a thickness of 10 μm to 20 μm.

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