JP4738291B2 - Metallized ceramic substrate manufacturing method, aluminum nitride substrate manufacturing method, and aluminum nitride substrate - Google Patents

Description

  The present invention relates to a method of manufacturing a metallized ceramic substrate in which a metal layer that becomes a wiring pattern is formed on the surface of an aluminum nitride substrate.

  Aluminum nitride substrates have excellent characteristics such as high thermal conductivity and high thermal shock resistance, and are widely used as various electronic circuit board materials such as submounts for mounting semiconductor devices, substrates for power modules, etc. Yes.

  When an aluminum nitride substrate is used as an electronic circuit substrate, it is necessary to form a metal layer on the surface to form electrodes and circuit patterns. However, aluminum nitride has a problem that its bonding property to metal is lower than that of alumina, and various devices have been made to form a metal layer bonded to the surface of an aluminum nitride substrate with high bonding strength.

  On the other hand, a method of oxidizing the surface of an aluminum nitride substrate and forming a metal layer on the obtained oxide film is also known. When an oxide film is formed by a special oxidation method, a high bonding strength is formed thereon. The metal layer joined by (1) can be formed.

  When forming a fine circuit pattern using an aluminum nitride-based metallized substrate manufactured by such a method, a metal layer having a sufficient area is formed, and unnecessary portions of the metal layer (electrodes and wirings) are formed. In general, a method of removing a portion that does not have to be used is employed. Usually, as a method of removing an unnecessary metal layer, a method of etching an unnecessary portion using a photolithography technique and an ion milling method is employed.

  Also, a method of removing unnecessary metals by ion milling is known as a method for forming fine metal wiring (see Patent Document 2), and a method of laser processing a metallized substrate as a method for manufacturing a highly efficient wiring substrate Is known (see Patent Document 3).

International Publication No. WO2005 / 0753382 Pamphlet JP 2003-209415 A JP 2006-202840 A

  According to Patent Document 1, an aluminum nitride substrate oxidized by a new oxidation method disclosed in the document can be metallized using an alumina metallization method, and the obtained metallization includes a substrate and a metallized layer. It is said that the substrate is hardly deteriorated even if a plating process is applied.

  However, according to the method described in Patent Document 1, the surface of the aluminum nitride substrate is oxidized, and a metallized substrate in which a metal layer is formed on the obtained oxide film is formed by etching unnecessary portions using a photolithographic technique. As a result of forming the pattern, it has been found that insulation between the wirings may not be obtained.

  The ion milling method and the laser processing method are useful methods for forming a fine circuit pattern. However, when these methods are applied to a metallized substrate in which a metal layer is directly formed on an aluminum nitride substrate, the formed wiring It has been found that there may be cases in which insulation cannot be taken.

  Therefore, the present invention is first a metallized substrate using an aluminum nitride substrate having an oxide layer on the surface, and when an unnecessary portion is etched using an ion milling method or a laser processing method to form a fine circuit pattern. It is another object of the present invention to provide a metallized substrate that can ensure insulation between wirings.

  A second object of the present invention is to provide a method for forming a highly reliable fine circuit by applying an ion milling method or a laser processing method to an aluminum nitride metallized substrate.

  The present inventors have examined the cause of the above-described problem in the metallized substrate disclosed in Patent Document 1. As a result, when the oxidation method disclosed in Patent Document 1 is adopted, it is possible to prevent the occurrence of cracks with a wide branch in the oxide film, but the generation of cracks is completely suppressed. It has been found that the metal that has entered the gap between the cracks cannot be removed by ordinary etching, and the wiring is electrically joined by the remaining metal.

  Further, when the cause of the latter problem was examined, when an ion milling method or a laser processing method is applied to a metallized substrate in which a metal layer is directly formed on an aluminum nitride substrate, paragraph 0008 of JP-A-2003-218518 is disclosed. As described in the above, when laser processing is performed, nitrogen atoms of aluminum nitride may be detached and metal Al may be formed, which may be caused by breakdown of insulation. found.

  The present inventors consider that aluminum oxide in which negative atoms are more firmly bonded to aluminum atoms does not form metal Al even when an ion milling method or a laser processing method is applied, and the surface of aluminum nitride In addition, if it is possible to form an oxide film that does not have cracks in which metal enters, the above two problems can be solved at once, and a method for forming such an oxide film was studied.

  As a result, when oxidizing the aluminum nitride substrate, the inside of the furnace in which the aluminum nitride substrate was introduced before the heat treatment was vacuum degassed and heated in an atmosphere introduced with an inert gas, and after reaching the oxidation temperature However, even if the substrate is kept in the same atmosphere, the oxidation of the aluminum nitride substrate proceeds with a trace amount of oxidizing gas contained in the inert gas, and metallization is performed using the substrate thus surface-oxidized. In the case of forming a substrate, the inventors have obtained knowledge that the above-described problems do not occur.

The present invention is a method for producing a metallized ceramic substrate based on such knowledge, and the dew point in the atmosphere from when the temperature is raised to 200 ° C. or higher until the temperature is lowered to less than 1100 ° C. is −50 ° C. And obtaining an aluminum nitride substrate having an aluminum oxide layer on the surface by oxidizing the surface of the aluminum nitride substrate at 1100 to 1700 ° C. for 5 hours or more in an atmosphere having an oxygen partial pressure of 10 ⁻⁴ atm or less, And a step of forming a wiring pattern made of metal on the aluminum oxide layer of the substrate obtained in this step.

  The preceding step in the method for producing a metallized ceramic substrate of the present invention is also a novel method for producing an aluminum nitride substrate having an aluminum oxide layer on the surface, and a surface aluminum oxynitride substrate obtained by the method is also provided. Compared to the surface aluminum oxynitride substrate obtained by the method disclosed in Patent Document 1, the number of voids contained in the oxide layer is large, and the proportion of voids having a large aperture is high. More specifically, among the plurality of voids existing in the aluminum oxide layer, the proportion of the voids having a diameter equivalent to a circle of 0.25 μm or more in the total number of voids is 5% or more and includes the voids. The ratio that the total area of all the voids occupies with respect to the area is 7 to 30%.

That is, according to the second aspect of the present invention, in the method for producing an aluminum nitride substrate having an aluminum oxide layer on the surface thereof by oxidizing the surface of the aluminum nitride substrate, the oxidation is performed at a temperature of 200 ° C. or higher, and then 1100 It is carried out by heating at 1100 to 1700 ° C. for 5 hours or more in an atmosphere where the dew point in the atmosphere until the temperature falls below -50 ° C. is -50 ° C. or lower and the oxygen partial pressure is 10 ⁻⁴ atm or lower. A third feature of the present invention is an aluminum nitride substrate having an aluminum oxide layer on the surface produced by the method.

