JPH07161871A - Circuit board - Google Patents

Abstract

PURPOSE:To improve the fixation and prevent the drop of reliability caused by a circuit board by providing an AlTiN layer, which is epitaxial to an AlN board and corresponds to the mutual diffusion layer for an AlN board and a Ti layer, between the AlN board and the Ti layer. CONSTITUTION:An AlTiN layer 2 epitaxial to the AlN on the surface is provided on the board (AlN board) 1 mode of AlN. A conductive layer 4 is provided through a Ti layer 3 on this AlTilN layer 2. That is, since an AlTiN layer 2 corresponding to the mutual diffusion layer for these is provided between the AlN board 1 and the Ti layer 3, the AlN board 1 sticks fast to the AlN board 1 through the AlTiN layer 2. Moreover, since the AlTiN layer 2 is epitaxial to the AlN board 1, the interface defects such as lattice irregularity at the interface between the AlN board 1 and the AlTiN layer 2, etc. decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board using aluminum nitride (AlN) as a board material.

[0002]

2. Description of the Related Art In recent years, a large-scale integrated circuit formed by integrating a large number of transistors, resistors, etc., on one chip in an important part of a computer or communication equipment so as to achieve an electric circuit ( LSI) is frequently used. Therefore, the performance of the entire device is largely linked to the performance of the LSI alone.

The performance improvement of the LSI itself can be realized by increasing the degree of integration, that is, by miniaturizing the elements. Due to such miniaturization, in recent computer systems, elements having a clock frequency of 100 MHz and a power consumption of 30 W or more per chip are being used.

A substrate on which such an element is mounted is required to have a high signal propagation speed and good heat dissipation, and improving both characteristics is indispensable for reflecting the element characteristics on the system characteristics. is there.

Of these, when attention is paid to heat dissipation, there are AlN, BN, diamond, diamond-like carbon, BeO, etc. as candidates for the substrate material. However, the ease of the manufacturing method, the influence on the environment, the heat dissipation characteristics, etc. Considering this, use of AlN is preferable.

By the way, as a method of manufacturing a circuit board, a multi-layer wiring board by a co-firing method is generally used, but it is necessary to form a thin film circuit on the surface of the board due to the recent demand for higher density.

TiN / N is used as a wiring material for thin film circuits.
i / Au, Ti / Pt / Au, Ti / Cu, Cr / C
Multi-layer metal films such as u and Ti / Al are used. These wiring materials are also used as a metallization layer for joining metal components such as input / output pins, leads, and sealing rit by soldering or brazing heat treatment.

When an attempt is made to bond a metal component to an AlN circuit board by using such a multilayer metal film as a metallized layer, the heating at the time of this bonding causes a linear thermal expansion between the multilayer metal film as a wiring layer and the AlN circuit board. Due to the difference in the coefficient,
Residual stress and various defects occur. As a result, the adhesion between the multi-layer metal film as the wiring layer and the AlN circuit board becomes insufficient, and the reliability deteriorates. Such a problem also occurs in the heat treatment in the subsequent process.

[0009]

As described above, TiN / Ni / Au and Ti / Pt / are used as wiring materials for thin film circuits.
Multi-layer metal films such as Au, Ti / Cu, Cr / Cu, and Ti / Al were used, but since these multi-layer metal films were also used as metallization layers, in heating at the time of joining metal parts, etc., Multi-layer metal film as wiring layer and AlN
There is a problem that the adhesion to the substrate is reduced and the reliability is reduced.

The present invention has been made in view of the above circumstances, and an object thereof is to improve the adhesion between a multilayer metal film and an AlN substrate to provide a highly reliable circuit board. is there.

[0011]

In order to achieve the above object, a circuit board of the present invention is formed epitaxially on a substrate (AlN substrate) made of aluminum nitride and aluminum nitride on the surface of the AlN substrate. First metal layer (AlTiN
Layer), a second metal layer (Ti layer) made of titanium and formed on the AlTiN layer, and a conductive layer formed on the Ti layer.

[0012]

According to the present invention, since the AlTiN layer corresponding to the interdiffusion layer is provided between the AlN substrate and the Ti layer, the AlN substrate is provided with the AlTiN layer via the AlTiN layer.
It comes to firmly adhere to the 1N substrate.

Since the AlTiN layer is epitaxially formed on the AlN substrate, the AlN substrate and the A
Interface defects such as lattice mismatch at the interface with the 1TiN layer are reduced, and the adhesion strength between the AlN substrate and the AlTiN layer becomes strong. Further, stress concentration near the interface between the AlN substrate and the AlTiN layer is relaxed. This is AlN
It contributes to maintain high adhesion strength between the substrate and the Ti layer.

When the AlN substrate is a polycrystal, it becomes an epitaxial film corresponding to each grain. There may be a partial non-epitaxial film, as long as at least 50% or more of the area ratio is epitaxially grown.

