JPH0453836B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a method for metallizing a ceramic sintered body containing aluminum nitride as a main component.

[Prior art and its problems]

Up until now, alumina has been exclusively used as ceramics for substrates and packages that support semiconductors, but due to its low thermal conductivity, heat generation and heat dissipation from semiconductor elements becomes a problem in highly integrated and high-density packaging. It is not suitable as a substrate for On the other hand, aluminum nitride (AlN), which contains 0.5 to 5.0% by weight of yttrium oxide or calcium oxide, has high volume resistivity, high dielectric strength voltage, low dielectric constant, and high thermal conductivity similar to alumina. (5 to 8 times that of alumina), low coefficient of thermal expansion (close to silicon), and high strength (about twice that of alumina), so power ICs, LSIs, and VLSIs where element heat generation and heat dissipation are problems. It is seen as a promising substrate or package material.

On the other hand, when ceramics are used as a semiconductor substrate, it is necessary to metalize them to form conductor circuits. This metallized layer is required to be strongly bonded to the ceramic substrate, to be dense, and to have excellent bonding properties and airtightness when mounting elements. For alumina, a mixed powder of molybdenum or tungsten powder, which is a high-melting point metal, and manganese or titanium powder, which is an activated metal, is applied to the surface of the alumina and heated at a temperature of 1300℃ to 1550℃ in a slightly oxidizing atmosphere. The metallization method of firing is known as the so-called high melting point metal method or Telefunken method.

The following three methods are conventionally known as methods for metalizing AlN substrates. That is, (1) AlN is heated to 1000°C to 1400°C, oxidized to form an alumina (Al ₂ O ₃ ) layer, then a copper plate is placed on the AlN substrate, and the oxygen partial pressure and temperature are adjusted.
A method of metallizing by performing bonding processing in an electric furnace that precisely controls the eutectic temperature of the Cu-O system.

(2) A method in which a paste containing glass components such as gold, silver-palladium, or copper is applied to the surface of an AlN substrate, and then the paste is fired to metallize it.

The substrate produced by method (1) above is DBC (Direct Bond
However, strict control of oxygen partial pressure and temperature is required during the bonding process, and slight differences in condition settings can cause variations in bonding strength and airtightness between the AlN substrate and the copper layer. Easy to occur. Furthermore, since the thermal expansion coefficients of AlN and copper are significantly different, both may become distorted due to the influence of ambient temperature, causing reliability problems. Method (2) is the so-called thick film method, but the bonding strength between the substrate and the metallized layer is
It was at a level of 1.2 to 2.0 Kg/mm ² , and the soldering and brazing properties were poor, and the airtightness was also insufficient.

Therefore, in order to put AlN into practical use as a highly thermally conductive semiconductor substrate, it is necessary to establish a highly reliable and economical metallization method.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned drawbacks, and its object is to provide a method for metallizing aluminum nitride ceramics that is excellent in bonding strength and airtightness and is also economical.

[Key points of the invention]

In the invention, after forming a silicon oxide film on the surface of aluminum nitride ceramics,
This goal was achieved by metallizing aluminum nitride ceramics by coating them with a mixed powder of a high melting point metal and an activated metal and firing them in a weakly oxidizing atmosphere.

In other words, aluminum nitride ceramics are coated with a mixed powder of a high-melting point metal such as molybdenum or tungsten and an activated metal such as manganese or manganese-titanium, and hydrogen gas is bubbled into water to form a weak acid consisting of a hydrogen-steam gas mixture. Although a good metallized layer cannot be obtained even if fired in a oxidizing atmosphere, a film of silicon oxide is formed on the AlN surface and then coated with a mixed powder of a high melting point metal and an activated metal. It has been discovered that a good metallized layer can be obtained by firing inside the molten metal. In other words, the Telefunken method, which is an alumina metallization method, cannot be directly applied to AlN, but if the AlN surface is converted to silicon oxide, the Telefunken method can be applied as is.

[Embodiments of the invention]

Next, embodiments of the present invention will be described based on the drawings. Aluminum nitride ceramics 11
The (AlN) used contained 1% by weight of yttrium oxide as a sintering aid and was produced by a hot pressing method. A water-isopropyl alcohol solution or a water-ethyl alcohol solution of silicon alcoholate (Si(OC ₅ H ₁₁ ) ₄ ) is applied to the surface of this AlN using the dip method, and heat-treated at a temperature of 150°C to 500°C to form a 0.8 μm thick layer. A thick and dense silicon oxide film 12 strongly bonded to AlN was formed. In addition to the dip method, a spray method can be used as the coating method, and the thickness of the silicon oxide film can be arbitrarily controlled by the coating method or the number of coatings. Silicon oxide is formed through the following chemical reaction.

Si(OC ₅ H ₁₁ ) ₄ ) +4H ₂ O→Si(OH) ₄ +4C
₅ H ₁₁ OH……(1) Si(OH) ₄ →SiO ₂ +H ₂ O↑ ……(2) Equation (1) is the hydrolysis reaction in the alcoholate solution, and Equation (2) is the reaction during heat treatment. This is the reaction. In the case of the present invention, silicon oxide having a thickness of around 1 μm is sufficient to achieve the purpose.

