JP2000277663A - Composite substrate and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] A composite substrate having high bonding strength and excellent heat-resistant cycle characteristics, and having excellent reliability and durability without causing swelling or peeling of a circuit board even when used for a long time. I will provide a. A circuit board is provided on a surface of a ceramic substrate.
Are integrally bonded to each other, the ratio of the number of carbon atoms to the number of oxygen atoms (O /
C ratio) is 0.9 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite substrate in which a circuit board is integrally joined to a ceramic substrate, and in particular, it can increase the joining strength of the circuit board, prevent swelling and peeling, and reduce the strength decrease due to the deterioration of the joining strength. The present invention relates to a composite substrate which is prevented and has excellent heat cycle characteristics and reliability.

[0002]

2. Description of the Related Art In recent years, as a composite substrate for a power transistor module substrate or a switching power supply module substrate, a composite substrate in which a metal circuit board such as a copper plate is joined to a ceramic substrate has been widely used. Further, instead of the above-mentioned metal circuit board, a composite substrate in which a resin substrate having a metal circuit layer attached thereto is integrally joined to a ceramic substrate surface is also used. In particular, a resin substrate on which a wiring layer pattern or the like can be formed by using photolithography technology has been considered to be promising in order to cope with thinning and narrowing of wiring pitch. In this resin substrate, copper foil for a circuit is bonded to both sides of a resin film such as a liquid crystal polymer, and narrow pitch wiring is enabled for this copper foil by using a photolithography technique.

As the ceramic substrate used for the composite substrate, in addition to an alumina (Al ₂ O ₃ ) substrate, an aluminum nitride substrate, a silicon nitride substrate, and the like, which have an electrical insulating property and an excellent thermal conductivity, are generally used. It is used.

A composite substrate 1 having a circuit board made of a copper plate as described above has, for example, a copper plate as a metal circuit board 3 joined to one surface of a ceramics substrate 2 as shown in FIG. It is formed by joining a copper plate as the back metal plate 4. As a method of integrally forming various circuit boards on the surface of the ceramic substrate 2, the following direct bonding method, refractory metal metallizing method, active metal method, and the like are used. The direct joining method is, for example, a so-called copper direct joining method (DBC method: Direct) in which a copper plate is directly joined on the ceramic substrate 2 using a eutectic liquid phase such as Cu-O.
Bonding Copper method), and the refractory metal metallization method is a method in which a refractory metal such as Mo or W is baked on a ceramic substrate surface to form a circuit layer integrally. In addition, the active metal method uses 4A such as Ti, Zr, and Hf.
This is a method of integrally joining a circuit board on the ceramic substrate 2 via a brazing material layer containing an active metal such as a group element.

Further, as a specific method of forming a circuit,
There are known methods of using a copper plate that has been patterned by press working or etching in advance, and performing patterning by a technique such as etching after bonding. These DB
The composite substrate obtained by the C method or the active metal brazing method
Each of them has an advantage that it has a simple structure, a small thermal resistance, and can cope with a large current type or highly integrated type semiconductor chip.

In recent years, the output of a semiconductor device using a composite substrate and the integration of semiconductor elements have rapidly advanced, and the thermal stress and thermal load repeatedly acting on the composite substrate also tend to increase. However, sufficient bonding strength and durability are required for the above-mentioned thermal stress and thermal cycle.

[0007]

However, in the conventional composite substrate, high bonding strength has been obtained by improving the type of ceramic substrate and the bonding method of the circuit board, but the heat cycle resistance and the bending strength have been improved. There is a problem that the semiconductor device using the composite substrate is not sufficiently obtained, and the reliability and the product yield of the semiconductor device using the composite substrate are lowered.

That is, the thermal cycle load is greatly increased in response to the higher integration and higher output of the semiconductor elements mounted on the composite substrate, and the substrate is cracked due to thermal stress and the function of the composite substrate is lost. There was a problem. Further, in a composite substrate in which a nitride ceramic substrate such as AlN or Si ₃ N ₄ is bonded to a resin substrate via an adhesive, the adhesive strength deteriorates with time in a thermal cycle test. There was a problem. That is,
The adhesive strength between the nitride ceramics substrate and the adhesive was deteriorated by a thermal cycle test, and there was a problem that peeling easily occurred at the interface between the nitride ceramics substrate and the adhesive.

