JPH02188481A - Method for metallizing aln ceramics - Google Patents

Abstract

PURPOSE:To improve the adhesive strength of a metallizing layer to AlN ceramics by forming the layer on the surface of the ceramics by the vapor deposition of Cu and irradiation with ions of an inert gas. CONSTITUTION:Cu is evaporated from an evaporating source 5 and deposited on an AlN ceramic substrate 1 set in a vacuum chamber 2. At the same time, the substrate 1 is irradiated with ions of an inert gas 6 from an ion source 4. This inert gas 6 is selected among He, Ne, Kr, Xe and N2. A Cu metallizing layer is formed on the surface of the AlN ceramic substrate.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an AI! The present invention relates to a method of metallizing N ceramics.

[Conventional technology]

As silicon ICs become smaller and more dense, technology for mounting elements in hybrid IC circuits and printed circuit boards at a higher density is progressing.

Recently, techniques have been proposed for wiring three-dimensionally and for mounting elements three-dimensionally.

As elements are mounted in such a high density, countermeasures against heat generation from integrated circuit elements, resistive elements, and wiring conductors have become an important issue.

Conventionally, materials such as printed circuit boards are made using A P, t O
c (alumina) has been used, but this AI! t
Os has low thermal conductivity (20 W/mK), and therefore cannot dissipate heat from elements etc. well.

This A j! As an alternative substrate material to tO3, AI due to its good thermal conductivity! , N ceramics are attracting attention. The main properties of /IN ceramics and Af, O, are shown in Table 1 below.

(Margin below) Table 1 However, this AAN ceramic has a relatively small coefficient of thermal expansion of 4.4 x 10-'/'C, which is close to that of silicon (coefficient of thermal expansion is 3.6 x 10-'PC). Copper, silver, gold (thermal expansion coefficient: 15-20 x 10-'/'C)
When the surface is metallized and this metallized layer is used as a wiring conductor, etc., if the metallization is performed at a high temperature, there is a problem that distortion occurs due to the difference in coefficient of thermal expansion when cooling to room temperature. Furthermore, this AffiN ceramic has poor wettability with most metals (and is difficult to metalize).

/IN Conventionally, the metallization of the ceramic substrate surface is
This is done using the following methods.

(2) The surface of the AffiN ceramic substrate is oxidized to Al z O's at 1000''C or higher, and a metallized layer is formed on this oxidized layer by the Mo-Mn method or the like.

■A! Ti is deposited on the surface of the NAl mix substrate, and PT or Au is deposited thereon and heat treated to form a metallized layer. According to this method, the adhesion strength of the metallized layer is 2
It is estimated that the bond strength is about 5 kg/sum. This adhesion strength is mainly caused by active Ti reacting with the AlN ceramic substrate and diffusing into the substrate.

[The problem that the invention aims to solve]

However, method (2) above involves a high-temperature process treatment of 1000'C or more, which leads to high costs, and the Mo-Mn method involves applying a paste of mixed powder of Mo and Mn to the surface of the A2N ceramic substrate. After coating, it is necessary to heat the coating to about 1500''C in a superhumidified hydrogen atmosphere, which causes distortion due to the above-mentioned difference in thermal expansion coefficients, resulting in poor yield and, as a result, increased costs.

In addition, method (2) above requires heat treatment (300 to 500'C) to react Ti with AffiN ceramics and diffuse it into the AffiN ceramic substrate, which also causes distortion due to the difference in thermal expansion coefficient. . Furthermore, since soldering or brazing cannot be applied to Ti,
As mentioned above, expensive PT and Au are vapor-deposited, resulting in an increase in cost.

Electroless plating is a typical technique for metallizing near room temperature, but in this electroless plating method, the adhesion strength of the metallized layer to the AlN ceramic substrate is as low as 2 kg/11111z, and the chain properties are poor and Yield is also poor.