  According to the method of the present invention, the fine circuit pattern is maintained by maintaining the excellent characteristics of the aluminum nitride-based metallized substrate disclosed in Patent Document 1 and etching an unnecessary portion of the metal layer (metallized layer). Even if formed, an aluminum nitride metallized substrate in which the insulation between the wirings is kept good can be manufactured. Moreover, even if an ion milling method or a laser processing method is applied as a method for removing an unnecessary metal layer, metallization of the underlying ceramic does not occur. Therefore, these methods can be employed to form a finer pattern.

  Although the details of the mechanism for obtaining such an excellent effect are unknown, the surface of the surface aluminum oxynitride substrate obtained by the method of the present invention was analyzed for the oxidized layer. In addition, since the ratio of voids having a large aperture is high, the mechanism is estimated to be as follows. That is, in the method of the present invention, a void having the above-described characteristics is formed in order to oxidize an aluminum nitride substrate very slowly in oxygen at a very low concentration, and stress (formed during oxide film formation or cooling) is formed. The voids absorb or disperse (relax) that occurs due to the difference in the lattice constant between alumina and aluminum nitride), so that the generation of cracks is greatly suppressed, and even if cracks occur, the gaps remain. It is estimated that this is because the metal is not so narrow that the metal does not enter the gap between the cracks. Incidentally, the crack width of the surface of the aluminum nitride substrate having an oxide layer on the surface disclosed in Patent Document 1 does not fall below 100 nm, whereas according to the method of the present invention, the thickness of the oxide film is up to 5 μm. Even when the oxide film thickness is 10 μm, it is about 100 nm.

  The aluminum nitride substrate used in the production method of the present invention may be a single crystalline or polycrystalline crystalline material, amorphous, or a mixture of a crystalline phase and an amorphous layer, and a sintering aid and other materials as necessary. A sintered body obtained by sintering the aluminum nitride substrate powder by adding the above additives can be used. Further, the shape and size thereof are not particularly limited, and a formed body processed into an arbitrary shape such as a plate shape or an irregular shape can be used.

  For example, at least one additive selected from the group consisting of yttria, calcia, calcium nitrate, and barium carbonate is added to aluminum nitride powder, and it is molded into a predetermined shape by a conventional method and then sintered. A thing can be used conveniently.

In the production method of the present invention, the surface of the aluminum nitride substrate is first oxidized in an atmosphere having an oxygen partial pressure of 10 ⁻⁴ atm or less. Since the oxidation start temperature of aluminum nitride is 1100 ° C. as shown in FIG. 1, the oxygen partial pressure in the atmosphere needs to be 10 ⁻⁴ atm or less above the temperature.

The partial pressure of oxygen in the inert gas affects the formation rate of the oxide layer. In general, the higher the oxygen concentration, the faster the formation rate of the oxide layer. However, when the oxygen partial pressure in the atmosphere is higher than 10 ⁻⁴ atm during oxidation, the effect of the present invention cannot be obtained. That is, in the case of forming a wiring pattern made of metal on an aluminum nitride ceramic having an aluminum oxide layer, when a part of the metal film coated in the step is removed by an ion milling method or a laser processing method, There is a problem that nitrogen atoms may be eliminated and metal Al may be formed, thereby breaking the insulation. The oxygen partial pressure of 10 ⁻⁴ atm corresponds to the case where nitrogen gas having an oxygen content of 100 vol ppm is used at atmospheric pressure.

The oxygen partial pressure in the atmosphere during the oxidation is preferably 10 ⁻⁵ atm or less. On the other hand, the oxygen partial pressure is preferably 10 ⁻²⁵ atm or more, and more preferably 10 ⁻¹⁰ atm or more. Oxygen partial pressure when the reaction of the aluminum nitride and aluminum oxide is the oxide has reached equilibrium is extremely small, for example because it is 1300K in 10 ^-25 atm, the oxidation reaction of aluminum nitride in more high oxygen partial pressure Becomes dominant. In general, a commercially available inert gas contains oxygen of about 0.1 to several ppm even if it has a high purity or an ultrahigh purity, and functions sufficiently as an oxidizing gas for aluminum nitride.

  The method for setting the oxygen partial pressure in the above range is not particularly limited, but generally, a commercially available cylinder-containing inert gas having a purity of 99.995% or more such as nitrogen or argon may be used. In order to more precisely control the oxygen partial pressure, a high-purity inert gas of 99.999% or more, more preferably 99.9999% or more, and most preferably 99.99995% or more is used. What is necessary is just to mix oxygen gas so that it may become a desired oxygen partial pressure with such a high purity inert gas.

  Furthermore, if necessary, it is possible to create an extremely low oxygen partial pressure atmosphere by utilizing the chemical equilibrium between carbon monoxide gas, carbon dioxide gas, or a mixed gas of these gases and nitrogen and an aluminum nitride substrate. . However, since commercial products of carbon monoxide gas and carbon dioxide gas contain a relatively large amount of oxygen gas as an impurity, if the oxygen partial pressure is too high, the gas will not reach the object to be processed using an oxygen scavenger. It is necessary to remove enough oxygen. As the oxygen scavenger, a highly active reducing agent such as graphite or titanium sponge can be used. Moreover, you may control the oxygen partial pressure in a furnace using a vacuum pump.

  The oxidation temperature is not particularly limited as long as it is 1100 ° C. or higher. However, in order to appropriately control the thickness of the oxide layer, it is preferable to set the temperature to 600 ° C. or lower (that is, 1100 to 1700 ° C.) higher than the oxidation start temperature. is there. Preferably it is 1150-1500 degreeC, Especially 1200-1400 degreeC.

  In the present invention, the oxidation time must be 5 hours or more. In the production method of the present invention, since the oxygen partial pressure is low, the oxidation rate is slower than oxidation in air. Therefore, the required oxide film thickness cannot be obtained by short-time oxidation. Although it can determine suitably according to oxidation temperature and the thickness (it mentions later) of the oxidation layer to obtain, suitable oxidation time is 10 to 500 hours, More preferably, it is 30 to 200 hours.

Conditions such as the atmosphere until the temperature is raised to the oxidation temperature and the rate of temperature rise are not particularly limited, but in order to obtain a better quality oxide layer, the temperature is preferably higher than 1000 ° C., more preferably At a temperature higher than 800 ° C., the oxygen partial pressure in the atmosphere is set to 10 ⁻⁴ atm (more preferably 10 ⁻⁵ atm) or less.