When the peel strength of the circuit board is specifically measured, the following values are obtained. For example, in a composite substrate in which a ceramic substrate and a resin substrate are joined, even if the initial standard value of 1 kg / cm is satisfied, the peel strength after repeating the cooling / heating cycle is 0.3 to 0.3 kg / cm.
It was also found that there was a substance that dropped to 0.7 kg / cm. Further, in the case of a composite substrate in which a ceramic substrate and a copper circuit board are integrally bonded by the direct bonding method (DBC method), even after satisfying the initial standard value of 6 kg / cm, after the thermal cycle test, Peel strength is 3
It was also found that there was a substance which decreased to about 5 kg / cm and caused swelling and peeling. Further, cracks often occur in the ceramic substrate due to thermal stress generated during use, and there has been a problem that the reliability of the semiconductor device using the composite substrate is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has high bonding strength and excellent heat-resistant cycle characteristics without causing swelling or peeling of a circuit board even when used for a long time. An object of the present invention is to provide a composite substrate having excellent reliability and durability.

[0011]

Means for Solving the Problems In order to achieve the above object, the present inventors have made intensive studies, especially for the purpose of preventing the deterioration of the adhesive strength between a ceramic substrate and a circuit board in a thermal cycle test. Was. As a result, it has been found that the presence of a carbon component in the form of a hydrocarbon layer or the like on the surface of the ceramic substrate reduces the bondability between the copper circuit board or the resin substrate and the ceramic substrate. It has also been found that if a certain amount of oxygen atoms exists in the form of an oxide or hydroxide adsorption layer on the surface of the ceramic substrate, the bonding strength between the ceramic substrate and the adhesive does not deteriorate even after a thermal cycle test. Was.

That is, when a copper circuit board and a ceramic substrate are joined by a direct joining method (DBC method),
Oxygen contained in copper is heated to 1065 to 1083 ° C. to form a Cu—O eutectic liquid phase, and the liquid phase is bonded to oxygen in the ceramic substrate, whereby bonding is performed. However, the oxygen required for the reaction is a hydrocarbon (CH
It has been found that the bonding strength between the circuit board and the ceramic substrate decreases due to the carbon component that is consumed by x) or adheres to the surface of the ceramic substrate due to a reaction inhibiting factor at the time of bonding. Then, it was found that when the O / C ratio on the surface of the ceramic substrate was set to 0.9 or more, the bonding strength was significantly increased.

Further, as a treatment for adjusting the O / C ratio to a predetermined range, alkali cleaning or oxygen plasma treatment of the ceramic substrate is extremely effective. If the oxygen plasma treatment is further performed, the oxygen concentration on the substrate surface increases. And
It has also been found that the bonding strength of the composite substrate can be greatly increased by increasing the amount of oxygen contributing to the bonding reaction.

Further, the surface treatment of the ceramic substrate is increased by the alkali treatment or the oxygen plasma treatment for roughening the ceramic substrate, the surface area involved in the bonding is increased, and a good bonding state is obtained. Further, by roughening, the gas mixed at the time of joining is effectively released, and the unjoined portion is reduced. Further, it has been found that the bonding strength of the composite substrate can be improved by the anchor effect of the roughened ceramic substrate surface. This tendency was similarly observed when a resin substrate was integrally joined instead of the metal circuit board.

Further, it has been found that even when a predetermined amount of fluorine (F) atoms is present on the surface of the ceramic substrate, the bonding strength between the ceramic substrate and the circuit board is increased. The present invention has been completed based on the above findings.

That is, the composite substrate according to the present invention is a composite substrate formed by integrally joining a circuit board to the surface of a ceramic substrate. The ratio of the number of atoms (O / C ratio) is 0.9 or more.

Further, the circuit board may be constituted by a metal circuit board, or may be constituted by a resin substrate to which a metal circuit layer is adhered.

Further, it is desirable that the proportion of fluorine atoms present on the surface of the ceramic substrate is 1 at% or more. Further, the metal circuit board may be joined to the ceramic substrate by a direct joining method. Further, the metal circuit board may be a copper circuit board, and the copper circuit board may be joined to the ceramic substrate by a Cu-O eutectic compound.
On the other hand, the circuit board may be configured to be joined to the ceramic substrate via an active metal layer containing at least one selected from Ti, Zr, and Hf. The ceramic substrate is made of at least one of alumina (Al ₂ O ₃ ), aluminum nitride (AlN), and silicon nitride (Si ₃ N ₄ ).

In the method of manufacturing a composite substrate according to the present invention, the surface portion of the ceramic substrate is preliminarily alkali-cleaned to increase the surface roughness, and at the same time, the ratio of the number of carbon atoms to the number of oxygen atoms (O / C
Ratio is adjusted to be 0.9 or more, and thereafter, the circuit board is integrally joined to the surface of the ceramic substrate.

