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

Abstract

The present invention relates to a green sheet, a method of manufacturing a silicon nitride substrate with reduced warpage, and a silicon nitride substrate manufactured thereby, and provides a green sheet comprising a silicon nitride sheet layer and a boron nitride sheet layer laminated on one or both surfaces of the silicon nitride sheet layer.

Description

Green sheet, method for manufacturing a silicon nitride substrate with suppressed warpage, and silicon nitride substrate manufactured therefrom

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

[0002] 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. Insulating ceramic substrates are being used to implement these circuit boards. Among insulating ceramic substrates, silicon nitride sintered substrates, in particular, are experiencing a rapid increase in use as insulating substrates for electric vehicle power modules due to their superior mechanical strength.

[0003] The purpose of the present invention is to provide a green sheet capable of manufacturing a ceramic sintered substrate having excellent flatness.

[0004] An object of the present invention is to provide a method for manufacturing a silicon nitride substrate capable of suppressing warpage and achieving excellent flatness.

[0005] The purpose of the present invention is to provide a silicon nitride substrate that can suppress warpage and achieve excellent flatness, thereby improving bonding strength with a metal thin film.

[0006] The objectives of the present invention are not limited to those mentioned above. Other objectives and advantages of the present invention not mentioned above can be understood through the following description and will be more clearly understood through the embodiments of the present invention. Furthermore, it will be readily apparent that the objectives and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0007] 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.

[0008] The above silicon nitride sheet layer and the above boron nitride sheet layer may be compressed.

[0009] The above silicon nitride sheet layer comprises at least one silicon nitride sheet, and when it comprises a plurality of silicon nitride sheets, it may be a plurality of silicon nitride sheets pressed together.

[0010] The above boron nitride sheet layer may include a biaxially oriented boron nitride sheet.

[0011] The above boron nitride sheet layer may include a boron nitride sheet having a thickness of 10 μm to 20 μm.

[0012]

[0013] In one embodiment of the present invention,

[0014] A step of interposing at least one green sheet between the upper plate and the lower plate;

[0015] A step of performing a degreasing process on the above green sheet;

[0016] A step of performing a sintering process on the above green sheet; and

[0017] A step of obtaining a silicon nitride substrate from the above green sheet;

[0018] A method for manufacturing a silicon nitride substrate with suppressed warpage is provided.

[0019] In the above method, the green sheet can be formed by compressing a silicon nitride sheet layer and a boron nitride sheet layer.

[0020] In the above method, the silicon nitride sheet layer among the green sheets can be constrained and sintered by the boron nitride sheet layer.

[0021] In the above method, one or more green sheets may be provided.

[0022] In the above method, the silicon nitride sheet layer includes at least one silicon nitride sheet, and when it includes a plurality of silicon nitride sheets, the plurality of silicon nitride sheets may be compressed.

[0023] In the above method, the boron nitride sheet layer may be formed by pressing a plurality of boron nitride sheets having a thickness of 10 μm to 20 μm.

[0024] In the above method, the silicon nitride sheet can be formed into a sheet by tape casting from silicon nitride powder.

[0025] The above sintering process

[0026] step of heating;

[0027] a step of maintaining a predetermined temperature; and

[0028] A cooling step may be included.

[0029] The above cooling step can be performed by leaving the green sheet alone without performing a separate process of controlling the cooling temperature or cooling rate.

[0030]

[0031] 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 warpage, wherein a diagonal length (L, mm) of the silicon nitride substrate manufactured in a square shape is scanned with a non-contact three-dimensional measuring device, and a difference (ΔZ, mm) between the lowest point and the highest point of one side of the silicon nitride substrate in the height direction from the sample holder is measured, and a ratio of the measured diagonal length (L) and ΔZ, ΔZ / L (mm / mm), is calculated to be 0.002 or less.

[0032] The above silicon nitride substrate includes 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.

[0033] The above silicon nitride substrate may be formed by constrained sintering of a compressed silicon nitride sheet layer and a boron nitride sheet layer.

[0034] The above silicon nitride substrate includes a sintered boron nitride sheet layer, and the sintered boron nitride sheet layer may have a thickness of 10 μm to 20 μm.