  Furthermore, it is preferable to keep the oxygen partial pressure low until the temperature reaches 800 ° C. after the temperature of the aluminum nitride substrate reaches 200 ° C. or higher, more preferably 100 ° C. or higher. This is because when the atmosphere at the time of temperature rise is an atmosphere having a high oxygen partial pressure such as air, oxygen is dissolved in the aluminum nitride substrate to be treated at the time of temperature rise and heating, and the width is relatively wide during the oxidation reaction. This is because there is a high possibility that a lot of cracks with many branches will occur.

The oxygen partial pressure in the range of 100 ° C. (or 200 ° C.) to 800 ° C. is preferably 10 ⁻² atm or less, more preferably 10 ⁻⁴ atm or less, and preferably 10 ⁻⁵ atm or less. Particularly preferred.

Further, from the viewpoint of easy atmosphere control, the oxygen partial pressure in the furnace is set to 10 before reaching 200 ° C. (preferably 100 ° C.) after introducing the aluminum nitride substrate to be processed into the furnace for oxidation. ^It is preferable that the oxygen partial pressure is ⁻⁴ atm or less, more preferably 10 ⁻⁵ atm or less, and then the oxygen partial pressure is maintained until the temperature falls below the oxidation temperature (1100 ° C.) in the temperature lowering step.

Note In the production method of the present invention, during the oxidation, i.e., it is preferable to always oxygen partial pressure is under the range while the substrate temperature is in the 1100 ° C. or more, temporarily 10 ^-4 atm or more and It may be. Of the time when the substrate temperature is 1100 ° C. or more, 80% or more is preferably within the above range, more preferably 90% or more, further preferably 95% or more, and 100%. Most preferably it is.

  In addition, since water (water vapor) is greatly involved in oxidation, the production method of the present invention has a dew point of −200 ° C. or higher (preferably 100 ° C. or higher) until the temperature drops below 1100 ° C. It is desirable to carry out in an atmosphere controlled at 50 ° C. or lower, preferably −60 ° C. or lower, more preferably −65 ° C. or lower, particularly −70 ° C. or lower.

The atmosphere control at a temperature lower than the oxidation temperature can be performed in the same manner as the atmosphere control at the oxidation temperature. In addition, in order to reliably remove the initial oxygen in the furnace where the oxidation is performed and to reduce the oxygen partial pressure during the oxidation to 10 ⁻⁴ atm or less, the aluminum nitride substrate is introduced into the furnace, and then the inside of the furnace is evacuated. It is desirable to replace it with an inert gas as described above. The vacuum degassing and inert gas replacement are more preferably performed a plurality of times. The degree of pressure reduction during vacuum degassing is not particularly limited, but the pressure in the furnace is preferably 100 Pa or less, particularly 20 Pa or less, and most preferably 1 Pa or less.

  The temperature increasing / decreasing rate at the time of oxidation is not particularly limited, and the temperature may be increased within a practically controllable temperature rising rate range, for example, 10 to 80 ° C./min, preferably 30 to 50 ° C./min. Note that if the temperature rising rate is set to an extremely high rate, for example, 80 ° C./min or more, the proportion of oxygen dissolved in the aluminum nitride substrate is low. The need for control can be reduced.

  On the other hand, when the temperature is lowered, cooling is performed at a rate of 3 ° C./min or less, preferably 1 ° C./min or less, more preferably 0.5 ° C./min or less so as not to give a thermal shock to the oxidized aluminum nitride substrate as much as possible. It is good to do.

  The surface-oxidized aluminum nitride substrate thus obtained has an aluminum oxide (alumina) layer as an oxide layer on the surface. The thickness of the oxide layer is preferably 3 μm or more from the viewpoint of preventing aluminum nitride from becoming a conductor when forming a wiring pattern by an ion milling method or a laser processing method. On the other hand, if the thickness of the oxide layer is too thick, cracks that are relatively wide and have many branches that are presumed to be derived from the difference in thermal expansion coefficient between aluminum nitride and aluminum oxide are likely to occur, resulting in a decrease in adhesion. There is a case. For this reason, the thickness of the aluminum oxide layer formed by the production method of the present invention is preferably 15 μm or less, and more preferably 10 μm or less. The thickness of the oxide layer to be formed depends on the oxidation conditions, and becomes thicker as it is oxidized at a higher temperature or for a longer time.

  Further, according to the study by the present inventors, it has been clarified that the oxide layer formed by the method as described above has a specific structure having voids. That is, when the measurement / analysis is performed by the method described in Examples described later, the ratio of the void portion in the oxide layer is 7 to 30%, and the void equivalent to the circle equivalent diameter in the void is 0.25 μm or more. It has a feature that it is present in an area of 5% or more.

  Considering the adhesion of the oxide layer, the ratio of the area occupied by the voids in the oxide layer is 7 to 20%, and the voids with an equivalent circle diameter of 0.25 μm or more are 5 to 25% of the total number of voids. preferable. Furthermore, it is preferable that the voids having an equivalent circle diameter of 0.3 μm or more are 2% or more of the total number of voids.

  An electronic circuit substrate made of an aluminum nitride substrate having an oxide layer with a thickness of 0.1 to 10 μm oxidized by a conventional method has high adhesion strength of the metal layer when the metal layer is formed on the surface thereof. However, usually, the adhesion strength starts to decrease when the thickness of the oxide layer exceeds 3 μm, and when the thickness exceeds 5 μm, the strength decreases to about half of the initial strength. However, the aluminum nitride substrate having an oxide layer obtained by the above-described production method of the present invention maintains practically sufficient adhesion strength even when the thickness of the oxide layer is 3 μm or more. The adhesion strength does not decrease.

  Therefore, if the metal wiring pattern is formed on the surface-oxidized aluminum nitride substrate manufactured by the above method, the adhesion between the substrate and the metallized layer is high, the durability against heat cycle is high, and the plating process is further performed. However, it is possible to manufacture a metallized ceramic substrate in which the substrate is not easily deteriorated, and even if a fine circuit pattern is formed, it is easy to maintain good insulation between wires (good yield).

  As a method of forming a metal wiring pattern on a surface-oxidized aluminum nitride substrate, a known method may be employed as appropriate. For example, the entire surface of the substrate is coated with a metal film, and a part of the coated metal film is formed. A step of removing by an ion milling method or a laser processing method can be suitably employed.

  The metal used for coating may be appropriately selected as desired, and can be coated with copper, aluminum, gold, silver, platinum, titanium, tungsten, nickel, molybdenum, palladium, or an alloy thereof.

  The method of coating with a metal film is not particularly limited, and a known method can be adopted, for example, a thick film method, a post-fire method, electroplating, electroless plating, vapor deposition, sputtering, ion plating, CVD method, Metal coating is possible by direct bonding of metal plates.

