JPH0585869A - Surface treatment of aluminum nitride ceramic - Google Patents

Abstract

PURPOSE:To perform the title surface treatment designed to improve metallizability by dissolving the surface of an AlN ceramic through chemical etching to form grain boundary grooves of network structure followed by oxidation treatment to produce an Al2O3 film on the surface. CONSTITUTION:An AlN ceramic 1 is first immersed at room temperature in an aqueous NaOH solution to dissolve the surface through chemical etching, thus forming a network structure with grain boundaries and part of the AlN grains etched. Thence, the resulting ceramic surface is put to oxidation treatment to produce a surface treatment layer 2 constituting an Al2O3 layer with grain boundary gaps. The resultant ceramic is then subjected to thick film metallization to form a metallizing layer 5 made up of (A) an oxide layer 3 to be bound to the Al2O3 through fluidization into the gaps and (B) a metal layer 4. And, the surface-treated AlN ceramic is coated with a metal alkoxide to fill the gaps followed by baking under heating to form an oxide film and then metallization to produce a metallizing film with higher adhesivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride ceramic containing aluminum nitride (AlN) as a main component, which is used for a ceramic package and a hybrid IC. A surface treatment method is provided.

[0002]

2. Description of the Related Art Conventionally, alumina (Al ₂ O ₃ ) has been used for ceramics packages and ceramics substrates for hybrid integrated circuits (hybrid ICs).

ICs mounted on ceramics substrates are becoming highly integrated and have high power, and high thermal conductivity is required for the ceramics substrates, and AlN-based nitride ceramics are beginning to be used.

Since AlN ceramics has a thermal conductivity about 10 times higher than that of Al ₂ O ₃ ceramics and further has high resistivity, insulation and low thermal expansion coefficient, it is a ceramic substrate for ceramic packages and hybrid ICs. Is expected as.

In order to apply these ceramics to a ceramic package or a substrate for hybrid IC, a conductor circuit is formed on the substrate. Thick film technology is mainly used for metallization to form this circuit.

In the thick film technology, metal conductor fine particles and oxide fine particles are dispersed in an organic substance to form a paste, which is printed and applied in a circuit shape on a ceramic substrate by screen printing, and then firing is performed to form a conductor circuit. It is a method of forming.

[0007] For example copper Al ₂ O ₃ ceramic substrate (C
u) The method of forming the conductor circuit is as follows.

Cu powder, lead oxide (PbO), boron oxide (B
₂ O ₃ ), an oxide glass powder containing silicon oxide (SiO ₂ ) as a main component, a paste prepared by dispersing in an organic substance containing ethyl cellulose as a main component, printed on an Al ₂ O ₃ ceramics substrate by screen printing, Apply.

This substrate is first treated at 200 to 300 ° C. in a nitrogen gas stream having an oxygen concentration of several tens of ppm to burn off organic substances.

[0010] Continuous treatment is carried out at 800 to 900 ° C in a nitrogen gas stream having an oxygen concentration of several ppm or less to sinter Cu and melt oxide glass to bond Cu and Al ₂ O ₃ ceramics. This oxide is well wetted with the Al ₂ O ₃ ceramics substrate, and good adhesion between the metal conductor and the ceramics substrate is obtained.

However, when this technique is directly applied to the AlN type nitride ceramics substrate, high adhesion strength cannot be obtained. Therefore, a method of forming Al ₂ O ₃ on the surface of this AlN-based nitride ceramics substrate by an oxidation treatment as disclosed in, for example, Japanese Patent Laid-Open No. 61-84037 is disclosed.

Further, JP-A-62-224952 discloses a method of honing the surface of an AlN substrate to have a surface roughness of 2 to 20 μm to increase the adhesion strength. Furthermore, JP-A-62-29
7286 discloses a method of forming a coating of silicon oxide on the surface of an AlN 3 -based nitride ceramics substrate.

[0013]

However, the surface of the AlN-based nitride ceramics substrate only subjected to the oxidation treatment is A
The surface of the l ₂ O ₃ ceramics substrate is structurally and compositionally different, and the conventional thick film paste cannot obtain the adhesion strength comparable to that of the Al ₂ O ₃ ceramics substrate.