In order to solve the above-mentioned problems, the present inventors previously proposed in Japanese Patent Application No. 63-254531 a Cu metallized layer with relatively high adhesion strength to the surface of a /IN ceramic substrate without high-temperature treatment. We propose a method for forming This method involves irradiating Ar ions onto the surface of the AffiN ceramic substrate while depositing Cu.
A mixed layer of this AlN ceramic substrate material and the vapor-deposited Cu and Ar is formed on the surface of the ceramic substrate, and the metallized layer is heated by the action of this mixed layer.
1. This is a method to firmly adhere to the surface of the N-ceraminx substrate. However, in this method, the Ar ions are directed to the substrate surface in excess (10"/cm") at room temperature or below.
When irradiating the above), the substrate surface and the metal layer (Cu vapor deposited layer)
Ar gas remains at the interface. For this reason, for example, when a metallized AlN ceramic substrate is used as a printed circuit board, the residual Ar gas diffuses due to heat generated by elements mounted on the printed circuit board, forming voids, and causing deterioration of the metallized layer. becomes. For this reason, the adhesion strength of the metallized layer is determined by the amount of Ar ion irradiation at which the voids are not formed, and there is a problem in that it is not always possible to obtain the desired adhesion strength.

One possible way to solve this problem is to irradiate metal (Aj!, Ti, Cr, etc.) ions instead of the Ar ion irradiation, but at present there are no industrially practical metal ion sources. Not developed.

An object of the present invention is to provide a method for metallizing AffiN ceramics that can solve the above-mentioned technical problems and improve the adhesion strength of the metallized layer.

[Means to solve the problem]

The method of metallizing AlN ceramics of this invention is based on C
evaporation of u and inert gas group He, Ne.

The above-mentioned Af! , is characterized by forming a metallized layer on the surface of N ceramics.

(Function) According to the configuration of the present invention, by using the vapor deposition of Cu in combination with the irradiation of one or more inert gas ions selected from the inert gas group He, Ne, Kr, Xe, and Nz, Al
A metallized layer is formed on the N ceramic surface. That is, ions of an inert gas other than Ar are irradiated toward the AlN ceramics.

The deposited Cu is pushed into the AfiN ceramics by inert gas ions, and in this way, a metallized layer having a mixed layer of the AlN ceramics, Cu, and the inert gas is formed on the surface of the AlN ceramics. . The mixed layer can have sufficient adhesion strength to the AffiN ceramics, so that the metallized layer as a whole adheres sufficiently firmly to the surface of the AlN ceramics.

The above-mentioned metallization process is carried out at room temperature, and therefore distortion does not occur due to the difference in thermal expansion coefficient between Cu and AlN ceramics, which are the materials of the metallized layer, and peeling of the metallized layer does not occur. It never happens.

In this invention, as described above, AlN ceramics are irradiated with ions of an inert gas other than Ar.
When using an inert gas (He or Ne) with an atomic radius smaller than the The inert gas remaining at the interface can be easily dissipated by heating from room temperature to about 100°C, and therefore the formation of voids at the interface can be easily prevented.

On the other hand, when an inert gas with a larger atomic radius than Ar is used, these inert gases have a lower diffusion rate than Ar, so they do not diffuse when heated from room temperature to about 100°C, and therefore voids are formed at the interface. is never formed. Thereby, the amount of irradiation of the inert gas can be made relatively large, and the desired adhesion strength of the metallized layer can be obtained.

Furthermore, for example, when AlN ceramics is irradiated with Ne ions at a low acceleration energy of 10 keν or less,
Since the mass of Ne ions is close to the mass of N atoms, N atoms are selectively sputtered on the AnN ceramic surface, resulting in AI! on the AlN ceramic surface. , the state is enriched with atoms, and therefore the deposited Cu and Al
The bonding force with N ceramics can be increased.

In addition, for example, light elements such as He and Ne have a relatively large implantation depth from the surface of AffiN ceramics, which makes it possible to increase the layer thickness of the mixed layer (and improve the adhesion strength of the metallized layer). In addition, by increasing the layer thickness of the mixed layer, for example, when the surface of an Ajl!N ceramic substrate is metalized and used as a printed circuit board, the difference in thermal expansion between Cu and AlN ceramics can be reduced due to thermal cycles in the actual usage environment. Even if
Since this difference in thermal expansion can be absorbed by the thick mixed layer, peeling of the metallized layer is prevented.

[Embodiment] FIG. 2 is a conceptual diagram showing the basic configuration of a thin film forming apparatus according to an embodiment of the present invention. Should be metalized/IN
The ceramic substrate 1 is fixed to the surface of a sample holder 3 that is rotated around an axis 11 within a vacuum chamber 2 .