In the above-mentioned manufacturing method, it is preferable to further perform an oxygen plasma treatment after cleaning the surface of the ceramic substrate with an alkali.

That is, in the composite substrate according to the present invention, after performing a surface treatment so as to adjust the O / C ratio on the ceramic substrate surface to 0.9 or more, a circuit board made of metal or resin is integrally joined. Things.

The ceramic substrate used for the composite substrate according to the present invention is not particularly limited. In addition to an oxide ceramic substrate such as aluminum oxide (alumina: Al ₂ O ₃ ), aluminum nitride (Al ₂ O ₃ ) may be used. Al
N), silicon nitride (Si ₃ N ₄ ), titanium nitride (Ti
A non-oxide ceramic substrate such as a nitride such as N), a carbide such as silicon carbide (SiC) or titanium carbide (TiC), or a boride such as lanthanum boride may be used. These ceramic substrates may contain a sintering aid such as yttrium oxide.

In the present invention, the ratio of the number of carbon atoms to the number of oxygen atoms (O / C ratio) on the surface or the surface layer of the ceramic substrate is increased in order to increase the bonding strength between the ceramic substrate and the circuit board and prevent its deterioration. 0.9 or more, preferably 2.0 or more. Examples of a method for making the O / C ratio at the surface of the ceramic substrate 0.9 or more include an alkali cleaning method in which the ceramic substrate is immersed in an alkaline solution, an oxygen plasma treatment method in which the surface of the ceramic substrate is exposed to oxygen plasma, and a ceramic method. There is a method of exposing the substrate to high-temperature steam. In particular, it is more desirable that the ceramics substrate is first subjected to alkali cleaning and then subjected to oxygen plasma treatment. The O / C ratio of the surface of the ceramic substrate was determined by X-ray photoelectron spectroscopy (XPS method).
And the like.

In the above alkaline cleaning treatment and oxygen plasma treatment, the O / C ratio of the surface of the ceramic substrate can be easily adjusted to a predetermined range by increasing or decreasing the treatment time, and the surface of the ceramic substrate is roughened. It is also effective in further increasing the surface roughness and increasing the bonding strength between the ceramic substrate and the circuit board. The roughening of the substrate surface is an operation of roughening the smooth surface roughness of each uneven portion at a minute level of about ± 1 μm, instead of simply increasing the difference in unevenness. Fine roughened state (rough surface) generated by this alkali cleaning treatment or oxygen plasma treatment
As a result, a degassing effect is produced, the unjoined portion is reduced, and the joining strength is further improved by the anchor effect due to the rough surface.

In the above-mentioned oxygen plasma treatment, fluorine can be deposited on the surface of the ceramic substrate by using an oxygen gas containing a small amount of a fluorine gas as an atmosphere gas. 1a on the surface of the ceramic substrate
When fluorine atoms are present at a ratio of tm% or more, the bonding strength between the ceramic substrate and the circuit board can be further improved.

As the metal constituting the circuit board of the composite substrate of the present invention, a eutectic compound with a substrate component such as a simple substance of copper, aluminum, iron, nickel, chromium, silver, molybdenum, cobalt or an alloy thereof is formed. The metal is not particularly limited as long as it is a metal to which the direct bonding method or the active metal method can be applied, but copper, aluminum or an alloy thereof is particularly preferable from the viewpoint of conductivity and cost. Instead of the metal circuit board, a resin substrate to which a metal circuit layer made of the above material is adhered may be integrally joined to the ceramic substrate.

The thickness of the circuit board is determined in consideration of the current carrying capacity and the like.
In the range of 1.2 mm, the thickness of the circuit board is 0.1 to
If both are set in the range of 0.5 mm and they are combined, the influence of deformation or the like due to the difference in thermal expansion is reduced.

In particular, when a copper circuit board is used as a circuit board and bonded to a ceramic substrate by a direct bonding method, a copper circuit board made of tough pitch electrolytic copper containing 100 to 1000 ppm of oxygen is used. By previously forming a copper oxide layer having a predetermined thickness, the amount of Cu—O eutectic generated during direct bonding can be increased, and the bonding strength between the substrate and the copper circuit board can be further improved.

The direct bonding method can be immediately applied to only an oxide-based ceramic substrate such as Al ₂ O ₃ , and can be directly applied to a non-oxide-based ceramic substrate such as aluminum nitride or silicon nitride. Owing to low wettability to the metal circuit board, sufficient bonding strength of the metal circuit board cannot be obtained.