The reason is that the Al ₂ O ₃ layer formed on the surface of the AlN-based nitride ceramics substrate by the oxidation treatment is the same as the sintering aid added for the sintering of AlN being present at the grain boundary triple points. , compared to the compositionally a layer consisting substantially only _{Al 2 O 3, Al 2 O} 3 ceramic substrate, sintering aid is present in Al ₂ O ₃ particles between grain boundary glassy state organizations I have

The adhesion of the thick film to the Al ₂ O ₃ ceramics substrate is largely contributed by the glass existing in the grain boundaries. Therefore, in the case of the AlN type nitride ceramics substrate only subjected to the oxidation treatment, the Al ₂ O ₃ ceramics substrate is used. No such adhesion strength can be obtained.

A method of forming a coating of silicon oxide on an AlN-based nitride ceramics substrate is to form a glass layer on the surface to make it adhere to the oxide in the thick film paste.

However, the structure in which SiO ₂ is bonded like a film on the surface of AlN is different from the above-described Al ₂ O ₃ ceramic structure.

The adhesion strength obtained with the Al ₂ O ₃ ceramics substrate is effective not only due to the chemical bonding force between the oxides, but also because the oxides in the thick film paste interact with the grain boundary glass of the substrate. It also depends on the fact that the structure is anchored at the grain boundaries and mechanical bonding force is generated.

The oxide adhered on the structure in which SiO ₂ is bonded in the form of a film on the AlN surface does not anchor at the grain boundaries of the substrate and cannot obtain sufficient strength. During firing, AlN and film-like SiO ₂
There is a risk of film peeling due to the difference in the thermal expansion between and, and the reliability of adhesion is poor.

Further, the surface roughening method by mechanical working such as honing has poor productivity, and the surface condition is not sufficient to obtain the anchoring effect. In addition, surface roughening alone causes AlN
As described above, sufficient adhesion cannot be obtained between the oxide and the thick film paste.

Therefore, the present invention intends to improve the adhesion strength of a thick film by making the surface of the AlN nitride ceramics substantially the same as the Al ₂ O ₃ ceramics in terms of structure and composition. ..

[0022]

In order to make the surface of the AlN-based nitride ceramics have the same structure and composition as the Al ₂ O ₃ ceramics, the present invention performs surface treatment in two or three steps. As described above, the Al ₂ O ₃ ceramic is composed of Al ₂ O ₃ particles and a structure in which oxide glass exists at the grain boundaries, and the oxide glass is composed of magnesium oxide, silicon oxide, calcium oxide, or the like.

On the other hand, in the AlN-based nitride ceramics, the AlN particles are directly sintered to each other, and the added sintering aid has a structure that exists at the grain boundary triple points, and the sintering aid is oxidized by yttrium or calcium. The thing and the carbide are used.

In order to form a grain boundary structure such as Al ₂ O ₃ ceramics in AlN-based nitride ceramics, in the present invention, first, the surface is chemically corroded, for example, the grain boundaries of an AlN sintered body are chemically treated with an alkaline solution. To etch.

AlN is readily soluble in alkali, eg sodium hydroxide solution. Especially the grain boundaries are easily dissolved. this is
It takes advantage of the properties of AlN and in a similar way Al ₂ O ₃
Is difficult to corrode.

Therefore, the corrosion treatment of the present invention is performed before the surface oxidation treatment which is a post-process. By this process AlN
The surface of the system nitride ceramics has a mesh structure with gaps at grain boundaries as shown in FIG. 4 (b) described later.

As a surface roughening method, a method such as honing processing or mechanical grinding can be considered, but in order to obtain a grain boundary structure such as Al ₂ O ₃ ceramics, a groove is selectively formed at the grain boundary. It is necessary to make.

The surface obtained by the chemical corrosion method according to the present invention has a structure having grooves that are very finely entangled with each other in the order of the diameter of ceramic particles. This is difficult to achieve by machining, and this surface treatment can be achieved extremely easily and effectively on an industrial level.