[0035] According to the present invention, a silicon nitride substrate capable of suppressing warpage and producing a circuit board having excellent flatness when bonding metal thin films can be manufactured.

[0036] In addition to the effects described above, specific effects of the present invention are described below while explaining specific details for carrying out the invention.

[0037] Figure 1 is a cross-sectional view of the green sheet according to one embodiment.

[0038] Figure 2 is a cross-sectional view of the green sheet according to another embodiment.

[0039] Figure 3 is a schematic diagram schematically showing a silicon nitride sheet layer among green sheets according to one embodiment.

[0040] Figure 4 is a schematic diagram schematically showing a green sheet according to one embodiment formed by laminating a boron nitride sheet layer and the silicon nitride sheet layer.

[0041] Figure 5 is a flow chart of a method for manufacturing the above-mentioned warpage-suppressed silicon nitride substrate.

[0042] The above-described objects, features, and advantages will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily practice the technical idea of ​​the present invention. In describing the present invention, if it is determined that a detailed description of known technologies related to the present invention may unnecessarily obscure the gist of the present invention, a detailed description thereof will be omitted. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to indicate the same or similar components.

[0043] Hereinafter, the phrase "any configuration is placed on (or below)" a component or "on (or below)" a component may mean that any configuration is placed in contact with the upper surface (or lower surface) of said component, and that other configurations may be interposed between said component and any configuration placed on (or below) said component.

[0044] Additionally, when it is described that a component is "connected," "coupled," or "connected" to another component, it should be understood that the components may be directly connected or connected to one another, but that other components may also be "interposed" between the components, or that each component may be "connected," "coupled," or "connected" through another component.

[0045] 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.

[0046] In this specification, a 'green sheet' is a laminated sheet in which sheets formed from a ceramic material are laminated by a lamination process, and are subject to a sintering process, and a ceramic sintered substrate (referred to as a silicon nitride substrate in this specification) can be formed by the sintering process.

[0047] Figure 1 is a cross-sectional view of the green sheet (100) according to one embodiment.

[0048] Figure 1 shows a green sheet in which the boron nitride sheet layer (10) is formed on one surface of the silicon nitride sheet layer (20).

[0049] Figure 2 is a cross-sectional view of the green sheet (200) according to another embodiment.

[0050] Figure 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).

[0051] The above silicon nitride sheet layer (20) includes at least one silicon nitride sheet (1), and when it includes a plurality of silicon nitride sheets (1), a plurality of silicon nitride sheets (1) can be formed by pressing them together.

[0052] The above green sheet (100, 200) can be suppressed from warping as the silicon nitride sheet layer (20) is restrained and sintered by the boron nitride sheet layer (10) during the sintering process, and accordingly, a silicon nitride substrate with suppressed warping can be manufactured from the above green sheet (100, 200).

[0053] The existing boron nitride powder was applied to the green sheet as a release agent, but the green sheet (100, 200) forms the boron nitride sheet layer (10) instead of applying the boron nitride powder.

[0054] The above green sheet (100, 200) can manufacture a ceramic sintered substrate with excellent flatness. To function as a circuit board, a copper film is bonded to a ceramic substrate, such as a silicon nitride substrate, and a semiconductor device is die-attached on the copper film to operate. Since the semiconductor device operates under high voltage, the heat generated at this time is very high, and the heat generated per unit area can reach 30 times that of an electric iron. This rapid heat generation also transfers heat to the copper film and the ceramic substrate, and at this time, due to the different coefficients of thermal expansion of the copper film and the ceramic substrate, the heterogeneous bonding surface of the copper film and the ceramic substrate may delaminate, ultimately causing a problem of lowering the reliability of the circuit board. Therefore, the heterogeneous bonding strength of the copper film and the ceramic substrate is a key material property that ensures 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 film. If the flatness of the ceramic substrate falls below a certain standard, the bonding strength between the copper film and the ceramic substrate deteriorates, ultimately lowering the reliability of the circuit board product.

[0055] 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.