A silicon oxide film can be formed on the AlN surface by physical methods such as sputtering. On the other hand, 80 parts by weight of commercially available molybdenum and manganese powder
The slurry was weighed at a ratio of 20%, an organic solvent and a binder were added to it, mixed and ground using a mill to form a slurry with a particle size of 5μm or less, and then printed onto a silicon oxide film with a thickness of 18μm using a screen printing method. The mixed powder 13 of molybdenum and manganese was coated by coating. This was fired in an electric furnace while flowing hydrogen bubbled through water at a temperature of 50°C. The temperature was raised at a rate of 300°C/hour, and the maximum temperature was maintained at 1400°C for 1 hour. The thickness of the obtained molybdenum metallized layer 15 is 11μ
It was m. Thereafter, nickel plating was applied to the metallized layer 15 to a thickness of 4 μm using an electroless plating method. This is done in a mixed atmosphere of hydrogen and nitrogen.
Heat treatment was performed at 820°C for 15 minutes, and inspection was conducted to check for peeling of the plating, blistering, etc., and it was confirmed that there were no defects. Next, nickel-plated AlN substrate and thickness 3
Fe--Ni alloy (42% by weight of nickel) of 2 mm thick was joined using silver solder (BAG-8), and its airtightness was examined by a helium leak test. The amount of helium leaked from the joint was less than 1×10 ^-8 (atm·ml/sec), and the airtightness was good. Furthermore, a copper wire with a diameter of 0.5 mm was soldered onto the plated AlN substrate using eutectic solder (40%Pb-60%Sn), and a tensile test was performed on the wire. In this test, all the copper wires were broken, and there was no breakage at the interface between the metallized layer 15 and the AlN substrate, or at the interface between the metallized layer and the plating. The strength per unit area when the copper wire breaks is 25
Kg/mm ² , and it was found that the interface between the AlN substrate and the metallized layer according to the method of the present invention has a strength of 25 Kg/mm ² or more.

Next, another embodiment of the invention will be described. Commercially available molybdenum, manganese and titanium powders are weighed in a weight ratio of 80:15:5, an organic solvent and a binder are added, and the mixture is ground using a milling machine to contain powders with a particle size of 5 μm or less. Adjusted slurry. This is the first
On the silicon oxide film 12 of the aluminum nitride ceramic 11 treated under the same conditions as in the example,
A film of mixed powder of molybdenum, manganese, and titanium was formed by printing to a thickness of 20 μm, and fired at a temperature of 1450° C. for 1 hour in a hydrogen gas atmosphere through which water at 20° C. was passed to form a molybdenum metallized layer.
The characteristics of this metallized layer were evaluated in the same manner as in the first example. The results were as good as in the first example.

Although molybdenum is used as the high melting point metal in the above examples, it has been experimentally confirmed that the same results as in the case of molybdenum can be obtained even when tungsten is used.

In the weakly oxidizing atmosphere described in the above example, high melting point metals such as molybdenum or tungsten are not oxidized, but activated metals such as manganese and titanium are oxidized to manganese oxide and manganese oxide, respectively. Titanium etc. On the other hand, it is presumed that the silicon oxide film 12 facilitates the reaction of oxidizing aluminum nitride ceramics AlN into alumina (Al ₂ O ₃ ) in a weakly oxidizing atmosphere, and for this reason, the vitrification reaction described later is difficult. It becomes possible. The generated intermediate layer 14 (possibly an alumina layer) undergoes the above-mentioned manganese oxide, titanium oxide, or silicon oxide reaction to form a glass layer 16, which fills the gap between the molybdenum powder 17 and forms a metallized layer 15. Since this glass layer 16 is chemically bonded to the intermediate layer 14, the bonding strength between the metallized layer 15 and the aluminum nitride ceramic 11 is high. Furthermore, the metallized layer 15 is hermetically bonded to the aluminum nitride ceramic 11 so that the glass layer densely fills the gaps between the molybdenum powders 17.

〔Effect of the invention〕

In this invention, a silicon oxide film is first formed on the surface of aluminum nitride ceramics, and then a mixed powder film of a high melting point metal and an activated metal is formed, and then fired in a weakly oxidizing atmosphere. Silicon oxide facilitates the transformation of aluminum nitride ceramics into an intermediate layer, which enables a vitrification reaction between the activated metal oxide and the intermediate layer formed on the surface of aluminum nitride ceramics, resulting in excellent airtightness and bonding strength. This results in the formation of a large metallized layer. In addition, this method allows the industrially established high melting point metal method (or Telefunken method) used for metallizing alumina to be used as is, making it possible to use existing equipment and making it an economical metallization method. It can be said that there is.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an aluminum nitride ceramic before forming a metallized layer according to an example of the present invention, and FIG. 2 is a schematic cross-sectional view showing an aluminum nitride ceramic on which a metallized layer is formed according to an example of the present invention. 11... Aluminum nitride ceramics, 12
... Silicon oxide coating, 13... Molybdenum and manganese mixed powder coating.

Claims (1)

[Claims] 1. A film of silicon oxide is formed in advance on the surface of aluminum nitride ceramics, and then a film of mixed powder of a high melting point metal and an activated metal is formed, and the film is fired in a weakly oxidizing atmosphere. A method for metallizing aluminum nitride ceramics. 2. A method for metallizing aluminum nitride ceramics according to claim 1, wherein the aluminum nitride ceramics contains yttrium oxide. 3. A method for metallizing aluminum nitride ceramics according to claim 1, characterized in that a silicon alcoholate solution is applied and heated and fired to form a silicon oxide film.