Therefore, when a non-oxide ceramic is used as the ceramic substrate, it is necessary to form an oxide layer on the surface of the non-oxide ceramic substrate in advance to enhance the wettability to the substrate. For example, an oxide layer made of Al ₂ O ₃ or SiO ₂ is formed in advance on an AlN substrate or a Si ₃ N ₄ substrate. The oxide layer is formed by heating the non-oxide ceramic substrate in an oxidizing atmosphere such as air at a temperature of about 1000 to 1400 ° C. for 2 to 15 hours. The thickness of this oxide layer is 0.5 μm
If less than, the effect of improving the wettability is small,
Since the improvement effect is saturated even if the thickness is increased beyond 10 μm, the thickness of the oxide layer needs to be in the range of 0.5 to 10 μm, and more preferably in the range of 1 to 5 μm.

In the composite substrate according to the present invention, the active metal layer formed when the circuit boards are joined by the active metal method contains at least one active metal selected from Ti, Zr, and Hf and contains an appropriate active metal. It is composed of an Ag-Cu-based brazing material having a composition ratio, and is formed by a method such as screen-printing a bonding composition paste prepared by dispersing the brazing material composition in an organic solvent on the surface of a ceramic substrate. .

The following are specific examples of the bonding composition paste. That is, a composition consisting of 15 to 35% by weight of Cu, 1 to 10% of at least one active metal selected from Ti, Zr, and Hf and a balance substantially composed of Ag is dispersed in an organic solvent. It is good to use the bonding composition paste prepared in this way.

The active metal is a component for improving the wettability of the brazing material to the ceramic substrate, and is particularly effective for an aluminum nitride (AlN) substrate. The amount of the above active metal is 1 to 1 with respect to the whole bonding composition.
10% by weight is an appropriate amount.

According to the composite substrate and the method of manufacturing the same according to the above configuration, the ratio of the number of carbon atoms to the number of oxygen atoms (O / C ratio) at the surface of the ceramic substrate is 0.9 or more. The bonding strength with the circuit board is increased, and the bonding strength is not deteriorated even after the thermal cycling test, the swelling or peeling of the circuit board is small, and a composite substrate excellent in reliability and durability can be obtained.

Further, the above-mentioned O / C ratio is adjusted to a predetermined range by alkali washing or oxygen plasma treatment of the ceramic substrate, and the surface of the ceramic substrate is roughened. Can further increase the bonding strength. Furthermore, by roughening, the escape of gas generated at the time of joining becomes better, and the occurrence of unjoined portions due to gas stagnation is reduced. In addition, the presence of 1 at% or more of fluorine atoms on the surface of the ceramic substrate makes it possible to further increase the bonding strength between the ceramic substrate and the circuit board.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described more specifically with reference to the accompanying drawings based on the following embodiments.

FIG. 1 is a sectional view showing a structure of a composite substrate according to the present invention in which circuit boards are joined by a direct joining method (DBC method). This composite substrate 1a has an oxide layer (Al ₂ O ₃ film) on the surface of an AlN substrate as a ceramic substrate 2a.
After the formation of 5, the copper circuit board 3 is joined to the front side of the AlN substrate 2a, and the back copper sheet 4 is joined to the back side.

The detailed manufacturing process of the composite substrate 1a is as follows. That is, 5% by weight of Y ₂ O ₃ powder as a sintering aid was added to Al ₂ O with respect to aluminum nitride powder.
₃ powders and 3% by weight were added and mixed to prepare a raw material mixture. A binder and a solvent were added to the raw material mixture to prepare a raw material slurry. Further, the raw material slurry was formed into a sheet having a thickness of 0.8 mm by a doctor blade method, and cut into pieces having a size after sintering of 50 mm long × 25 mm wide to prepare a large number of sheet-shaped formed bodies. Next, the powder was heated to a temperature of 500 ° C. and degreased in a state in which the bedding powder composed of boron nitride (BN) was arranged on the surface of the molded body. Next, each degreased body was sintered at a temperature of 1750 ° C. for 4 hours in a non-oxidizing atmosphere to prepare an AlN substrate. Next, the surface of each AlN substrate was cleaned to obtain an AlN substrate in which a compound serving as a liquid phase component was distributed by a predetermined amount on the substrate surface.

Next, each of the obtained AlN substrates is housed in a heating furnace adjusted to an air atmosphere, and heated at a temperature of 1300 ° C. for 12 hours to oxidize the entire surface of the AlN substrate.
An oxide layer (Al ₂ O ₃ film) 5 having a thickness of 2 μm as shown in FIG. 1 was formed.