[0056] Since the ceramic substrate obtained by sintering an existing green sheet is thin, and since shrinkage occurs when a green sheet formed of a ceramic material such as silicon nitride powder is sintered and transformed into a ceramic substrate, warpage deformation occurs in the thin ceramic substrate after sintering. Since this warpage deformation (or reduction in flatness) causes a decrease in bonding strength when bonding copper thin films, the warpage deformation must be controlled below a certain standard. The green sheet (100, 200) can have its warpage deformation controlled below a certain standard during sintering.

[0057] The above silicon nitride sheet layer (20) includes at least one silicon nitride sheet (1), and when it includes a plurality of silicon nitride sheets, it may be a plurality of silicon nitride sheets pressed together.

[0058] The above silicon nitride sheet (1) can be formed by sheet molding from silicon nitride powder by tape casting. Hereinafter, a process for molding the above silicon nitride sheet (1) will be specifically described as an example.

[0059] A slurry may be prepared by mixing silicon nitride powder, a ceramic additive, a solvent, optionally a dispersant, optionally a binder, and optionally a plasticizer, and then the slurry may be molded to form a silicon nitride sheet (1). The solvent may be an organic solvent, and for example, at least one selected from ethanol, isopropyl alcohol, toluene, and the like may be used. The ceramic additive may include at least one selected from yttrium oxide (Y2O3), magnesium oxide (MgO), zirconium oxide, and the like. For the slurry, tape casting may be performed, for example, to obtain the silicon nitride sheet (1) molded into a sheet. A commercially available dispersant may be used as the dispersant, and for example, BYK-111, a type of ester block copolymer manufactured by BYK Chemie of Germany, may be used. The binder may include, for example, polyvinyl butyral (PVB). The plasticizer may include, for example, dibutyl phthalate or dioctyl phthalate.

[0060] The slurry containing silicon nitride powder can be aged to remove volatile gases from the slurry. During the aging process, the slurry can be stirred using a stirrer. The aging process can be performed for about 24 hours.

[0061] The slurry prepared as described above can be molded using a tape casting process to form the silicon nitride sheet (1). Specifically, the tape casting process can be performed by pouring the slurry onto a blade set to a constant dam height and applying the slurry onto a moving substrate film. The solvent can be evaporated from the slurry applied onto the substrate film and removed, thereby obtaining a molded body of the silicon nitride sheet (1). The substrate film can be a stainless steel tape, an oil-based paper tape, or a polymer tape such as polyester. For example, the slurry can be poured onto a doctor blade set to a dam height of about 0.3 mm and the slurry can be applied onto a substrate film moving at a predetermined speed (e.g., 0.1 m / min to 1 m / min). Thereafter, a drying process and a process of removing the substrate film can be performed to obtain the silicon nitride sheet (1).

[0062] The tape casting process can be performed at a temperature of 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.

[0063] The above silicon nitride sheet (1) may have a size of M × N. For example, each of M and N may be from 60 mm to 300 mm, but is not particularly limited. That is, each of M and N may be changed depending on the size of the silicon nitride substrate to be finally manufactured.

[0064] Although the method for manufacturing the above silicon nitride sheet (1) has been described as an example, it is not limited thereto, and it can be manufactured according to a known method to implement the desired properties or to suit the intended use.

[0065]

[0066] Figure 3 is a schematic diagram schematically showing the silicon nitride sheet layer (20) formed by laminating a plurality of silicon nitride sheets (1) by pressing.

[0067] A plurality of silicon nitride sheets (1) manufactured as described above can be laminated. A lamination process can be performed on the laminate of a plurality of silicon nitride sheets (1), thereby forming 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.

[0068] The above silicon nitride sheet layer (20) can be formed by pressing. The pressing process performed on the silicon nitride sheet layer (20) can utilize a warm isostatic press (WIP). The pressing process can 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) can be 0.3 mm to 4 mm.

[0069] The above silicon nitride sheet layer (20) is formed by overlapping the silicon nitride sheets (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.

[0070]

[0071] Separately from the above silicon nitride sheet layer (20), the above boron nitride sheet layer (10) is manufactured. The above boron nitride sheet layer (10) can be formed into a sheet by tape casting from boron nitride powder.