The depth of the corrosion groove is 1 to 2 of the AlN particle diameter.
About twice is preferable. If it is less than that, the effect of the grain boundary oxide produced in the subsequent treatment becomes insufficient, and if it is more than that, it becomes an obstacle to heat conduction.

Following this intergranular corrosion, secondly, a surface oxidation treatment is performed. In this process, an Al ₂ O ₃ layer with a grain boundary gap is formed on the surface. The thickness of the oxide layer is preferably about the thickness of the etched layer of the grain boundaries or slightly thicker than that.

If the oxidation is weaker than this, a sufficient bond cannot be obtained with the subsequent oxide glass, and if oxidation is further performed, it not only hinders heat conduction, but also forms Al ₂ O _{3 produced.}
This is because the boundary between the layer and the AlN 3 substrate may become weak due to the difference in thermal expansion between the layers and the layer may peel off.

When thick film metallization is performed on the AlN system nitride ceramics that has undergone the series of steps described above, the oxide in the thick film paste is melted and flows into the grain boundary gap formed on the substrate surface, and the anchor effect is obtained. And is chemically bonded to Al ₂ O ₃ . Since this metallized structure is the same as that for the Al ₂ O ₃ ceramic substrate, high adhesion strength can be obtained.

Sufficient adhesion can be obtained by the above two steps, but more reliable metallization is performed by further performing the third step. That is, by this process, the AlN-based nitride ceramics has the same structure as the Al ₂ O ₃ ceramics.

First, a metal alkoxide is applied to the above-mentioned surface-treated AlN-based nitride ceramics to fill the intergranular spaces. The metal alkoxide preferably contains an Al ₂ O ₃ ceramics sintering aid or a metal component of an oxide in the thick film paste.

For example, silicon, boron, aluminum, magnesium, calcium, lead, titanium, etc., the metal that can be a glass-forming oxide (silicon, boron, etc.) alone, and the other metal can be a glass-forming oxide. A metal alkoxide compounded with can be used.

The metal alkoxide filled in the grain boundary gap is
It is dehydrated and condensed by heat-oxidation treatment, and then crystallized and vitrified to react with Al ₂ O _{3 on the} surface of the AlN ₃ nitride ceramics. The coating amount of the metal alkoxide is preferably such that it fills the grain boundaries as an oxide.

Further, if the method is one in which the oxide can be filled in the grain boundaries, it is not limited to the use of metal alkoxide, but various experiments have shown that it is easy to penetrate the grain boundaries and form a thin film. Therefore, it was proved that the metal alkoxide was most suitable.

[0038] The same tissue embodied as Al ₂ O ₃ ceramics AlN-based nitride ceramic surface by more than three steps surface treatment, Al ₂ O ₃ ceramics equivalent metallization can be obtained.

[0039]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 (a) shows the metallized structure of the AlN type nitride ceramics according to the present invention. The nitride ceramics 1 has a surface treatment layer 2 on which a metallized layer consisting of a metal layer 4 and an oxide layer 3 is formed.

The metallized layer and the nitride ceramics are firmly bonded via the oxide layer and the surface treatment layer, respectively. Figure 1
(b) and (c) schematically show the details of the connective structure between the surface-treated structure according to the present invention and the metallized layer.

In the nitride ceramic 1 made of a sintered body of aluminum nitride (AlN) 11, an oxide layer 13 made of aluminum oxide (Al ₂ O ₃ ) 12 having a corrosion groove 14 on the surface is formed by the present invention.

The metal layer 4 is bonded to the nitride ceramics 1 by the oxide 3 in the paste penetrating the corrosion groove 14 and bonding to the Al ₂ O ₃ 12.

Further, as shown in FIG. 1 (c), the surface structure in which the oxide 15 is formed in the corrosion groove 14 by the application and oxidation treatment of the metal alkoxide becomes a structure similar to that of Al ₂ O ₃ ceramics, and the paste It can be firmly adhered to the oxide 3 therein.