Next, the following surface treatment was performed on each AlN substrate 2a on which the oxide layer 5 was formed as described above to prepare an AlN substrate for each embodiment.

Example 1 An AlN substrate was immersed in a 25% caustic soda solution heated to a temperature of 20 to 40 ° C. and subjected to ultrasonic cleaning for 50 minutes to obtain an AlN substrate for Example 1. .

Example 2 An AlN substrate was placed in an oxygen ashing apparatus adjusted to a pressure of 30 Pa, an oxygen flow rate of 100 SCCM, and an input power of 400 W, and subjected to oxygen plasma treatment in which the AlN substrate surface was exposed to oxygen plasma for 120 seconds. The AlN substrate for Example 2 was used.

Example 3 An AlN substrate was immersed in a 25% caustic soda solution heated to a temperature of 20 to 40 ° C., subjected to an ultrasonic cleaning for 50 minutes, and further subjected to a pressure of 30 Pa and an oxygen flow rate. The AlN substrate was placed in an oxygen ashing apparatus adjusted to 100 SCCM and the input power to 400 W, and subjected to oxygen plasma treatment for exposing the AlN substrate surface to oxygen plasma for 60 seconds to obtain an AlN substrate for Example 3.

[0044] Comparative Example 1 oxide layer (Al ₂ O ₃ film) 5 only is formed, without performing the alkali cleaning treatment and oxygen plasma treatment, as the AlN substrate for Comparative Example 1.

The C / O ratio of each of the AlN substrates for Examples 1 to 3 and Comparative Example 1 obtained as described above was measured by XPS (X-ray photoelectron spectroscopy), and the results shown in Table 1 were obtained. Obtained.

Next, a copper circuit board as a metal circuit board made of tough pitch electrolytic copper having a thickness of 0.25 mm containing oxygen is arranged in contact with the front side of each AlN substrate on which the oxide layer is formed, while the back side is disposed. A copper plate as a back metal plate made of tough pitch copper having a thickness of 0.25 mm was placed in contact with the substrate to form a laminate.
By inserting into a heating furnace set at 5 ° C. and heating for 1 minute, a joined body in which a metal circuit board (Cu board) or a back copper board is directly joined to both sides of each AlN substrate by a direct joining method (DBC method) is prepared. did. Further, each of the joined bodies was subjected to an etching treatment to prepare ten composite substrates according to each of the examples and the comparative examples each having a predetermined circuit pattern as shown in FIG.

With respect to the thus prepared DBC composite substrates according to Examples and Comparative Examples, in order to evaluate the bonding strength of the circuit boards, each circuit board was peeled off in a direction perpendicular to the substrate, and the peel strength was measured. The results shown in Table 1 were obtained.

[0048]

[Table 1]

As is clear from the results shown in Table 1 above,
In the composite substrate of each of the examples, in which the surface of the ceramic substrate was previously subjected to alkali cleaning or oxygen plasma treatment to make the O / C ratio equal to or higher than a predetermined value, the peel strength was lower than that of Comparative Example 1 in which the above treatment was not performed. And a composite substrate excellent in bonding strength and durability was obtained.

In the above embodiment, an example is shown in which an AlN substrate is used as the ceramic substrate.
It has been confirmed that a composite substrate having high peel strength can be obtained by similarly performing alkali cleaning and oxygen plasma treatment on the Al ₂ O ₃ substrate and the Si ₃ N ₄ substrate.

Next, an embodiment of a composite substrate (resin composite substrate) using a resin substrate as a circuit board will be described.

A large number of silicon nitride (Si ₃ N ₄ ) substrate materials having a surface roughness (Rmax) of 10 μm and an O / C ratio of the surface portion of 0.5 are prepared, and each of the Si ₃ N ₄ substrates has the following properties. By performing such a surface treatment, a Si ₃ N ₄ substrate for each example was prepared.

Example 4 The above-mentioned Si ₃ N ₄ substrate material was subjected to the alkali cleaning treatment shown in Example 1 for 50 minutes to obtain Si ₃ N ₄ for Example _4.
A substrate was prepared.

Embodiment 5 The above-mentioned Si ₃ N ₄ substrate material was subjected to the oxygen plasma treatment shown in Embodiment 2 for 120 seconds to perform Si ₃ N for Embodiment 5.
_Four substrates were prepared.

Example 6 The above-described Si ₃ N ₄ substrate material was subjected to the alkali cleaning treatment shown in Example 1 for 50 minutes, and then to the oxygen plasma treatment shown in Example 2 for 60 seconds. A Si ₃ N ₄ substrate was prepared.