[0015]

Embodiments will be described below with reference to the drawings. FIG. 1 is a sectional view showing the structure of a circuit board according to an embodiment of the present invention. In the figure, reference numeral 1 denotes an AlN substrate, and an AlTiN layer 2 which is epitaxial with respect to AlN on its surface is provided on this AlN substrate 1. A conductive layer 4 is provided on the AlTiN layer 2 with a Ti layer 3 interposed therebetween.

Here, the epitaxial AlTiN layer 2 is formed.
Means, for example, the following relationship with the AlN substrate 1. That is, at least one of the crystal structure and the plane orientation of the AlTiN layer 2 is the same as that of the AlN substrate 1, and the unidirectional lattice constant of the AlTiN layer 2 is 0.85 or more and 1.15 of that of the AlN substrate 1. Hereafter, it is preferably 0.90 or more and 1.1 or less.

Here, the range of the lattice constant is 0.85 or more and 1.15 or less is less than 0.85 and 1.15.
This is because the lattice mismatch at the interface between the AlN substrate 1 and the AlTiN layer 2 becomes large from the point above.

The composition ratio of Al, Ti and N of the AlTiN layer 2 is determined by the crystal structure and the lattice constant, as long as the adhesion strength between the AlN substrate 1 and the AlTiN layer 2 is not impaired.

According to the circuit board thus configured,
The AlTiN layer 2 that is epitaxial with respect to the AlN on the surface of the AlN substrate 1, in other words, has the same or similar crystal structure, plane orientation, and lattice constant as the AlN substrate 1 is Al.
Since it is provided on the substrate 1, the AlN substrate 1 and the AlT
The defects at the interface with the iN layer 2 are reduced, and the AlN substrate 1
The adhesion strength between AlTiN layer 2 and AlTiN layer 2 is improved.

Further, since the AlTiN layer 2 corresponding to the mutual diffusion layer is provided between the AlN substrate 1 and the Ti layer 3, the AlN substrate 1 is connected to the AlN substrate 1 via the AlTiN layer 2. It comes to firmly adhere.

Next, a method of manufacturing the circuit board shown in FIG. 1 will be described. First, the AlTiN layer 2 is formed on the AlN substrate 1. The AlN substrate 1 has a thermal conductivity of 30 to 310 W.
It is preferably in the range of m ^-1 K ^-1 . This is for the following reason.

Generally, as the thermal conductivity increases, AlN
The sintering aid component contained in the substrate 1 is reduced. When the thermal conductivity is less than 30 Wm ^-1 K ^-1 , the sintering additive component contained in the AlN substrate 1 has a level of several tens at%. The sintering aid component is localized in the crystal grain boundaries of AlN, and the localized area increases as the sintering aid component increases.

Therefore, when the thermal conductivity is less than 30 Wm ^-1 K ^-1 , oxides and nitrides are alternately present on the surface of the AlN substrate 1, and the AlTiN layer 2 is formed. Conditions, adhesion strength, etc. vary greatly, in-plane uniformity deteriorates, and reliability decreases.

On the other hand, if the thermal conductivity exceeds 310 Wm ^-1 K ^-1 , the firing conditions for forming the circuit board are complicated and the number of steps is increased. Furthermore, in the co-fired board often used for circuit boards. The resistance of the inner conductor becomes high, and from these points, Al
Use of the N substrate 1 becomes impractical.

Therefore, the thermal conductivity of the AlN substrate 1 is
As described above, preferably in the range of 30~310Wm ^-1 K ^-1, more preferably, in the range of 40~300Wm ^-1 K ^-1.

As the raw material of the AlTiN layer 2, for example, Al metal, nitride, organic metal and Ti metal, nitride, organic metal or Al and Ti metal, nitride, organic metal, etc. are used. You can The film thickness of the AlTiN layer 2 is about 0.5 to 500 nm.

As a method of forming the AlTiN layer 2, a general film forming technique such as a reactive sputtering method, a vacuum vapor deposition method, a cluster ion beam, an ion plating, an ion mixing, a sol-gel method, etc. is used, and if necessary. , Substrate temperature, atmosphere, degree of vacuum, film formation rate, solution concentration, gas composition, etc. Alternatively, the AlTiN layer 2 may be indirectly formed by forming a metal film of AlTi on the AlN substrate 1 by a thin film method or the like and then nitriding the metal film.

The Ti layer 3 is formed to have a thickness of about 1 to 900 nm. As the material of the conductive layer 4, for example, at least one material selected from Au, Cu, Ag and Al is used. If a thick conductive film 4 having a thickness of several μm or more is required, it may be formed by a plating method or the like.

Further, when forming the AlTiN layer 2, the Ti layer 3 and the conductive layer 4, it is possible to use a lithographic method or a lift-off method. Which method is mainly used is mainly the wiring pitch and the through hole size. It is selected according to the man-hour conditions required for metallization formation.