[0072] The above green sheet (100, 200) is formed into 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 into 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 a state in which, when boron nitride particles are applied as a release agent to the green sheet or spray-applied in the form of a slurry, the applied boron nitride particles are simply placed on the silicon nitride sheet layer (20).

[0073] The above green sheet (100, 200) can be manufactured into a substrate by performing a sintering process. In the process of sintering the green sheet (100, 200), the silicon nitride sheet layer (20) shrinks due to particle densification, but the boron nitride sheet layer (10) shrinks less or does not shrink. Since 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) pressed onto the boron nitride sheet layer (10) acts as a restraining force when the silicon nitride sheet layer (20) shrinks, so that a uniform shrinkage force is applied to the entire silicon nitride substrate manufactured, thereby suppressing warpage of the sintered body after sintering.

[0074]

[0075] In the silicon nitride substrate obtained by sintering the above green sheet (100, 200), since the silicon nitride sheet layer (20) experiences more shrinkage due to densification than the boron nitride sheet layer (10), one side of the silicon nitride sheet layer (20) may have a smaller size than the boron nitride sheet layer (10).

[0076] In one embodiment, the boron nitride sheet layer (10) may include a boron nitride sheet having 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, so that the silicon nitride sheet layer (20) may be formed into a sintered body in which the silicon nitride sheet layer (20) is appropriately densified while appropriately providing binding force to the green sheet (10) during sintering.

[0077] In one embodiment, the silicon nitride sheet layer (20) may be formed using a single sheet-formed boron nitride sheet to manufacture the green sheet (100, 200).

[0078] The above boron nitride sheet can be formed by a method similar to the method of forming a sheet by tape casting silicon nitride powder from the above silicon nitride sheet (1). For example, after preparing a slurry containing boron nitride powder instead of silicon nitride, the slurry can be applied onto a substrate film, and then a solvent can be evaporated from the slurry to obtain a molded body of the boron nitride sheet. Hereinafter, a process for forming the boron nitride sheet will be specifically described by way of example.

[0079] A slurry may be prepared by mixing boron nitride powder, a binder, a solvent, optionally a dispersant, optionally a plasticizer, etc., and then the slurry may be molded to form a boron nitride sheet. In one embodiment, the slurry may include 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. For the slurry, for example, tape casting may be performed to obtain a sheet-molded boron nitride sheet.

[0080] The above boron nitride sheet layer (10) can be biaxially oriented. As described above, in order to form the boron nitride sheet layer (10), a boron nitride sheet is first formed and then pressed 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 be biaxially oriented. Since the boron nitride particles used in the manufacture of the boron nitride sheet may be, for example, non-spherical particles having an aspect ratio, specifically, flake-shaped particles, the boron nitride particles can be biaxially oriented when the sheet is formed by a process such as tape casting. This can be contrasted with the case where the applied boron nitride particles are formed in a non-oriented manner when applied as a release agent to a green sheet or when made into a slurry and spray-applied. In the biaxially oriented boron nitride sheet layer (10), for example, elongated flake-shaped powders are arranged to be connected to each other, i.e., oriented, so that the cohesion between the powders is good and uniform heat can be transferred to the silicon nitride sheet layer (20). In this way, the more uniform the heat transfer, the more the obtained green sheet (100, 200) can have improved properties including warpage.

[0081]

[0082] Figure 4 is a schematic diagram schematically showing a green sheet (100) formed by laminating the boron nitride sheet layer (10) and the silicon nitride sheet layer (20).

[0083] The boron nitride sheet layer (10) obtained as described above can be laminated on at least one surface of the silicon nitride sheet layer (20), and then pressed and attached to form the green sheet (100, 200). The process of laminating and pressing the boron nitride sheet layer (10) on the silicon nitride sheet layer (20) can utilize, for example, an isostatic hydraulic press.

[0084]

[0085] In one embodiment of the present invention,

[0086] A step of interposing at least one green sheet between the upper plate and the lower plate;

[0087] A step of performing a degreasing process on the above green sheet;

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

[0089] A step of obtaining a silicon nitride substrate from the above green sheet;

[0090] A method for manufacturing a silicon nitride substrate with suppressed warpage is provided.