Example 7 The above-mentioned Si ₃ N ₄ substrate material was subjected to the alkali cleaning treatment shown in Example 1 for 50 minutes, and further subjected to the oxygen plasma treatment shown in Example 2 for 120 seconds. A Si ₃ N ₄ substrate was prepared.

[0057] without any implementing Comparative Example 2 alkali cleaning treatment and oxygen plasma treatment, and the _Si 3 _{N 4} substrate of the _Si 3 _{N 4} substrate material as it is for comparative example 2.

COMPARATIVE EXAMPLE 3 The above-mentioned Si ₃ N ₄ substrate material was subjected to the oxygen plasma treatment shown in Example 2 for 15 seconds to obtain Si ₃ N ₄ for Comparative Example 3.
A substrate was prepared.

The surface roughness of the Si ₃ N ₄ substrates for each of the examples and comparative examples prepared as described above was measured, and
The O / C ratio of the substrate surface was measured by the XPS method, and the results shown in Table 2 were obtained.

On the other hand, a resin substrate for bonding to each of the above Si ₃ N ₄ substrates was prepared as follows. That is, a copper foil was bonded to both sides of a resin film composed of a liquid crystal polymer, and a wiring layer pattern such as a chip mounting portion and a wiring portion was formed on the copper foil by photolithography technology, thereby preparing a large number of resin substrates. .

Then, each of the Si ₃ N ₄ prepared as described above is used.
By bonding the above resin substrates integrally to the surface of the substrate using an epoxy resin adhesive, ten composite substrates (resin composite substrates) according to Examples 4 to 7 and Comparative Examples 2 to 3, respectively. Prepared.

With respect to each of the resin composite substrates according to the examples and the comparative examples thus prepared, the bonding strength was calculated from the value measured by the peel test. Specifically, the test was performed in accordance with a 90-degree peel test in which a copper foil of a resin substrate was bent in the vertical direction and pulled in the vertical direction. The peel test was performed before and after a thermal cycle test (TCT) in which the thermal cycle of 125 ° C. on the high temperature side and −40 ° C. on the low temperature side was repeated up to 800 cycles for each composite substrate. The measurement results are shown in Table 2 below. Table 2 shows the O / C ratio and surface roughness (Rma) of the ceramic substrate surface of each composite substrate.
x) is also shown.

[0063]

[Table 2]

As is clear from the results shown in Table 2 above,
In each comparative example, although the adhesive strength in the initial state (before the thermal cycle test) is a sufficient value of 1.3 to 1.4 kgf / cm, the adhesive strength is increased to 0.2 kgf / cm after the thermal cycle test of 800 cycles. It turns out that it deteriorates even to. On the other hand, in each of the examples, it was found that the adhesive strength hardly deteriorated under all the conditions. Therefore, from this result, by subjecting the nitride ceramics substrate to the above-described alkali cleaning treatment or the like, the atomic ratio of oxygen to nitrogen on the substrate surface or the surface layer becomes larger than 0.9, thereby increasing the cooling / heating cycle. It was demonstrated that the deterioration of the adhesive strength before and after the test was suppressed.

The surface roughness (Rmax) is 10 μm, the surface has an oxide layer (Al ₂ O ₃ film), and the surface has an O / C
The aluminum nitride according to Comparative Example 1 having a ratio of 0.5 (A
1N) A number of substrate materials were prepared, and each AlN substrate was subjected to the following surface treatment to prepare an AlN substrate for each example.

Example 8 The AlN substrate material was subjected to the alkali cleaning treatment shown in Example 1 for 30 to 120 minutes, and the O / C shown in Table 3 was obtained.
AlN substrates for Example 8 having the following were prepared.

Example 9 The AlN substrate material was subjected to the oxygen plasma treatment shown in Example 2 for 150 to 300 seconds to prepare AlN substrates for Example 9 having O / C shown in Table 3 respectively. .

Example 10 The AlN substrate material was subjected to the alkali cleaning treatment shown in Example 1 for 50 to 90 minutes, and further subjected to the oxygen plasma treatment shown in Example 2 for 60 to 150 seconds. AlN for Example 10 having O / C shown in
Substrates were prepared respectively.