  For example, a circuit board coated with nickel and gold after screen printing and baking of copper conductor paste is used as a power module substrate or a submount for mounting semiconductor elements.

  The metal coating thickness is not particularly limited, and is usually about 0.1 to 100 μm.

  In order to form a desired wiring pattern on the metal coating formed on the entire surface of the substrate, for example, a resist is applied on the substrate on which the metal layer has been formed by sputtering, development is performed after exposure with a predetermined pattern, and an argon ion beam is formed. The metal in the exposed portion may be removed by irradiation (ion milling), or the metal layer may be removed (laser processing) by irradiating the metal layer with a specific wavelength laser such as a YAG laser or excimer laser.

  The metallized ceramic substrate manufactured as described above is excellent in various performances such as adhesion of metal wiring patterns, and it is easy to maintain good insulation between wirings even if a fine circuit pattern is formed. It is an excellent metallized ceramic substrate.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

Example 1
An aluminum nitride substrate (SH30 manufactured by Tokuyama Corporation) having a plate shape of 50.8 mm in length, 50.8 mm in width, and 0.635 mm in thickness and having a surface roughness Ra of 0.2 μm or less has an inner diameter of 120 mm and a length of 1000 mm. After introducing into a high-temperature atmosphere furnace (small high-temperature atmosphere furnace manufactured by Tokai High Heat Industry Co., Ltd.) using mullite ceramics as the furnace tube, the inside of the furnace was depressurized to 0.1 Pa or less with a rotary vacuum pump, and then nitrogen gas (purity 99.99). The pressure was replaced to atmospheric pressure at 99998%, dew point −80 ° C., oxygen content 0.3 vol ppm), and the temperature was raised to 1350 ° C. under a nitrogen flow rate of 0.5 (l / min) (heating rate: 3.3 ° C./min). After the temperature in the vicinity of the substrate reached 1350 ° C., the surface of the aluminum nitride substrate was oxidized as it was for 75 hours (oxygen partial pressure: 10 ⁻⁷ atm). Even after completion of the holding, the atmosphere was maintained as it was, and cooled to room temperature at a cooling rate of 3 ° C./min to obtain the surface aluminum oxynitride material of the present invention.

  The obtained surface aluminum oxynitride material (sample) was analyzed using X-ray diffraction (XRD) and a scanning electron microscope (SEM). Details of the various analyzes are shown below.

[Identification of reaction product by XRD]
When XRD measurement was performed on the sample using an X-ray diffractometer (X-ray diffractometer RINT1200 manufactured by Rigaku Corporation), the diffraction pattern confirmed that the oxide layer of the sample was α-alumina. . The measurement was performed with incident X-ray Cu—Kα ray, tube voltage 40 kV, tube current 40 mA, light receiving slit 0.15 mm, and monochrome light receiving slit 0.60 mm.

[SEM and surface observation by SEM]
The sample was cut into 5 mm × 5 mm with a diamond cutter, and then fixed on the observation sample stage with carbon tape with the oxidized surface facing up. This was coated with Pt using an ion sputtering apparatus (magnetron sputtering apparatus JUC-5000 manufactured by JEOL Ltd.), and the surface of the sample was observed with an FE-SEM (field emission scanning electron microscope JSM-6400 manufactured by JEOL Ltd.). Went. Observation was carried out at an acceleration voltage of 15 kV, a probe current of 5 × 10 ⁻¹¹ A, an emission current of 8 μA, and a magnification of 10,000 times, and an arbitrary field of view was observed, and the same part was photographed. A typical photograph is shown in FIG. 2, and its illustration is shown in FIG. As shown in FIG. 3, aluminum oxide crystals grew on the surface of the oxide layer in a state reflecting the surface state of the base, and some elongated cracks were observed. From FIG. 3, the length of the line connecting the crack grooves in the shortest length was measured, and the average of 30 points was obtained using this as the crack width. . Moreover, when the thickness of the oxide layer was calculated | required by SEM observation of the torn surface of a sample, the thickness was 3.4 micrometers on average. An arbitrary field of view was observed at 10 locations, and the same locations were photographed. A typical photograph of the cross section is shown in FIG. 4, and an illustration thereof is shown in FIG. Innumerable voids having various shapes as shown in FIGS. 5 and 6 were observed in the oxide layer. When image analysis was performed on these cross-sectional photographs, the ratio of the total void area to the oxide layer was 10.1%. Further, the ratio of the number of voids having a circle equivalent diameter of 0.2 μm, 0.25 μm, and 0.3 μm to the entire voids was 11%, 5%, and 2%, respectively.

[Void analysis of oxide layer cross section by image analysis software]
Data obtained by tracing the cross-sectional shape of the oxide layer by SEM observation was analyzed using image analysis software IP-1000 (integrated application: A image-kun) manufactured by Asahi Kasei Kogyo. First, particle analysis was performed on the outline of the oxide layer including voids, and the total area of the oxide layer was determined. Next, particle analysis was similarly performed on the outline of the voids in the oxide layer, and distribution data according to the total area of the voids and the equivalent circle diameters of the voids were obtained. Further, the ratio of the voids having an equivalent circle diameter φ of 0.3 μm, 0.25 μm, and 0.2 μm to the total number of voids and the ratio of the total area of all voids to the area of the oxide layer including the voids were obtained.

[Preparation for void analysis of oxide layer cross section by image analysis software]
Two photographs of the fracture surface of the sample taken by SEM were copied at 200 times (equal magnification = 100 times), and tracing paper was placed on top and fixed. One sheet traces the outline of the oxide layer containing voids with an ultra-fine magic pen, and the other sheet traces the outline of the voids present in the oxide layer and reads them with a scanner and stores them electronically in a bitmap format. . The same work was done on a photograph taken from another field of view.

  Thin film metallization (Ti / Pt / Au = 0.06 / 0.2 / 0.6 μm) was applied on the surface aluminum oxynitride material by sputtering. A 42 alloy nail head pin with a head diameter of 1.1 mm and Ni plated on the metallized layer was joined with a flux and a Pb-Sn eutectic solder chip, and the peel test was performed by pulling the pin vertically at a speed of 10 mm per minute. . The tensile strength when the pin was peeled from the material was taken as the peel strength and measured at 10 points. The average peel strength was a high strength of 90 MPa. The peeling mode was 9 aluminum nitride internal fractures and 1 inter-solder fracture among 10 measured locations. Table 1 shows the peel strength and the fracture mode at each measurement point.

  Furthermore, when the circuit was formed by photolithography and ion milling so that the width between the circuits was 100 μm, and the electrical resistance between the circuits was measured with a digital multimeter R6871 manufactured by Advantest Co., Ltd., the measurement was above the upper limit of measurement (at least 100 MΩ). It was.