As a comparative example, FIG. 2 shows an example of a conventional metallized structure. Figure 2 (a) shows a structure in which the surface of AlN nitride ceramics 1 is oxidized and metallized.
(b) shows a structure in which the silicon oxide film 24 is formed on the surface of the AlN nitride ceramics 1 and the metallization is formed thereon.

[0046]

Example 1 The AlN ceramics used in the practice of the present invention was prepared by sintering 1% by weight of yttrium oxide (Y
₂ O ₃ ). Fig. 3 schematically shows the structure of this AlN ceramics 1. Although yttrium oxide exists at the grain boundary triple points, it is omitted in FIG.

This ceramic was immersed in a 1N aqueous solution of aluminum hydroxide (NaOH) at room temperature for 60 minutes to corrode and dissolve the surface. As shown in FIG. 4, the cross section of the ceramics after corrosion had a structure with a grain boundary gap (corrosion groove 14), and its surface had a network groove structure in which the grain boundaries and some AlN grains were corroded. AlN grain 11 is about 5 μm or less and corrosion groove 14
Was about 5 μm, which is about the surface grain size.

Next, this ceramic was subjected to 6 ° C. at 1200 ° C.
Oxidation treatment was performed for 0 minutes to form a surface composed of Al ₂ O ₃ grains 12 having grain boundary gaps as shown in FIG. Oxide layer 1
The thickness of No. 3 was about 5 μm, which is about the surface grain size.

Two copper conductor pastes were added to this ceramic.
Printing was performed with a mm square pattern, and metallization was performed at 900 ° C. for 10 minutes in a nitrogen stream. This copper metallized has a diameter of 0.8
A 90 ° peel test was conducted by soldering a copper wire of mm with eutectic solder. Adhesion strength of the metallized layer, conventional Al ₂ O ₃
Similar to ceramics, the average was 3 kg per 2 mm square area.

As a comparative example, in the same quality AlN ceramics,
Oxidation treatment was performed at 1200 ° C. for 60 minutes, and the same metallization treatment and 90 ° peel test as described above were performed. The adhesion strength was 2 kg on average.

[0051]

Example 2 The AlN ceramics shown in FIG. 5, which was surface-treated according to Example 1, was immersed in a metal alkoxide solution described below for 10 minutes at room temperature.

[0052] Metal alkoxide solution, so as to be approximately 3Al ₂ O ₃ · 2SiO ₂ composition after oxidation sintering silicon alcoholate _{(Si (OC 2 H 5)} 4) and aluminum alcoholates (Al (O
It is a solution of C ₂ H ₅ ) ₃ ) in a water-ethyl alcohol solvent.

20 mm / mi of the ceramic soaked
It was drawn out at a speed of n 2, and subjected to an oxidation treatment at 1200 ° C. for 30 minutes. The surface was made by oxidation, as shown in FIG.
The structure was such that the metal alkoxide oxide 15 was filled between the Al ₂ O ₃ grains 12.

This metal alkoxide oxide 15 is a glass having a composition of about 60 wt% Al ₂ O ₃ 40 wt% SiO _{2 as} a result of analysis.
The ceramic surface was coated with a grain boundary and a film having a thickness of about 2 to 3 μm.

Copper conductor paste was printed on this surface-treated ceramic in a 2 mm square pattern, and the temperature was 900 ° C. × 1.
Metallization was performed in a nitrogen stream for 0 minutes. A copper wire having a diameter of 0.8 mm was soldered to this copper metallization with eutectic solder, and a 90 ° peel test was conducted. The adhesion strength of the metallized layer was 4 kg or more per 2 mm square area.

As a comparative example, the same quality AlN ceramics was immersed in the above-mentioned metal alkoxide solution at room temperature for 10 minutes. This ceramic was taken out at a speed of 20 mm / min and then subjected to oxidation treatment at 1200 ° C. for 30 minutes.

The surface is composed of the same composition as described above.
A film glass having a thickness of μm was produced. This surface-treated ceramic was subjected to the same metallization treatment and 90 ° peel test as described above. Adhesion strength is 3-4kg on average
Met.