Next, a copper circuit board as a metal circuit board made of tough pitch electrolytic copper having a thickness of 0.25 mm containing oxygen was placed in contact with the front side of each AlN substrate, while the thickness of the copper circuit board was 0.25 mm on the back side. A copper plate as a back metal plate made of tough pitch copper was placed in contact with the laminate to form a laminate, and the laminate was adjusted to a nitrogen gas atmosphere, inserted into a belt furnace set at a temperature of 1070 ° C., and heated for 1 minute. Bonded bodies in which a metal circuit board (Cu board) or a back copper board was bonded to both surfaces of each AlN substrate by a direct bonding method (DBC method) were prepared. Further, each of the joined bodies was subjected to an etching treatment to prepare ten composite substrates according to each of the examples and the comparative examples each having a predetermined circuit pattern as shown in FIG.

With respect to the thus prepared DBC composite substrates according to Examples and Comparative Examples, in order to evaluate the bonding strength of the circuit boards, each circuit board was peeled off in a direction perpendicular to the substrate, and the peel strength was measured. The results shown in Table 3 were obtained.

[0071]

[Table 3]

As is clear from the results shown in Table 3 above,
In each of the embodiments in which the surface of the ceramic substrate was previously subjected to alkali cleaning or oxygen plasma treatment to make the O / C ratio equal to or higher than a predetermined value, compared to Comparative Example 1 in which the above treatment was not performed,
In each case, a composite substrate having high peel strength and excellent bonding strength and durability was obtained.

Next, the effect of the amount of fluorine on the surface of the ceramic substrate on the bonding strength will be described with reference to the following examples.

Comparative Example 4 and Examples 12 to 14 An AlN substrate having an O / C ratio of 0.7 on the substrate surface was prepared as a ceramic substrate for Comparative Example 4. On the other hand, the AlN substrate prepared in Comparative Example 1 was subjected to oxygen plasma treatment for 120 seconds and 180 seconds, respectively, under the same conditions as the process shown in Example 2 except that an oxygen gas containing a small amount (150 ppm) of fluorine gas was used. As a result, as shown in Table 4, the AlN for Examples 12 and 14 in which the O / C ratio on the substrate surface is 0.9 and 2.0 was obtained.
A substrate was prepared. Further, the AlN substrate prepared in Comparative Example 1 was subjected to an alkali cleaning treatment for 70 minutes under the same conditions as in the process shown in Example 1, so that the O / C ratio on the substrate surface was 2. An AlN substrate for Example 13, which was 0, was prepared.

For each of the AlN substrates thus prepared, the fluorine (F) atom abundance on the surface was measured by the XPS method.
The results shown in Table 4 were obtained. Further, a copper circuit board and a back copper plate were integrally bonded to each AlN substrate by a direct bonding method (DBC method) in the same manner as in Example 1 to obtain composite substrates according to Comparative Example 4 and Examples 12 to 14, respectively. Each was prepared. The bonding strength of the copper circuit board for each composite substrate was measured by a peel test, and the results shown in Table 4 below were obtained.

[0076]

[Table 4]

As is clear from the results shown in Table 4 above,
Example 1 in which the O / C ratio of the ceramic substrate surface is the same
It has been found that the bonding strength of the circuit board changes greatly depending on the amount of fluorine (F) deposited on the substrate surface even with the composite substrates of Nos. 3 to 14, and when the fluorine amount is 1 at% or more, the bonding strength significantly increases. It was confirmed that it was improved.

The amount of the fluorine (F) atom is as follows:
When the circuit board is joined to the ceramic substrate by the direct joining method (DBC method) as in the above Examples 12 to 14, it worked in a direction to improve the joining strength, but the resin substrate and the ceramic substrate were bonded with an adhesive. It has been confirmed that the bonding strength is rather lowered when bonding is performed by using the method described above.

Next, a method of joining metal circuit boards (DBC method,
The influence of the difference of the active metal method) on the substrate characteristics such as bonding strength will be described based on the following examples.

Examples 15 to 17 As shown in Table 5, the AlN substrate material having an O / C ratio of 0.5 on the substrate surface was subjected to the alkali cleaning treatment performed in Example 1 and the alkali cleaning treatment performed in Example 2. By performing at least one of the oxygen plasma treatments, O / O
AlN substrates for Examples 15 to 17 each having a C ratio of 2.0 and an F amount of 3.4 atm% were prepared.

For the AlN substrates for Examples 15 and 16, a copper circuit board was integrally joined by the DBC method as in Example 1 to prepare composite substrates according to Examples 15 and 16, respectively.

On the other hand, a powder mixture 100 containing 3% of Ti powder, 27% of Ag powder and 70% of Cu powder by weight ratio.
20 parts by weight of a binder solution obtained by dissolving ethyl cellulose as a binder in terpineol as a solvent is added to parts by weight, mixed with a mortar, and kneaded with a three-stage roll to form a paste-like bonding composition. Prepared.