Example 2
An aluminum nitride substrate (SH30 manufactured by Tokuyama Corporation) having a plate shape of 50.8 mm in length, 50.8 mm in width, and 0.635 mm in thickness and having a surface roughness Ra of 0.2 μm or less is used in the same apparatus as in Example 1. After introducing and reducing the pressure in the furnace to 0.1 Pa or less with a rotary vacuum pump, the pressure was returned to atmospheric pressure with nitrogen gas (purity 99.99%, dew point -65 ° C., oxygen content 50 vol ppm), The temperature was raised to 1300 ° C. under a nitrogen flow of 0.5 (l / min) (heating rate: 3.3 ° C./min). After the temperature in the vicinity of the substrate reached 1300 ° C., the surface of the aluminum nitride substrate was oxidized as it was kept for 100 hours (oxygen partial pressure: 10 ⁻⁵ atm). Even after completion of the holding, the atmosphere was maintained as it was, and cooled to room temperature at a cooling rate of 3 ° C./min to obtain the surface aluminum oxynitride material of the present invention.

  About the obtained surface aluminum oxynitride material (sample), the identification of the oxide layer by X-ray diffraction (XRD) and the observation of the surface and fractured surface by a scanning electron microscope (SEM) were performed as in Example 1. From the XRD diffraction pattern, it was confirmed that the oxidized layer of the sample was α-alumina. Next, FIG. 6 (photograph) and FIG. 7 (illustration of FIG. 6) show the surface observation result by SEM, and FIG. 8 (photograph) and FIG. 9 (illustration of FIG. 8) show the cross-sectional observation result. As shown in FIG. 6, aluminum oxide crystals grew on the surface of the oxide layer in a state reflecting the surface state of the base, and some elongated cracks were observed. From the surface observation photograph of FIG. 6 and other 4 fields, the total average of the crack widths of all 5 fields was determined to be 56 nm. Moreover, when the thickness of the oxide layer was calculated | required by SEM observation of the torn surface of a sample, the thickness was 5.4 micrometers on average. Innumerable voids having various shapes as shown in FIGS. 8 and 9 were observed in the oxide layer. When image analysis was performed on these cross-sectional photographs, the ratio of the total void area to the oxide layer was 13.7%. In addition, the ratio of the number of voids having an equivalent circle diameter of 0.2 μm, 0.25 μm, and 0.3 μm to the entire voids in the voids was 22%, 12%, and 8%, respectively.

When a thin film metallization was applied to the above surface aluminum oxynitride substrate in the same manner as in Example 1 and a peel test was conducted, the average peel strength at 10 points was as high as 77 MPa. The peeling mode was 9 aluminum nitride internal fractures and 1 inter-solder fracture among 10 measured locations. Table 1 shows the peel strength and the fracture mode at each measurement point.
Furthermore, when a circuit was formed in the same manner as in Example 1 and the electrical resistance between the circuits was measured, it was equal to or greater than the measurement upper limit.

Example 3
An aluminum nitride substrate (SH30 manufactured by Tokuyama Corporation) having a plate shape of 50.8 mm in length, 50.8 mm in width, and 0.635 mm in thickness and having a surface roughness Ra of 0.2 μm or less is used in the same apparatus as in Example 1. After introducing and reducing the pressure in the furnace to 0.1 Pa or less with a rotary vacuum pump, the pressure was replaced with nitrogen gas (purity 99.99999%, dew point -80 ° C, oxygen content 0.3 vol ppm) to atmospheric pressure. The temperature was raised to 1350 ° C. under a nitrogen flow with a flow rate of 0.5 (l / min) (temperature increase rate: 3.3 ° C./min). After the temperature near the substrate reached 1350 ° C., the surface of the aluminum nitride substrate was oxidized as it was for 100 hours (oxygen partial pressure: 10 ⁻⁷ atm). Even after completion of the holding, the atmosphere was maintained as it was, and cooled to room temperature at a cooling rate of 3 ° C./min to obtain the surface aluminum oxynitride material of the present invention.

  About the obtained surface aluminum oxynitride material (sample), the identification of the oxide layer by X-ray diffraction (XRD) and the observation of the surface and fractured surface by a scanning electron microscope (SEM) were performed as in Example 1. From the XRD diffraction pattern, it was confirmed that the oxidized layer of the sample was α-alumina. Next, the surface observation result by SEM is shown in FIG. 10 (photograph) and FIG. 11 (illustration of FIG. 10), and the cross-sectional observation result is shown in FIG. 12 (photograph) and FIG. 13 (illustration of FIG. 12). As shown in FIG. 10, aluminum oxide crystals grew on the surface of the oxide layer in a state reflecting the surface state of the base, and some elongated cracks were observed. From the surface observation photograph of FIG. 10 and the other 4 fields, the total average of the crack widths of all 5 fields was determined to be 95 nm. Moreover, when the thickness of the oxide layer was calculated | required by SEM observation of the torn surface of a sample, the thickness was 8.7 micrometers on average. Innumerable voids having various shapes as shown in FIGS. 12 and 13 were observed in the oxide layer. When image analysis was performed on these cross-sectional photographs, the ratio of the total void area to the oxide layer was 15.3%. In addition, the ratio of the number of voids having an equivalent circle diameter of 0.2 μm, 0.25 μm, and 0.3 μm to the entire voids in the voids was 25%, 13%, and 7%, respectively.

  When a thin film metallization was performed on the surface aluminum oxynitride material in the same manner as in Example 1 and a peel test was performed, the average peel strength at 10 points was 64 MPa. The peeling mode was 9 aluminum nitride internal fractures and 1 inter-solder fracture among 10 measured locations. Table 1 shows the peel strength and the fracture mode at each measurement point.

  Further, when a circuit was formed in the same manner as in Example 1 and the electrical resistance between the circuits was measured, it was equal to or greater than the measurement upper limit value.

Example 4
An aluminum nitride substrate (SH30 manufactured by Tokuyama Corporation) having a plate shape of 50.8 mm in length, 50.8 mm in width, and 0.4 mm in thickness and having a surface roughness Ra of 0.05 μm or less is used in the same apparatus as in Example 1. After introducing and depressurizing the inside of the furnace to 0.1 Pa or less with a rotary vacuum pump, the pressure was replaced with nitrogen gas (purity 99.99%, dew point -60 ° C, oxygen content 50 vol ppm) to atmospheric pressure, The temperature was raised to 1350 ° C. under a nitrogen flow of 0.5 (l / min) (heating rate: 3.3 ° C./min). After the temperature in the vicinity of the substrate reached 1300 ° C., the surface of the aluminum nitride substrate was oxidized as it was kept for 80 hours (oxygen partial pressure: 10 ⁻⁵ atm). Even after completion of the holding, the atmosphere was maintained as it was, and cooled to room temperature at a cooling rate of 3 ° C./min to obtain the surface aluminum oxynitride material of the present invention.