[0091] Fig. 5 is a flowchart of a method for manufacturing the above-described warpage-suppressed silicon nitride substrate. Referring to Fig. 5, the method for manufacturing the above-described warpage-suppressed silicon nitride substrate may include a step (S10) of interposing at least one green sheet (100, 200) between an upper plate and a lower plate, a step (S20) of performing a degreasing process on the green sheet (100, 200), a step (S30) of performing a sintering process on the green sheet (100, 200), and a step (S40) of obtaining a silicon nitride substrate from the green sheet (100, 200).

[0092] Although only one green sheet (100, 200) may be interposed between the upper plate and the lower plate, a laminated structure in which multiple green sheets (100, 200) are laminated can be formed in order to simultaneously perform sintering on multiple green sheets (100, 200). The laminated structure in which multiple green sheets (100, 200) are laminated can be formed by stacking multiple green sheets (100, 200) as they are without performing an additional pressing process. By forming the laminated structure in this way, a sintering process can be performed on multiple green sheets (100, 200) simultaneously, so that multiple silicon nitride substrates can be manufactured in a single process. Among the green sheets (100, 200), the boron nitride sheet layer (10) prevents agglomeration between multiple silicon nitride substrates after sintering.

[0093] The above-mentioned manufactured silicon nitride substrate can be manufactured in a state in which the boron nitride sheet layer (10) is pressed onto the silicon nitride sheet layer (20).

[0094] In this specification, a 'silicon nitride substrate' is a substrate including a sintered silicon nitride sheet layer, which may also include the sintered boron nitride sheet layer.

[0095] 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.

[0096] 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, a plurality of said green sheets (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.

[0097]

[0098] A debinding process (Binder Burn Out, BBO) can be performed on the green sheet (100, 200) prepared as described above or a laminated structure including the same. As a result, organic substances such as binders, dispersants, and plasticizers within the green sheet (100, 200) can all be removed by incineration. In one embodiment, the debinding process can be performed at a predetermined temperature under atmospheric pressure for about 30 to 100 hours. For example, the debinding process can be performed under the atmosphere (air). For example, the debinding process can be performed in an atmospheric furnace (AF) at a temperature of about 600°C for about 30 hours.

[0099]

[0100] A sintering process can be performed on the above-degreased green sheet (100, 200) or the laminated structure including the same. Following the degreased process, the green sheet (100, 200) or the laminated structure including the same can be provided in a crucible. By placing a bedding powder in the crucible, the green sheet (100, 200) or the laminated structure including the same can be buried in the bedding powder. The bedding powder can include boron nitride powder, silicon nitride powder, or a mixture thereof. When the bedding powder includes a mixture of boron nitride powder and silicon nitride powder, the boron nitride powder and the silicon nitride powder can be mixed in a 1:1 ratio.

[0101] By heating the crucible, a sintering process can be performed on the green sheet (100, 200) or a laminated structure including the same. As a result, the green sheet (100, 200) can be constrained and sintered, thereby forming a silicon nitride substrate.

[0102]

[0103] The above sintering process

[0104] step of heating;

[0105] a step of maintaining a predetermined temperature; and

[0106] A cooling step may be included.

[0107] In one embodiment, the sintering process may be performed by heating to a temperature of 1700°C to 2000°C and then maintaining the temperature for 6 to 12 hours. For example, the sintering process may be performed by heating to a temperature of about 1900°C and then maintaining the temperature for about 6 hours. Subsequently, the cooling step may be performed by leaving the laminated structure alone without separately performing a process of controlling the cooling temperature or controlling the cooling rate. For example, the cooling step may be performed by leaving the green sheet (100, 200) or the laminated structure including the same in a sintering furnace and rapidly cooling it.

[0108] The method for manufacturing the above-mentioned warpage-suppressed silicon nitride substrate is performed by sintering a green sheet (100, 200) in which a boron nitride sheet layer (10) is attached to a silicon nitride sheet layer (20), thereby restraining and sintering the silicon nitride sheet layer (20) by the boron nitride sheet layer (10), thereby manufacturing the silicon nitride substrate, so that warpage is suppressed. Therefore, additional control of the cooling temperature or cooling rate during cooling during the sintering process may not be required to suppress warpage.

