A sintered body includes a crystal grain containing silicon nitride, and a grain boundary phase. If dielectric losses of the sintered body are measured while applying an alternating voltage to the sintered body and continuously changing a frequency of the alternating voltage from 50 Hz to 1 MHz, an average value ε.sub.A of dielectric losses of the sintered body in a frequency band from 800 kHz to 1 MHz and an average value ε.sub.B of dielectric losses of the sintered body in a frequency band from 100 Hz to 200 Hz satisfy an expression |ε.sub.A−ε.sub.B|≤0.1.

A metal-ceramic substrate (1) comprising an insulating layer (11) comprising a ceramic and having a first thickness (D1), and a metallization layer (12) bonded to the insulation layer (11) and having a second thickness (D2),
wherein the first thickness (D1) is less than 250 μm and the second thickness (D2) is greater than 200 μm and wherein the first thickness (D1) and the second thickness (D2) are dimensioned such that a ratio of an amount of the difference between a thermal expansion coefficient of the metallization layer (12) and a thermal expansion coefficient of the metal-ceramic substrate (1) to a thermal expansion coefficient of the metal-ceramic substrate (1)
has a value less than 0.25, preferably less than 0.2 and more preferably less than 0.15 or even less than 0.1.

An electrostatic chuck includes a ceramic top plate layer made of a beryllium oxide material, a ceramic bottom plate layer made of a beryllium oxide material, a ceramic middle plate layer disposed between the ceramic top plate layer and the ceramic bottom plate layer, an electrode layer disposed between the ceramic top plate layer and the ceramic middle plate layer, and a heater layer disposed between the ceramic middle plate layer and the ceramic bottom plate layer. The electrode layer joins and hermetically seals the ceramic top plate layer to the ceramic middle plate layer, and the heater layer joins and hermetically seals the ceramic middle plate layer to the ceramic bottom plate layer.

A bonded body of the present invention includes a ceramic member formed of ceramics and a Cu member formed of Cu or a Cu alloy. In a bonding layer formed between the ceramic member and the Cu member, an area ratio of a Cu.sub.3P phase in a region extending by up to 50 μm toward the Cu member side from a bonding surface of the ceramic member is equal to or lower than 15%.

A power-module substrate and a heat sink made of an aluminum-impregnated silicon carbide formed by impregnating aluminum in a porous body made of silicon carbide; where yield strength of a circuit layer is σ1 (MPa), a thickness of the circuit layer is t1 (mm), a bonding area of the circuit layer and a ceramic board is A1 (mm.sup.2), yield strength of a metal layer is σ2 (MPa), a thickness of the metal layer is t2 (mm), a bonding area of the metal layer and the ceramic board is A2 (mm.sup.2); the thickness t1 is formed to be between 0.1 mm and 3.0 mm (inclusive); the thickness t2 is formed to be between 0.15 mm and 5.0 mm (inclusive); the thickness t2 is formed larger than the thickness t1; and a ratio {(σ2×t2×A2)/(σ1×t1×A1)} is in a range between 1.5 and 15 (inclusive).

Method of manufacturing a metal-ceramic substrate (1) which, in the finished state, has a ceramic layer (11) and a metal layer (12) extending along a main extension plane (HSE) and arranged one above the other along a stacking direction (S) extending perpendicularly to the main extension plane (HSE) comprising providing the metal layer (12) and the ceramic layer (11) and bonding the metal layer (12) to the ceramic layer (11) in regions to form a first region (B1), which has a materially bonded connection between the metal layer (12) and the ceramic layer (11), and a second region (B2), in which the metal layer (12) and the ceramic layer (11) are arranged one above the other without a materially bonded connection, as seen in the stacking direction (S).

The bonded substrate includes the silicon nitride ceramic substrate, a copper plate, the bonding layer, and penetrating regions. The copper plate and the bonding layer are patterned into a predetermined shape, and are disposed over a main surface of the silicon nitride ceramic substrate. The bonding layer bonds the copper plate to the main surface of the silicon nitride ceramic substrate. The penetrating regions each include one or more penetrating portions penetrating continuously from the main surface of the substrate into the silicon nitride ceramic substrate to a depth of 3 μm or more and 20 μm or less, and contain silver, and the number of penetrating regions present per square millimeter of the main surface of the substrate is one or more and 30 or less.

A bonded substrate includes a ceramic substrate, a copper plate, and a bonding layer. The ceramic substrate has a main surface having a flat region having a maximum height Rz of 10 μm or less. The ceramic substrate has a particle-defect hole being exposed to the main surface, imparting flatness lower than flatness of the flat region to a part of the main surface, and having a depth of 10 μm or more and 60 μm or less. The copper plate includes a first portion disposed over the flat region and a second portion filling the particle-defect hole. The bonding layer includes a third portion covering the flat region and a fourth portion filling the particle-defect hole, and the second portion and the fourth portion fill 80% or more of a volume of the particle-defect hole. The bonding layer bonds the copper plate to the main surface.

A bonded body of the present invention includes a ceramic member formed of ceramics and a Cu member formed of Cu or a Cu alloy. In a bonding layer formed between the ceramic member and the Cu member, an area ratio of a Cu.sub.3P phase in a region extending by up to 50 μm toward the Cu member side from a bonding surface of the ceramic member is equal to or lower than 15%.

A silicon nitride circuit board includes a silicon nitride substrate, a first copper layer over one surface of the silicon nitride substrate, and a second copper layer over the other surface of the silicon nitride substrate, in which a fracture toughness value Kc of the silicon nitride substrate is equal to or more than 5.0 MPa.Math.m.sup.0.5 and equal to or less than 10.0 MPa.Math.m.sup.0.5, and when a coefficient of linear expansion of the silicon nitride substrate is α.sub.B (/° C.), a Young's modulus of the silicon nitride substrate is E.sub.B (GPa), a coefficient of linear expansion of the first copper layer is α.sub.A (/° C.), and a coefficient of linear expansion of the second copper layer is α.sub.C (/° C.), each of a heat shock parameter HS1 and a heat shock parameter HS2 is equal to or more than 1.30 GPa and equal to or less than 2.30 GPa.