[0058]

According to the present invention, the metallizing property of AlN 3 nitride ceramics is improved, and the metallizing technique and method used for the existing Al ₂ O ₃ ceramics can be applied as they are. Therefore, when it is used as a ceramic substrate, the adhesion strength of the thick film or thin film formed thereon is improved, and the reliability of electronic parts is improved.

The principle is that the grain boundaries on the surface of the AlN-based nitride ceramics are corroded and oxides are formed in the gaps to enhance the mechanical binding force of the metallized layer to the ceramic substrate due to the anchoring effect. Secondly, by forming an oxide film on the surface, the chemical bonding force of the metallized layer to the ceramic substrate is improved.

The present invention is characterized in that the oxide film is formed by surface oxidation and, in combination with it, by coating and baking a metal alkoxide.

[Brief description of drawings]

FIG. 1 (a) shows a cross-sectional structure of a surface-treated nitride ceramic when metallized. (b) shows a detailed structure of the surface-treated nitride ceramics and the metallized layer according to the present invention. (c) shows a detailed structure of the surface-treated nitride ceramics and the metallized layer according to the present invention.

FIG. 2A shows a cross-sectional structure when metallization is performed on a nitride ceramic surface-treated by a conventional method. (b) shows the detailed structure of the surface-treated nitride ceramics and the metallized layer by the conventional method.

FIG. 3 shows the structure of AlN ceramics before surface treatment.

FIG. 4 shows the structure when the surface of AlN ceramics is chemically corroded.

[Fig. 5] Chemically corroding the surface of AlN ceramics,
Further, it is a structure when the surface is oxidized, and is an example of the surface-treated nitride ceramics according to the present invention.

[Fig. 6] Chemically corroding the surface of AlN ceramics,
It is the structure formed by the present invention, which shows the structure in which the surface is oxidized and the oxide is coated with the metal alkoxide.

[Explanation of symbols]

1 Nitride Ceramics 2 Surface Treatment Layer 3 Oxide in Paste 4 Metal Layer 5 Metallization Layer 11 AlN Grain 12 Al ₂ O ₃ Grain 13 Oxide Layer 14 Corrosion Groove 15 Metal Alkoxide Oxide 23 Oxide Layer 24 Silicon Oxide Film

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[Procedure amendment]

[Submission date] September 18, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief explanation of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1A is an explanatory diagram showing a cross-sectional structure when metallizing a surface-treated nitride ceramics . (B) is an explanatory view showing a detailed structure of the surface-treated nitride ceramics and the metallized layer according to the present invention . (C) is an explanatory view showing a detailed structure of the surface-treated nitride ceramics and the metallized layer according to the present invention .

FIG. 2 (a) is an explanatory diagram showing a cross-sectional structure when metallizing a nitride ceramic surface-treated by a conventional method . (B) is an explanatory view showing a detailed structure of a surface-treated nitride ceramics and a metallized layer by a conventional method .

FIG. 3 shows the structure of AlN ceramics before surface treatment.
Explanatory drawing.

FIG. 4 is an explanatory view showing a structure when the surface of AlN ceramic is chemically corroded .

FIG. 5 is an explanatory view of a structure when the surface of AlN ceramic is chemically corroded and the surface is further oxidized, which is an example of the surface-treated nitride ceramics according to the present invention.

FIG. 6 is an explanatory view of a structure formed by the present invention, showing a structure in which the surface of AlN ceramics is chemically corroded, the surface is oxidized, and further an oxide coating with a metal alkoxide is performed.

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1 (a)]

[Figure 1 (b)]

[Fig. 1 (c)]

[Figure 2 (a)]

[Fig. 2 (b)]

[Figure 3]

[Fig. 4 (b)]

[Fig. 4 (a)]

[Figure 5]

[Figure 6]

Claims (2)

[Claims] 1. A surface treatment of aluminum nitride ceramics, characterized in that the surface of aluminum nitride is dissolved by chemical corrosion to form a mesh-shaped grain boundary groove, and then oxidation treatment is performed to form aluminum oxide on the surface. Method. 2. A surface treatment method for an aluminum nitride ceramics, which comprises applying the surface treatment of claim 1 and then coating a metal alkoxide and firing the coating to coat the surface of the substrate with an oxide.