[0109] In order to sinter the silicon nitride sheet layer (20), it is necessary to raise the sintering temperature and then maintain it for a certain period of time. The sintering temperature within the above range is suitable for producing a dense sintered body by ensuring that the silicon nitride particles grow and rearrange to achieve appropriate densification while preventing excessive volatilization of the sintering agent. However, the process of raising the temperature of 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 requires a long time, so a long operating time in the sintering process immediately 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 implement the physical properties of the product. Therefore, reducing the cooling time may be advantageous in reducing the sintering process time. In the past, it was necessary to control the cooling speed because the warpage of the substrate increased when cooling was performed quickly for a certain period of time, but the method for manufacturing the silicon nitride substrate with suppressed warpage can obtain a sintered body with controlled warpage of the substrate without intentionally slowing down the cooling speed, and rather, can reduce the time of the sintering process and thereby increase productivity.

[0110] The above sintering process can be performed in a nitrogen atmosphere. After sintering the green sheet (100, 200) or the laminated structure including the same, a silicon nitride substrate derived from the individual green sheets (100, 200) can be obtained.

[0111]

[0112] Among the silicon nitride substrates, the layer resulting from the silicon nitride sheet layer (20) may have a size of M × N and may have a smaller size than the layer resulting from the boron nitride sheet layer (10). For example, each of M and N may be 40 mm to 200 mm. The size of the layer resulting from the silicon nitride sheet layer (20) among the silicon nitride substrates may shrink during the sintering process and become smaller than the size of the green sheets (100, 200).

[0113] A silicon nitride substrate manufactured by the method for manufacturing a silicon nitride substrate with suppressed warpage can exhibit excellent flatness as it is manufactured with suppressed warpage.

[0114] In one embodiment, a silicon nitride substrate manufactured according to the method for manufacturing a silicon nitride substrate with suppressed warpage can realize a flatness of 0.002 or less, whereby a diagonal length (L, mm) of the silicon nitride substrate manufactured in a square shape is scanned with a non-contact three-dimensional measuring device, and a difference (ΔZ, mm) between the lowest point and the highest point of one side of the silicon nitride substrate in the height direction from the sample support is measured, and a ratio of the measured diagonal length (L) and ΔZ, ΔZ / L (mm / mm), is calculated.

[0115] The above silicon nitride substrate can be used as an insulating ceramic substrate for circuit boards. In one embodiment, the above silicon nitride substrate can be used as an insulating substrate for a power module for an electric vehicle.

[0116]

[0117] In one embodiment of the present invention, a silicon nitride substrate is provided, which is manufactured according to a method for manufacturing a silicon nitride substrate with suppressed warpage, wherein the diagonal length (L, mm) of the silicon nitride substrate manufactured in a square shape is scanned with a non-contact three-dimensional measuring device, and the difference (ΔZ, mm) between the lowest point and the highest point of one side of the silicon nitride substrate in the height direction from the sample holder is measured, and the ratio of the measured diagonal length (L) to ΔZ, ΔZ / L (mm / mm), is calculated and has a value of 0.002 or less. Since the boron nitride sheet layer included in the green sheet is sintered, the silicon nitride substrate includes 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 include a boron nitride sheet having a thickness of 10 μm to 20 μm.

[0118]

[0119] In one embodiment of the present invention, a silicon nitride substrate is provided in which a compressed silicon nitride sheet layer (20) and a boron nitride sheet layer are constrained and sintered to form a silicon nitride substrate. The silicon nitride substrate can be manufactured according to the method for manufacturing a silicon nitride substrate with suppressed warpage described above. Since the boron nitride sheet layer included in the green sheet is sintered, the silicon nitride substrate includes a sintered boron nitride sheet layer, and the sintered boron nitride sheet layer can have a thickness of 10 μm to 20 μm. The sintered boron nitride sheet layer can include a boron nitride sheet having a thickness of 10 μm to 20 μm.

[0120]

[0121] Hereinafter, examples and comparative examples of the present invention will be described. The following examples are merely exemplary of the present invention, and the present invention is not limited to the examples described below.