  About the obtained surface aluminum oxynitride material (sample), the identification of the oxide layer by X-ray diffraction (XRD) and the observation of the surface and fractured surface by a scanning electron microscope (SEM) were performed as in Example 1. From the XRD diffraction pattern, it was confirmed that the oxidized layer of the sample was α-alumina. From the surface SEM photograph of the surface of the oxide layer, the total average width of cracks in all five fields was determined to be 89 nm. Moreover, when the thickness of the oxide layer was calculated | required by SEM observation of the torn surface of a sample, the thickness was 6.2 micrometers on average.

  When a thin film metallization was performed on the surface aluminum oxynitride material in the same manner as in Example 1 and a peel test was performed, the average peel strength at 10 points was 93 MPa. In addition, the peeling mode was 2 aluminum nitride internal fractures and 8 inter-solder fractures among 10 measured locations. Table 1 shows the peel strength and the fracture mode at each measurement point.

  Further, when a circuit was formed in the same manner as in Example 1 and the electrical resistance between the circuits was measured, it was equal to or greater than the measurement upper limit value.

Example 5
An aluminum nitride substrate (SH30 manufactured by Tokuyama Corporation) having a plate shape of 50 mm in length, 25 mm in width, and 0.8 mm in thickness and having a surface roughness Ra of 0.5 μm or less was introduced into the same apparatus as in Example 1, After reducing the pressure to 0.1 Pa or less with a rotary vacuum pump, the pressure was reduced to atmospheric pressure with nitrogen gas (purity 99.99999%, dew point -80 ° C., oxygen content 0.3 vol ppm), and the flow rate was set to 0. The temperature was raised to 1250 ° C. under a nitrogen flow of 5 (l / min) (heating rate: 3.3 ° C./min). After the temperature in the vicinity of the substrate reached 1250 ° C., the surface of the aluminum nitride substrate was oxidized by maintaining it for 100 hours (oxygen partial pressure: 10 ⁻⁷ atm). Even after completion of the holding, the atmosphere was maintained as it was, and cooled to room temperature at a cooling rate of 3 ° C./min to obtain the surface aluminum oxynitride material of the present invention.

  About the obtained surface aluminum oxynitride material (sample), the identification of the oxide layer by X-ray diffraction (XRD) and the observation of the surface and fractured surface by a scanning electron microscope (SEM) were performed as in Example 1. From the XRD diffraction pattern, it was confirmed that the oxidized layer of the sample was α-alumina. It was 29 nm when the total average of the width | variety of the crack of all the 5 visual fields was calculated | required from the surface SEM photograph of the oxide layer surface. Moreover, when the thickness of the oxide layer was calculated | required by SEM observation of the torn surface of a sample, the thickness was 3.2 micrometers on average. When a thin film metallization was applied to the surface aluminum oxynitride material in the same manner as in Example 1 and a peel test was conducted, the average peel strength at 10 points was 86 MPa. The peeling mode was 8 aluminum nitride internal fractures and 2 inter-solder fractures among 10 measured locations. Table 1 shows the peel strength and the fracture mode at each measurement point.

  Further, when a circuit was formed in the same manner as in Example 1 and the electrical resistance between the circuits was measured, it was equal to or greater than the measurement upper limit value.

Example 6
An aluminum nitride substrate (SH30 manufactured by Tokuyama Corporation) having a plate shape of 50 mm in length, 25 mm in width, and 0.8 mm in thickness and having a surface roughness Ra of 0.5 μm or less was introduced into the same apparatus as in Example 1, After reducing the pressure to 0.1 Pa or less with a rotary vacuum pump, the pressure was reduced to atmospheric pressure with nitrogen gas (purity 99.99999%, dew point -80 ° C., oxygen content 0.3 vol ppm), and the flow rate was set to 0. The temperature was raised to 1385 ° C. under a nitrogen flow of 5 (l / min) (heating rate: 3.3 ° C./min). After the temperature near the substrate reached 1385 ° C., the surface of the aluminum nitride substrate was oxidized as it was for 100 hours (oxygen partial pressure: 10 ⁻⁷ atm). Even after completion of the holding, the atmosphere was maintained as it was, and cooled to room temperature at a cooling rate of 3 ° C./min to obtain the surface aluminum oxynitride material of the present invention.

  About the obtained surface aluminum oxynitride material (sample), the identification of the oxide layer by X-ray diffraction (XRD) and the observation of the surface and fractured surface by a scanning electron microscope (SEM) were performed as in Example 1. From the XRD diffraction pattern, it was confirmed that the oxidized layer of the sample was α-alumina. From the surface SEM photograph of the surface of the oxide layer, the total average width of cracks in all five fields was determined to be 42 nm. Moreover, when the thickness of the oxide layer was calculated | required by SEM observation of the torn surface of a sample, the thickness was 10.0 micrometers on average. When a thin film metallization was applied to the surface aluminum oxynitride material in the same manner as in Example 1 and a peel test was conducted, the average peel strength at 10 points was 95 MPa. The peeling mode was all inter-solder fracture. Table 2 shows the peel strength and fracture mode at each measurement point.

  Further, when a circuit was formed in the same manner as in Example 1 and the electrical resistance between the circuits was measured, it was equal to or greater than the measurement upper limit value.

Comparative Example 1
An aluminum nitride substrate (SH30 manufactured by Tokuyama Corporation) having a plate shape of 50.8 mm in length, 50.8 mm in width, and 0.635 mm in thickness and having a surface roughness Ra of 0.05 μm or less is used in the same apparatus as in Example 1. After introducing and reducing the pressure in the furnace to 0.1 Pa or less with a rotary vacuum pump, the pressure was replaced with nitrogen gas (purity 99.99999%, dew point -80 ° C, oxygen content 0.3 vol ppm) to atmospheric pressure. The temperature was raised to 1200 ° C. under a nitrogen flow with a flow rate of 0.5 (l / min) (temperature increase rate: 3.3 ° C./min). After the temperature near the substrate reaches 1200 ° C., the flow of nitrogen gas is stopped, and then dry-air (dew point −80 ° C.) dried with a dryer is allowed to flow at a flow rate of 0.5 (l / min). The surface of the aluminum nitride substrate was oxidized for 30 hours as it was (oxygen partial pressure: 0.21 atm). Even after completion of the holding, the atmosphere was maintained as it was, and cooled to room temperature at a cooling rate of 3 ° C./min to obtain the surface aluminum oxynitride material of the present invention.