A packet type ion source 4 is provided opposite the sample holder 3, and an electron beam heating type evaporation source 5 for evaporating Cu is provided in the middle.

In the arc chamber 9 provided for the ion 1II4, there is a
Inert gas other than r gas, that is, inert gas group He,
One or more inert gases selected from Ne, Kr, Xe, and N2 are introduced. In the arc chamber 9, an arc discharge is caused between the filament 7 and the plasma electrode 8 to dissociate the inert gas and generate plasma, and inert gas ions are extracted from this plasma by the suppression electrode 10 and the extraction electrode 11. The specimen is accelerated toward the specimen holder 3 and taken out.

12 is a film thickness monitor for measuring the film thickness of the metallized layer deposited on the surface of the substrate 1; 13 is a film thickness monitor for measuring ions 1jJ, 4;
This is an ion current monitor that detects the beam current of the ion beam from the ion beam.

With such an FM film forming apparatus, Ajl! In metallizing the surface of the N ceramic substrate 1, Cu is evaporated from the evaporation source 5 and the Cu is deposited,
The ion source 4 irradiates the above-mentioned inert gas ions.

At this time, the degree of vacuum in the vacuum chamber 2 is 10-'Torr.
and the gas pressure of the inert gas is I
X 10-'Torr. The acceleration energy of the inert gas ions is 10 eV to 50 keV. In this way, the material of this substrate 1 (
AI! , N), Cu, and an inert gas are formed.

The formation of this mixed layer is shown in a simplified manner in FIG. 1, where a indicates AI! , N ceramic substrate 1, b
is the above-mentioned mixed layer, and C is a vapor deposited layer in which an inert gas and CU are mixed. Note that d is an inert gas ion and e is a Cu vapor.

The Cu evaporated material e evaporated at an arbitrary rate is 10 eV to 50
It is mixed with inert gas ions accelerated by keν on the surface of the substrate 1. At this time, Cu atoms are sputtered or pushed into the substrate 1 by the accelerated inert gas ions. In this way, the above-mentioned mixed layer is grown (this mixed layer firmly adheres to the substrate 1, and the Cu vapor-deposited NC firmly adheres to the mixture 1b).

The amount of inert gas ion irradiation per unit time and unit area and the number of Cu atoms to be deposited are set so that the Cu deposition rate is slightly larger than the svanta rate of Cu by inert gas ions. Determined by As a result, Cu1l becomes the above-mentioned A! It will grow on the surface of the N ceramic substrate 1.

There is an optimum value for the number of Cu atoms to be injected into the AlN ceramic substrate l. The higher the acceleration energy of the inert gas ions, the more the number of Cu atoms forced into them increases due to cascade collisions, but when the energy of the inert gas ions is excessively high, the inert gas ions pass through the Cu film. Therefore, Cu atoms cannot be pushed into the group Fi1.

The evaporation of Cu and the irradiation of inert gas ions on the surface of the substrate 1 may be performed simultaneously or alternately, that is, by using the evaporation of Cu and the irradiation of inert gas ions together, It is possible to form a mixed layer firmly adhered to the substrate 1.

The thickness of the mixed layer is kept within a range that allows inert gas ions to reach the substrate 1, and the subsequent layer thickness of Cu evaporated Nc is set to 500 to 10,000 to prevent external conditions from affecting the mixed layer.
Be with people.

The Cu evaporated Nc can be formed in close contact with the mixed layer, and the CuM deposited layer forms a metallized layer. This metallized layer has sufficient adhesion strength between the substrate 1 and the mixture 1b, and between the mixed Nb and Cu evaporated layers, so that it is firmly adhered to the substrate 1 as a whole. Further, the formation of this metallized layer does not involve a high-temperature process, so distortion caused by the difference in thermal expansion coefficient between AlN and Cu, etc., and peeling of the metallized layer do not occur.

Furthermore, since AffiN ceramics has high thermal conductivity as mentioned above, the metalized substrate 1 can be used as an IC.
When applied to a pan cage, etc., it becomes possible to effectively dissipate heat from resistance elements, semiconductor elements, wiring conductors, etc., and therefore the functions of each element can be performed well. It is possible to satisfactorily increase the degree of integration of integrated circuit elements in which dissipation is important.