[0122]

[0123] (Example)

[0124] Example 1

[0125] A 15-μm-thick boron nitride sheet was laminated on one side of a silicon nitride sheet, and the boron nitride sheet and the silicon nitride sheet were pressed together using an isostatic hydraulic press at 70°C and 30 MPa for 15 minutes. After stacking 10 pressed green sheets, they were loaded into a boron nitride crucible and maintained at 1930°C for 6 hours, then cooled and the furnace was opened at 150°C to obtain a sintered body substrate. The sintering process took a total of 24 hours. From this, 10 silicon nitride substrates were manufactured.

[0126]

[0127] Example 2

[0128] A 15-μm-thick boron nitride sheet was laminated on one side of a silicon nitride sheet, and the boron nitride sheet and the silicon nitride sheet were pressed together using an isostatic hydraulic press at 70°C and 30 MPa for 15 minutes. After stacking 10 pressed green sheets, they were 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, they were maintained at 1600°C for 1 hour, cooled at a rate of 3.7°C / min in the second cooling zone, and cooled by furnace below 800°C, and the furnace was opened at 150°C to obtain a sintered body substrate. The sintering process took a total of 26 hours. From this, 10 silicon nitride substrates were manufactured.

[0129]

[0130] Example 3

[0131] A 15-μm-thick boron nitride sheet was laminated on one side of a silicon nitride sheet, and the boron nitride sheet and the silicon nitride sheet were pressed together using an isostatic hydraulic press at 70°C and 30 MPa for 15 minutes. After stacking 10 pressed green sheets, they were loaded into a boron nitride crucible and maintained at 1930°C for 6 hours, then cooled in a furnace, and when the temperature was below 800°C, a large amount of nitrogen was injected to rapidly cool them, and the furnace was opened at 150°C to obtain a sintered body substrate. The sintering process took a total of 22 hours. From this, 10 silicon nitride substrates were manufactured.

[0132]

[0133] Comparative Example 1

[0134] A boron nitride slurry was sprayed 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 manufactured silicon nitride sheets were stacked, loaded into a boron nitride crucible, and maintained at 1930°C for 6 hours, then cooled in a furnace and opened at 150°C to obtain a sintered body substrate. The sintering process took a total of 24 hours. From this, 10 silicon nitride substrates were manufactured.

[0135]

[0136] Comparative Example 2

[0137] A boron nitride slurry was sprayed 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 manufactured silicon nitride sheets were stacked, loaded into a boron nitride crucible, and maintained at 1930°C for 6 hours. The first cooling zone was cooled at a rate of 10°C / min, and the crucible was maintained 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 body substrate. The sintering process took a total of 26 hours. From this, 10 silicon nitride substrates were manufactured.

[0138]

[0139] (Experimental example)

[0140] Thermal conductivity and bending strength were measured using the equipment described below.

[0141] - Thermal conductivity: Thermal diffusivity meter, LFA 467 Hyperflash_NETZSCH

[0142] - Bending strength measurement: Universal Testing Machine(UT<)_Instron

[0143]

[0144] bending measurement

[0145] Warpage was measured using a non-contact method. A square silicon nitride substrate (140 mm × 190 mm × 0.32 mm) was scanned in the diagonal direction of the silicon nitride substrate using a non-contact 3D measuring device. The ratio of the scanned diagonal length (L, mm) and the difference between the lowest and highest points (△Z, mm) on one side of the silicon nitride substrate in the height direction from the sample support, △Z / L (mm / mm), was defined as the warpage value.

[0146]

[0147] The evaluation results of Example 1-3 and Comparative Example 1-2 are shown in Table 1.

[0148]

[0149] Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Thermal Conductivity (w / M·K) 7879828481 Bending Strength (MPa) 850860860850870 Deflection (㎛ / mm) 7~104~8 < 2< 2< 2 Sintering Process Time (hours) 2426242622

[0150] When the results of Example 1-3 are compared with the results of Comparative Example 1-2, it can be confirmed that Example 1-3 has superior thermal conductivity and bending strength even though the silicon nitride substrate was manufactured with a similar sintering process time, and in particular, it was able to achieve a flatness of 2㎛ / mm or less. Comparative Example 1-2 showed inferior results to Example 1-3 in that the silicon nitride sheet layer was not formed and silicon nitride particles were applied. In particular, although the bending characteristics were improved by controlling the cooling rate in Comparative Example 2, it was confirmed that it was not at all as good as Example 1-3, although it was improved compared to Comparative Example 1.