The etching used for processing the AlTiN layer 2, the Ti layer 3 and the conductive layer 4 may be either wet or dry. In the case of the wet etching method, for example,
A buffer solution of an acid and a salt or an alkali and a salt may be used. On the other hand, in the case of the dry etching method, it may be performed by plasma excitation in a mixture of chlorine, organic chlorine, fluorine, organic fluorine, etc. and argon gas or in argon gas.

In the circuit board of this embodiment, the Ti layer 3 is used.
Is directly in contact with the conductive layer 4, but a barrier layer may be provided between the Ti layer 3 and the conductive layer 4. As the material of the barrier layer, for example, at least one material selected from Ni, Pt, Ta, and W is used.

The present inventors evaluated the circuit board of this embodiment. The type of circuit board is 1 as shown in Table 1.
The number is 0, and the AlTiN layer and the Ti layer were formed by the sputtering method. The parameters are the thermal conductivity of the AlN substrate, the composition of the AlTiN layer, the flow rate ratio of the source gas when forming the AlTiN layer by sputtering, the target power, the substrate temperature and the pressure, the thickness of the Ti layer, and the sputtering of the Ti layer. The target power and pressure when forming, and the material and film thickness of the conductive layer.

[0033]

[Table 1]

The values of the wiring pitch, the wiring width, and the wiring interval are common to all circuit boards and are 5 mm and 2.5 mm, respectively.
mm and 2.5 mm. The circuit board was evaluated as follows. That is, the circuit board is subjected to a thermal cycle of −65 ° C. for 30 minutes to room temperature for 1 minute to 150 ° C. for 30 minutes for 10,000 times.
After repeating the process, as shown in FIG.
(Width 1 mm × thickness 0.2 mm) was joined to the circuit board with solder or brazing material 5, and the peel strength was measured.

As a result, it was confirmed that the peel strength of all the circuit boards was 1000 g or more, the adhesion was excellent, and the reliability was improved. In addition, the sample (No.
1 to 10) were processed by polishing to a thickness of 10 to 100 μm, and then ion milled to prepare a TEM observation sample. The above TEM with an acceleration voltage of 400 keV by TEM
The observation sample was observed, and electron beam diffraction and energy dispersive X-ray diffraction were also performed to determine the orientation, crystal structure, and composition of the interface. The results are shown in Table 2.

[0036]

[Table 2]

From the above evaluation, it was found that the substrate provided with the AlTiN layer had an epitaxial relationship because the crystal orientations of the substrate and the film were the same. On the other hand, AlN substrate and Ti
The same evaluation was performed on a conventional circuit board having no AlTiN layer provided between the layers.

As shown in Table 2, there are five kinds of circuit boards, and the metal layer corresponding to the AlTiN layer (AlTiN equivalent layer) and the Ti layer were formed by the sputtering method. The parameters are the thermal conductivity of the AlN substrate, the material of the AlTiN equivalent layer, the target power when the AlTiN equivalent layer is formed by sputtering, the substrate temperature and pressure, the thickness of the Ti layer, T
The target power and pressure when forming the i layer by sputtering, and the material and film thickness of the conductive layer. The sputter gas when forming the AlTiN equivalent layer by sputtering is Ar gas in any circuit board. The conditions of the wiring pitch, wiring width, and wiring interval of the circuit board are the same as those of the circuit board of the present invention.

[0039]

[Table 3]

In the case of the conventional circuit board, it can be seen from Table 2 that the peel strength value is 50 to 60 g, which is two orders of magnitude smaller than that of the present invention, and the circuit board is inferior in reliability.
Furthermore, TEM observation, electron beam diffraction and energy dispersive X-ray diffraction were performed to examine the orientation, crystal structure, and composition of the interface. In the substrate without the AlTiN layer, there was no specific directional relationship between the substrate and the film. . The interface is Al, Ti,
An amorphous layer containing N was interposed.

[0041]

As described above in detail, according to the present invention, A
Since the AlTiN layer corresponding to the interdiffusion layer of the AlN substrate and the Ti layer is provided between the 1N substrate and the Ti layer and is epitaxial with respect to the AlN substrate, the adhesion and the interface defect are improved, and the circuit board is improved. It is possible to prevent a decrease in reliability due to the.

[Brief description of drawings]

FIG. 1 is a sectional view showing a circuit board according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a circuit board used for evaluation of peel strength.

[Explanation of symbols]

 1 ... AlN substrate 2 ... AlTiN layer (first metal layer) 3 ... Ti layer (second metal layer) 4 ... Conductive layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kaoru Koiwa 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Inside the Toshiba Research and Development Center (72) Inventor Nobuo Iwase Komukai-Toshiba, Kawasaki-shi, Kanagawa Town No. 1 Toshiba Corporation Research & Development Center

Claims (1)

[Claims] 1. A substrate made of aluminum nitride and a first titanium aluminum nitride epitaxially formed on the aluminum nitride on the surface of the substrate.
And a second metal layer made of titanium formed on the first metal layer, and a conductive layer formed on the second metal layer. Circuit board.