In this embodiment, an inert gas other than Ar is used as the inert gas, but for example, inert gases (He and Ne) having a smaller atomic radius than Ar have a diffusion rate of A.
r, thereby making the A2N of the metallization layer
When the irradiation amount of inert gas ions is set excessively in order to improve the adhesion strength to the ceramic substrate 1, for example, when the irradiation amount is set to 10I'1/cm'' or more,
Even if the inert gas remains at the interface between the metallized layer and the substrate 1, the remaining inert gas can be easily dissipated by heating at a relatively low temperature of about room temperature to 100°C. Therefore, the formation of voids at the interface can be easily prevented, and for example, the metallized A! N ceramic base if 1 to printed circuit board or IC
When applied to a package or the like, the metallized layer is prevented from deteriorating due to heat generated by semiconductor elements, resistive elements, etc. By increasing the amount of inert gas irradiation in this way, it is possible to improve the adhesion strength of the metallized layer to the AlN ceramic substrate 1.

In addition, inert gases (for example, Kr, Xe) whose atomic radius is larger than Ar have a low diffusion rate, so if ions of such inert gases are excessively irradiated toward the surface of the AfN ceramic substrate Even if the inert gas remains at the interface between the metallized layer and the A42N ceramic substrate 1, this inert gas will remain at room temperature to 100°C.
It does not easily diffuse when heated at a relatively low temperature. Therefore, when the metallized AlN ceramic substrate 1 is applied to a printed circuit board, an IC package, etc., even if a semiconductor element or a resistor element generates heat, voids will not be formed at the interface and the metallized layer will not deteriorate. Therefore, by increasing the irradiation amount of the inert gas, the adhesion strength of the metallized layer to the Aj2N ceramic substrate 1 can be increased without causing any problems.

In addition, although the mechanism has not been elucidated, a selective sputtering phenomenon occurs.
When irradiating toward the surface of the N ceramic substrate 1, the AI of the metallized layer! , N may increase the adhesion strength to the ceramic substrate 1.

For example, when Ne is used as the inert gas, Niha, N
Since the mass of the atom is close to the mass of the Ne ion, N
Atoms are selectively spun, and as a result, the surface of the AfN ceramic substrate 1 becomes rich in Hel atoms. This increases the bonding force between the deposited Cu and the surface of the AffiN ceramic substrate 1, and as a result, the adhesion strength of the metallized layer can be increased.

For example, in Japanese Patent Application Laid-Open No. 63-252976,
Heating AρN ceramics to high temperature in vacuum, /IN ceramics surface,! However, the method of this example allows similar A2N ceramic surface treatment to be performed at room temperature, and is extremely advantageous from the viewpoint of production costs.

Furthermore, in the case of light element inert gases (He, Ne), AgN
There is an advantage that the depth of implantation into the surface of the ceramic substrate 1 becomes deep, and as a result, the layer thickness of the above-mentioned mixed layer C can be made relatively large. Generally, metallized AlN
In a practical environment where the ceramic substrate 1 is used as a printed circuit board, an IC package, etc., thermal cycles occur due to heat generation of elements, etc.
When it is about 2 atomic layers, A! N ceramics substrate 1
A! The difference in thermal expansion between N ceramics and Cu causes peeling of the metallized layer.

If the light element inert gas ions are implanted into the /IN ceramic substrate 1, the implantation depth is deep, so it is possible to form a mixed layer C having a large layer thickness of about several hundred layers. As a result, the difference in thermal expansion can be absorbed by the mixed layer C having a large layer thickness, and peeling of the metallized layer can be prevented.

As described above, according to this example, by using inert gas ion irradiation other than Ar ions and Cu vapor deposition in combination, a metallized layer with higher adhesion strength than when using Ar ions can be formed. Moreover, it is possible to prevent voids from forming in this metallized layer and suppress its deterioration.

Test examples by the inventor of the present invention are shown below.

The degree of vacuum in the vacuum chamber 2 is 10-'Torr, and H
Inert gas ions of e, Ne, and Xe are used.