[0151]

[0152] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the exemplary embodiments disclosed herein, and that various modifications may be made by those skilled in the art within the scope of the technical spirit of the invention. Furthermore, even if the operational effects of the configurations of the invention have not been explicitly described and explained while describing the exemplary embodiments of the invention, it is also to be understood that the effects predictable by the configurations should be acknowledged.

[0153]

[0154] [Explanation of symbols]

[0155] 1: Silicon nitride sheet

[0156] 10: Boron nitride sheet layer

[0157] 20: Silicon nitride sheet layer

[0158] 100, 200: Green Sheet

Claims

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.

2. In paragraph 1, The above silicon nitride sheet layer and the above boron nitride sheet layer are pressed Green sheet.

3. In paragraph 1, The above 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 are pressed. Green sheet.

4. In paragraph 1, The above boron nitride sheet layer comprises a biaxially oriented boron nitride sheet. Green sheet.

5. In paragraph 1, The above boron nitride sheet layer comprises a boron nitride sheet having a thickness of 10 μm to 20 μm. Green sheet.

6. A step of interposing at least one green sheet according to claim 1 between the upper plate and the lower plate; A step of performing a degreasing process on the above green sheet; A step of performing a sintering process on the above green sheet; and A step of obtaining a silicon nitride substrate from the above green sheet; A method for manufacturing a silicon nitride substrate with suppressed warpage.

7. In paragraph 6, The above green sheet is formed by pressing a silicon nitride sheet layer and a boron nitride sheet layer. A method for manufacturing a silicon nitride substrate with suppressed warpage.

8. In paragraph 6, Among the above green sheets, the silicon nitride sheet layer is constrained and sintered by the boron nitride sheet layer. A method for manufacturing a silicon nitride substrate with suppressed warpage.

9. In paragraph 6, The above green sheet is interposed in one or more A method for manufacturing a silicon nitride substrate with suppressed warpage.

10. In paragraph 6, The above 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 are pressed. A method for manufacturing a silicon nitride substrate with suppressed warpage.

11. In paragraph 9, The above boron nitride sheet layer is formed by pressing multiple boron nitride sheets having a thickness of 10 μm to 20 μm. A method for manufacturing a silicon nitride substrate with suppressed warpage.

12. In paragraph 6, The above silicon nitride sheet is formed into a sheet by tape casting from silicon nitride powder. A method for manufacturing a silicon nitride substrate with suppressed warpage.

13. In paragraph 6, The above sintering process step of heating; a step of maintaining a predetermined temperature; and a cooling step; including A method for manufacturing a silicon nitride substrate with suppressed warpage.

14. In paragraph 13, The above cooling step is performed by leaving the green sheet alone without performing a separate process of controlling the cooling temperature or cooling speed. A method for manufacturing a silicon nitride substrate with suppressed warpage.

15. A silicon nitride substrate manufactured according to a method for manufacturing a silicon nitride substrate with suppressed warpage according to Article 6, wherein the diagonal length (L, mm) of the silicon nitride substrate manufactured in a square shape is scanned with a non-contact 3D measuring device, and the difference (ΔZ, mm) between the lowest point and the highest point of one side of the silicon nitride substrate in the height direction from the sample stand is measured, and the ratio of the measured diagonal length (L) and ΔZ, ΔZ / L (mm / mm), is calculated to be 0.002 or less.

16. In paragraph 15, A sintered silicon nitride sheet layer and a sintered boron nitride sheet layer are included, wherein the sintered boron nitride sheet layer has a thickness of 10 μm to 20 μm. Silicon nitride substrate.

17. A silicon nitride substrate formed by constrained sintering of a compressed silicon nitride sheet layer and a boron nitride sheet layer.

18. In paragraph 17, A sintered boron nitride sheet layer comprising a sintered boron nitride sheet layer having a thickness of 10 μm to 20 μm. Silicon nitride substrate.

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