  About the obtained surface aluminum oxynitride material (sample), the identification of the oxide layer by X-ray diffraction (XRD) and the observation of the surface and fractured surface by a scanning electron microscope (SEM) were performed as in Example 1. From the XRD diffraction pattern, it was confirmed that the oxidized layer of the sample was α-alumina. Next, FIG. 14 (photograph) and FIG. 15 (illustration of FIG. 14) show the surface observation results by SEM, and FIG. 16 (photograph) and FIG. 17 (illustration of FIG. 16) show the cross-sectional observation results. As shown in FIG. 14, streaky patterns due to bulges were observed on the surface of the oxide layer, and some elongated cracks were observed. From the surface observation photograph of FIG. 14 and the other 4 fields, the total average of the crack widths of all 5 fields was found to be 104 nm. Moreover, when the thickness of the oxide layer was calculated | required by SEM observation of the torn surface of a sample, the thickness was 6.1 micrometers on average. In the oxide layer, voids having various shapes as shown in FIGS. 16 and 17 were observed, but the diameter was smaller than that of Example 2 which had the same thickness of the oxide layer. There were few. There was little especially in the vicinity of the surface. When image analysis was performed on these cross-sectional photographs, the ratio of the total void area to the oxide layer was 3.4%. Further, the ratio of the number of voids having a circle equivalent diameter of 0.2 μm, 0.25 μm, and 0.3 μm to the entire voids was 6%, 3%, and 1%, respectively.

  When a thin film metallization was applied to the above surface aluminum oxynitride material in the same manner as in Example 1 and a peel test was conducted, the average peel strength at 10 points was a high strength of 41 MPa. Moreover, all peeling modes were destruction between an oxide layer and aluminum nitride. Table 2 shows the peel strength and fracture mode at each measurement point.

  Furthermore, when a circuit was formed in the same manner as in Example 1 and the electrical resistance between the circuits was measured, it was 13.4Ω.

Comparative Example 2
An aluminum nitride substrate (SH30 manufactured by Tokuyama Corporation) having a plate shape of 50.8 mm in length, 50.8 mm in width, and 0.635 mm in thickness and having a surface roughness Ra of 0.05 μm or less is used in the same apparatus as in Example 1. After introducing and reducing the pressure in the furnace to 0.1 Pa or less with a rotary vacuum pump, the pressure was replaced with nitrogen gas (purity 99.99999%, dew point -80 ° C, oxygen content 0.3 vol ppm) to atmospheric pressure. The temperature was raised to 1300 ° C. under a flow of nitrogen at a flow rate of 0.5 (l / min) (heating rate: 3.3 ° C./min). After the temperature near the substrate reaches 1300 ° C., the flow of nitrogen gas is stopped, and then dry-air (dew point −80 ° C.) dried with a dryer is flowed at a flow rate of 0.5 (l / min), The surface of the aluminum nitride substrate was oxidized for 15 hours as it was (oxygen partial pressure: 0.21 atm). Even after completion of the holding, the atmosphere was maintained as it was, and cooled to room temperature at a cooling rate of 3 ° C./min to obtain the surface aluminum oxynitride material of the present invention.

  About the obtained surface aluminum oxynitride material (sample), the identification of the oxide layer by X-ray diffraction (XRD) and the observation of the surface and fractured surface by a scanning electron microscope (SEM) were performed as in Example 1. From the XRD diffraction pattern, it was confirmed that the oxidized layer of the sample was α-alumina. Next, FIG. 18 (photograph) and FIG. 19 (illustration of FIG. 18) show the surface observation result by SEM, and FIG. 20 (photograph) and FIG. 21 (illustration of FIG. 20) show the cross-sectional observation result. As shown in FIG. 18, streaky patterns due to bulges were observed on the surface of the oxide layer, and some elongated cracks were observed. From the surface observation photograph of FIG. 18 and the other four fields, the total average of the crack widths of all the five fields was determined and found to be 175 nm. Moreover, when the thickness of the oxide layer was calculated | required by SEM observation of the torn surface of a sample, the thickness was 8.3 micrometers on average. In the oxide layer, voids having various shapes as shown in FIGS. 20 and 21 were observed, but the diameter was smaller than that of Example 3 which was the same thickness of the oxide layer. There were few. There was little especially in the vicinity of the surface. When image analysis was performed on these cross-sectional photographs, the ratio of the total void area to the oxide layer was 3.7%. Further, the ratio of the number of voids having an equivalent circle diameter of 0.2 μm, 0.25 μm, and 0.3 μm to the entire voids was 13%, 5%, and 3%, respectively.

  When a thin film metallization was applied to the above surface aluminum oxynitride substrate in the same manner as in Example 1 and a peel test was conducted, the average peel strength at 10 points was 43 MPa. Moreover, all peeling modes were destruction between an oxide layer and aluminum nitride. Table 2 shows the peel strength and fracture mode at each measurement point.

  Furthermore, when a circuit was formed in the same manner as in Example 1 and the electrical resistance between the circuits was measured, it was 0.6Ω.

Comparative Example 3
An aluminum nitride substrate (SH30 manufactured by Tokuyama Corporation) having a plate shape of 50.8 mm in length, 50.8 mm in width, and 0.635 mm in thickness and having a surface roughness Ra of 0.05 μm or less is used in the same apparatus as in Example 1. After introducing and reducing the pressure in the furnace to 0.1 Pa or less with a rotary vacuum pump, the pressure was replaced with nitrogen gas (purity 99.99999%, dew point -80 ° C, oxygen content 0.3 vol ppm) to atmospheric pressure. The temperature was raised to 1300 ° C. under a flow of nitrogen at a flow rate of 0.5 (l / min) (heating rate: 3.3 ° C./min). After the temperature near the substrate reaches 1300 ° C., the flow of nitrogen gas is stopped, and then dry-air (dew point −80 ° C.) dried with a dryer is flowed at a flow rate of 0.5 (l / min), The surface of the aluminum nitride substrate was oxidized as it was for 50 hours (oxygen partial pressure: 0.21 atm). Even after completion of the holding, the atmosphere was maintained as it was, and cooled to room temperature at a cooling rate of 3 ° C./min to obtain the surface aluminum oxynitride material of the present invention.

  About the obtained surface aluminum oxynitride material (sample), the identification of the oxide layer by X-ray diffraction (XRD) and the observation of the surface and fractured surface by a scanning electron microscope (SEM) were performed as in Example 1. From the XRD diffraction pattern, it was confirmed that the oxidized layer of the sample was α-alumina. From the surface SEM photograph of the surface of the oxide layer, the total average width of cracks in all five fields was determined to be 150 nm. Moreover, when the thickness of the oxide layer was calculated | required by SEM observation of the torn surface of a sample, the thickness was 7.3 micrometers on average. When a thin film metallization was applied to the surface aluminum oxynitride material in the same manner as in Example 1 and a peel test was performed, the average peel strength at 10 points was 51 MPa. Moreover, all peeling modes were destruction between an oxide layer and aluminum nitride. Table 2 shows the peel strength and fracture mode at each measurement point.