Then, a metal circuit board and a back metal plate were disposed in contact with each other on both surfaces of the aluminum nitride (AlN) substrate for Example 17 with the paste-like bonding composition interposed therebetween, thereby forming a three-layer laminate. Each of the laminates was placed in a heating furnace, the inside of the furnace was adjusted to a degree of vacuum of 1.3 × 10 ⁻⁸ MPa, and then heated at a temperature of 850 ° C. for 15 minutes to form an AlN film as shown in FIG. The metal circuit board 3 and the back metal plate 4 were integrally joined to the substrate 2a to obtain a large number of joined bodies. Then, an etching process was performed on each bonded body to obtain a composite substrate according to Example 17 having a predetermined circuit pattern.

For the composite substrates according to Examples 15 to 17 prepared as described above, the bonding strength of the circuit board was measured by a peel test, and the undulation (warpage) of the composite substrate after the composite was measured. The results shown in FIG.

[0085]

[Table 5]

As is clear from the results shown in Table 5 above,
Even when the circuit board was bonded to the substrate by the DBC method or the active metal method, there was no significant difference between the two.

[0087]

As described above, according to the composite substrate and the method of manufacturing the same according to the present invention, the ratio of the number of carbon atoms to the number of oxygen atoms on the surface of the ceramic substrate (O / C ratio)
Is 0.9 or more, the bonding strength between the ceramic substrate and the circuit board is increased, and the bonding strength does not deteriorate even after the thermal cycle test, and the circuit board does not swell or peel off, and the reliability is improved. And a composite substrate having excellent durability can be obtained.

Also, by cleaning the ceramic substrate with an alkali or oxygen plasma treatment, the O / C ratio is adjusted to a predetermined range and the surface of the ceramic substrate is roughened. Can further increase the bonding strength. Furthermore, by roughening, the escape of gas generated at the time of joining becomes better, and the occurrence of unjoined portions due to gas stagnation is reduced. In addition, the presence of 1 at% or more of fluorine atoms on the surface of the ceramic substrate makes it possible to further increase the bonding strength between the ceramic substrate and the circuit board.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of a composite substrate according to the present invention.

FIG. 2 is a cross-sectional view illustrating a structural example of a composite substrate.

[Explanation of symbols]

1,1a Composite substrate 2,2a Ceramic substrate (AlN substrate, Si ₃ N ₄
Substrate) 3 Circuit board (metal circuit board, copper circuit board, resin substrate) 4 Back metal plate (back copper plate) 5 Oxide layer (Al ₂ O ₃ layer)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 1/03 610 H05K 1/09 C 1/09 3/20 Z 3/20 H01L 23/12 C F term (Ref.) BB67 CC43 DD56 EE02 EE37 GG02

Claims (10)

[Claims] In a composite substrate formed by integrally joining a circuit board to the surface of a ceramic substrate, the ratio of the number of carbon atoms to the number of oxygen atoms (O / C) on the surface of the ceramic substrate which is the joining surface of the circuit board Ratio) is 0.9 or more. 2. The composite board according to claim 1, wherein the circuit board is a metal circuit board. 3. The composite board according to claim 1, wherein the circuit board is a resin board to which a metal circuit layer is attached. 4. The composite substrate according to claim 1, wherein the proportion of fluorine atoms on the surface of the ceramic substrate is 1 at% or more. 5. The composite substrate according to claim 2, wherein the metal circuit board is bonded to the ceramic substrate by a direct bonding method. 6. The composite substrate according to claim 2, wherein the metal circuit board is a copper circuit board, and the copper circuit board is joined to the ceramic substrate by a Cu—O eutectic compound. 7. The composite substrate according to claim 1, wherein the circuit board is joined to the ceramic substrate via an active metal layer containing at least one selected from Ti, Zr, and Hf. 8. The ceramic substrate is made of alumina (Al ₂ O).
₃ ), aluminum nitride (AlN), silicon nitride (Si
_3. The composite substrate according to claim 1, wherein the composite substrate comprises at least one of 3N ₄ ). 9. The surface roughness of the surface of the ceramic substrate is increased by previously washing the surface of the ceramic substrate with an alkali, and the ratio of the number of carbon atoms to the number of oxygen atoms (O / C ratio) on the surface of the ceramic substrate is 0.9 or more. A method of manufacturing a composite substrate, comprising: adjusting a circuit board so that the circuit board is integrally formed on the surface of the ceramic substrate. 10. The method for manufacturing a composite substrate according to claim 9, wherein an oxygen plasma treatment is further performed after the surface of the ceramic substrate is washed with alkali.