This inert gas ion irradiation increases the acceleration energy by 5~
The injection voltage is set to 25 keV, and the injection is stopped when the peak of the implantation depth of the inert gas ions reaches the interface of the substrate 1. For each inert gas ion, the inert gas ion irradiation dose was set to 10” (
Pieces/C19,10"(pieces/cm"), 10 If
f (pcs/cu+') (7) Set in 3 ways to obtain AfN
Each sample was prepared by metallizing the ceramic substrate 1. An aluminum rod was adhered to the surface of the metallized layer of this sample using an epoxy adhesive, and a tensile test was conducted. The results are shown in Table 2 below.

Table 2 shows the adhesion strength (kg/ml) for each ion species He, Ne, and Xe when the ion irradiation dose is set in the three ways described above. The value is 560°C for the metallized layer of each sample.
This is the adhesion strength when vacuum annealing treatment is performed for X3 minutes. In this Table 2, the values of adhesion strength shown with the inequality sign ">j" indicate that the adhesive mentioned above was broken during the tensile test, and therefore the adhesion strength of the metallized layer to the substrate 1 is low. Intensity indicates that it is greater than the number that follows it.

(Margin below) Table 2 From the results shown in Table 2, it is understood that the adhesion strength can be improved by increasing the irradiation amount of inert gas ions. Since no deterioration in adhesion strength was observed in this test example, it is understood that the metallized layer had sufficient heat resistance (560°C) in this test example.

Furthermore, the inventor of the present invention has also conducted heat resistance tests regarding soldering and brazing, and has confirmed that the metallized layer in the test example can sufficiently withstand the temperatures of soldering and brazing.

In the above embodiment, the inert gas ions were irradiated only when forming the mixed layer and not when forming the vapor deposited layer C, but the inert gas ions were irradiated also when forming the vapor deposited layer C. You can do it like this. However, in this case, the growth of the metallized layer is suppressed by the sputtering action of the inert gas ions, and lattice defects may be generated in the metallized layer, which may lead to deterioration in the strength of the metallized layer.

In the above embodiments, He and Ne are used as the inert gas.

Although the case where Xe and Kr are used has been described, N2 may also be used, and in such a case, an effect corresponding to the atomic radius etc. can be obtained.

Further, the number of inert gases used is not limited to one type, and irradiation with two or more types of inert gas ions may be performed simultaneously with the vapor deposition of Cu.

〔Effect of the invention〕

As described above, according to the method of metallizing AAN ceramics of the present invention, even if the amount of inert gas ions is set excessively, voids can be prevented from being formed at the interface between the AlN ceramics and the metallized layer. Therefore, the desired adhesion strength of the metallized layer can be obtained by increasing the irradiation amount of the inert gas ions.

In addition, for example, if Ne ions whose mass is similar to N atoms are irradiated with low acceleration energy, N atoms on the surface of AlN ceramics can be selectively sparged, and this will cause the surface of AlN ceramics to become AlN.
This can make it easier for the deposited Cu to bond. This improves the adhesion strength of the metallized layer.

Furthermore, by irradiating light element inert gas ions, Al
A relatively thick layer of mixture 1i (A
f! Since a mixture N) of N, Cu, and an inert gas can be formed, the difference in thermal expansion between Al2N ceramics and Cu can be absorbed by this mixed layer. As a result, when a metallized A42N ceramic substrate or the like is applied to a printed circuit board, an IC package, or the like, it is possible to prevent the metallized layer from peeling off due to thermal cycles in the actual usage environment.

[Brief explanation of the drawing]

Figure 1 shows metallized /
FIG. 2 is a conceptual diagram showing the basic structure of a thin film forming apparatus according to an embodiment of the present invention. 1... AlN ceramics substrate, 4... ion source,
5... Evaporation source, a.../IN ceramics substrate, b
...Mixed layer, C...Cu vapor deposited layer, d...Inert gas ion, e...Cu evaporated substance Fig. 1 Fig. 2

Claims (1)

[Claims] A method of metallizing the surface of AlN ceramics with Cu, which involves vapor deposition of Cu and inert gas group He, Ne.
, Kr, Xe, and N_2 to form a metallized layer on the surface of the AlN ceramic.
Metallization method for N ceramics.