  Furthermore, when a circuit was formed in the same manner as in Example 1 and the electrical resistance between the circuits was measured, it was 1.9 kΩ.

Comparative Example 4
An aluminum nitride substrate (SH30 manufactured by Tokuyama Corporation) having a plate shape of 50.8 mm in length, 50.8 mm in width, and 0.635 mm in thickness and having a surface roughness Ra of 0.05 μm or less is used in the same apparatus as in Example 1. After introducing and reducing the pressure in the furnace to 0.1 Pa or less with a rotary vacuum pump, the pressure was replaced with nitrogen gas (purity 99.99999%, dew point -80 ° C, oxygen content 0.3 vol ppm) to atmospheric pressure. The temperature was raised to 1300 ° C. under a flow of nitrogen at a flow rate of 0.5 (l / min) (heating rate: 3.3 ° C./min). After the temperature near the substrate reaches 1300 ° C., the flow of nitrogen gas is stopped, and then dry-air (dew point −80 ° C.) dried with a dryer is flowed at a flow rate of 0.5 (l / min), The surface of the aluminum nitride substrate was oxidized for 30 hours as it was (oxygen partial pressure: 0.21 atm). Even after completion of the holding, the atmosphere was maintained as it was, and cooled to room temperature at a cooling rate of 3 ° C./min to obtain the surface aluminum oxynitride material of the present invention.

  About the obtained surface aluminum oxynitride material (sample), the identification of the oxide layer by X-ray diffraction (XRD) and the observation of the surface and fractured surface by a scanning electron microscope (SEM) were performed as in Example 1. From the XRD diffraction pattern, it was confirmed that the oxidized layer of the sample was α-alumina. From the surface SEM photograph of the surface of the oxide layer, the total average width of cracks in all five fields was determined to be 100 nm. Moreover, when the thickness of the oxide layer was calculated | required by SEM observation of the torn surface of a sample, the thickness was 5.4 micrometers on average. When a thin film metallization was applied to the surface aluminum oxynitride material in the same manner as in Example 1 and a peel test was conducted, the average peel strength at 10 points was 47 MPa. Moreover, all peeling modes were destruction between an oxide layer and aluminum nitride. Table 2 shows the peel strength and fracture mode at each measurement point.

  Furthermore, when a circuit was formed in the same manner as in Example 1 and the electrical resistance between the circuits was measured, it was 32.1Ω.

This figure is a graph showing a reaction rate and a change pattern of DTA when an aluminum nitride substrate is heated in an oxygen gas atmosphere. This figure is a SEM photograph of the surface of the oxide layer of the aluminum nitride substrate having the oxide layer on the surface obtained in the oxidation step of Example 1. This figure is a sketch of the SEM photograph of FIG. This figure is a SEM photograph of a fracture surface of an aluminum nitride substrate having an oxide layer on the surface obtained in the oxidation step of Example 1. This figure is a sketch of the SEM photograph of FIG. This figure is an SEM photograph of the surface of the oxide layer of the aluminum nitride substrate having the oxide layer on the surface obtained in the oxidation step of Example 2. This figure is a sketch of the SEM photograph of FIG. This figure is a SEM photograph of a fracture surface of an aluminum nitride substrate having an oxide layer on the surface obtained in the oxidation step of Example 2. This figure is a sketch of the SEM photograph of FIG. This figure is a SEM photograph of the surface of the oxide layer of the aluminum nitride substrate having the oxide layer on the surface obtained in the oxidation step of Example 3. This figure is a sketch of the SEM photograph of FIG. This figure is a SEM photograph of a fracture surface of an aluminum nitride substrate having an oxide layer on the surface obtained in the oxidation step of Example 3. This figure is a sketch of the SEM photograph of FIG. This figure is a SEM photograph of the surface of the oxide layer of the aluminum nitride substrate having the oxide layer on the surface obtained in the oxidation step of Comparative Example 1. This figure is a sketch of the SEM photograph of FIG. This figure is a SEM photograph of a fracture surface of an aluminum nitride substrate having an oxide layer on the surface obtained in the oxidation step of Comparative Example 1. This figure is a sketch of the SEM photograph of FIG. This figure is a SEM photograph of the surface of the oxide layer of the aluminum nitride substrate having the oxide layer on the surface obtained in the oxidation step of Comparative Example 2. This figure is a sketch of the SEM photograph of FIG. This figure is a SEM photograph of a fracture surface of an aluminum nitride substrate having an oxide layer on the surface obtained in the oxidation step of Comparative Example 2. This figure is a sketch of the SEM photograph of FIG.

Claims (4)

The dew point in the atmosphere from when the temperature is raised to 200 ° C. or higher until the temperature is lowered to less than 1100 ° C. is −50 ° C. or lower, and the oxygen partial pressure is 10 ⁻⁴ atm or lower. A step of obtaining an aluminum nitride substrate having an aluminum oxide layer on the surface by oxidizing the surface at 1100 to 1700 ° C. for 5 hours or more, and forming a wiring pattern made of metal on the aluminum oxide layer of the substrate obtained in the step The manufacturing method of the metallized ceramic substrate including the process to do. The method for forming a wiring pattern made of metal includes a step of covering the entire surface of the aluminum oxide layer with a metal film and a step of removing a part of the metal film coated in the step by ion milling or laser processing. The method described in 1. In the method of manufacturing an aluminum nitride substrate having an aluminum oxide layer on the surface by oxidizing the surface of the aluminum nitride substrate, the temperature of the oxidation is increased from 200 ° C. to lower than 1100 ° C. An aluminum oxide layer is formed on the surface by heating at 1100 to 1700 ° C. for 5 hours or more in an atmosphere having a dew point of −50 ° C. or less and an oxygen partial pressure of 10 ⁻⁴ atm or less. A method for producing an aluminum nitride substrate. An aluminum nitride substrate manufactured by the method according to claim 3 and having an aluminum oxide layer having a thickness of 3 to 15 μm on the surface, wherein a plurality of voids exist in the aluminum oxide layer, and the oxidation Of the plurality of voids existing in the aluminum layer, the proportion of the voids whose diameter is equal to or greater than 0.25 μm in the total number of voids is 5% or more and the total of all voids relative to the area of the aluminum oxide layer including the voids An aluminum nitride substrate having an aluminum oxide layer on the surface, wherein the area occupies 7 to 30%.

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