JP2002076192A - Aluminum nitride board and semiconductor package using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum nitride board or a semiconductor package preventing the swelling of a metallized layer and preventing the jetting of nitrogen gas during sealing. SOLUTION: In the aluminum nitride board providing an oxide film on the whole face, particle growth more than the need of metal particles constituting the metallized layer is prevented by making the film thickness of an oxide film existing on a part providing the metallized layer 0.3-2 μm and making a difference between the maximum value and the minimum value of the film thickness 0.2 μm or less. Thereby the swelling of the metallized layer can be suppressed. In addition, the jetting of nitrogen gas can be suppressed by providing the similar oxide film on the sealing part of the package.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride substrate and a semiconductor package using the same.

[0002]

2. Description of the Related Art The power consumption of semiconductor devices has increased with the increase in integration, density, and speed of semiconductor devices, and heat generation of the semiconductor devices has become a problem. In order to solve the problem of heat generation, ceramic substrates such as aluminum nitride have been used as substrates on which semiconductor elements are mounted. The aluminum nitride substrate has an excellent thermal conductivity of 150 W / m · k or more, and thus has good heat dissipation.
In recent years, this heat dissipation property has been utilized for various electronic circuit boards and semiconductor packages such as a board for a high-power power module and a package for a supercomputer. When forming an electronic circuit board or a semiconductor package, a metallized layer such as a brazing material is provided on an aluminum nitride substrate, and a semiconductor element is brazed thereon or joined by a conductive adhesive. At this time, if the metallized layer is provided directly on the aluminum nitride substrate, if the wettability between the metallized layer and the brazing material is poor, the metallized layer is adversely affected and causes problems such as blistering. In addition, when used as a semiconductor package, the lead frame and the cap are sealed with a glass-based sealing material. However, heat treatment during sealing decomposes aluminum nitride and spouts nitrogen gas to deteriorate airtightness. There was a problem such as causing

In order to solve such a problem, an oxide film is conventionally provided on an aluminum nitride substrate.

[0004]

However, in the conventional aluminum nitride substrate provided with an oxide film, attention has been paid only to the provision of the oxide film, so that the thickness of the oxide film varies. If the thickness of the oxide film varies, thick portions and thin portions of the oxide film exist, and the heat transmission during brazing varies. If the distribution of heat to the metallized layer varies, the metal particles in the brazing material, which is the metallized layer, do not dissolve uniformly, and in particular, the metal particles that have entered the concave portions of the oxide film do not dissolve uniformly. It has been found that the metal particles grown by the grain formation cause a slight gap between the metal film and the oxide film. It has been found that such voids accompanying the growth of metal particles constituting the metallized layer not only reduce the bonding strength of the metallized layer but also cause blisters. To solve such a problem, it is conceivable to increase the thickness of the oxide film. However, since the oxide film is not so good in heat conductivity, if the oxide film is too thick, it becomes a thermal resistance. You can't take advantage of good conductivity. Further, if the oxide film is too thick, the oxide film itself undergoes thermal expansion due to various heat treatments, and this thermal expansion has caused a problem with the metallized layer and the like.

Similarly, when the semiconductor package is sealed with a glass-based sealing material, if the thickness of the oxide film varies, nitrogen gas is likely to be ejected only from the thin portion of the oxide film, resulting in unnecessary stress concentration. Will occur. In addition, nitrogen gas is ejected from other than the sealing part,
The jetted nitrogen gas may adversely affect the sealing portion. Unnecessary stress concentration due to such unevenness in the thickness of the oxide film is caused by forming a metallized layer that is difficult to judge from the external appearance, brazing the semiconductor element, sealing the lead frame, or moving the semiconductor element. It can be understood only when a problem such as film peeling occurs from a difference in thermal expansion between aluminum nitride and a metallized layer, a lead frame, and a glass-based sealing material. Similarly, the portion where the oxide film is thick has a high thermal resistance only at that portion, and further results in further increase in film peeling and blistering due to the above-mentioned thermal expansion. The present invention has been made in order to solve the above problem, and in a substrate having an oxide film provided on the entire surface of an aluminum nitride substrate, the difference between the maximum value and the minimum value of the oxide film thickness is small.
By using a uniform oxide film having a thickness of 0.2 μm or less, an aluminum nitride substrate was used which reduced defects such as blistering of the metallized layer due to ejection of a liquid phase component and film peeling due to a difference in thermal expansion between the lead frame and the like. It is an object to provide a semiconductor package.

[0006]

The aluminum nitride substrate of the present invention has an oxide film provided on the entire surface of the substrate. In particular, the thickness of the oxide film where the metallized layer is provided is 0.3 μm or more and 2 μm or less, and Wherein the difference between the maximum value and the minimum value is 0.2 μm or less. Preferably, the oxide film contains aluminum oxide as a main component.

Further, the surface roughness Ra of the aluminum nitride substrate before the oxide film is provided is 0.8 μm or less, or the surface roughness Rma
x is preferably 6 μm or less. Such an aluminum nitride substrate of the present invention is preferably used in a form in which a metallized layer is provided on at least a part of the oxide film.
When the metallized layer is formed, virtually no blisters having a maximum diameter of 0.2 mm or more exist in the metallized layer.

Similarly, the semiconductor package of the present invention uses an aluminum nitride substrate having an oxide film provided on the entire surface of the aluminum nitride substrate, and the thickness of the oxide film existing at a location sealed by the metallization layer and the sealing material is reduced. 0.3μm or more and 2μm
And the difference between the maximum value and the minimum value of the film thickness is 0.2 μm or less. In addition, the lead frame was joined by a glass-based sealing material, and the semiconductor package was QFP.
In the case of a QFP type semiconductor package, the number of inputs and outputs by a lead frame is preferably 120 or more.

In the aluminum nitride substrate of the present invention, an oxide film is provided on the entire surface of the substrate, and the thickness of the oxide film existing at the place where the metallized layer is provided or at the place where the oxide film is sealed by the sealing material.
By providing a uniform oxide film with a thickness of 0.3 to 2 μm and a difference between the maximum value and the minimum value of the film thickness of 0.2 μm or less, problems such as blistering of the metallized layer and ejection of nitrogen gas are reduced, and reliable aluminum nitride This realizes a substrate or a semiconductor package.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of an aluminum nitride substrate and a semiconductor package using the same according to the present invention will be described. The aluminum nitride substrate of the present invention has an oxide film provided on the entire surface as shown in FIG. 1, for example. In FIG. 1, 1 is an aluminum nitride substrate, 2 is an oxide film,
Reference numeral 3 denotes a metallized layer. If the oxide film is formed only partially, for example, only on the surface on which the metallized layer is formed, it becomes impossible to suppress blistering or nitrogen gas jetting caused by heat treatment at the time of forming the metallized layer or brazing the semiconductor element.

It is also considered that a difference in the coefficient of thermal expansion between a portion where the oxide film exists and a portion where the oxide film does not exist is a cause of defects such as blisters. Therefore, it is preferable that the oxide film is provided on the entire surface of the aluminum nitride substrate. The average thickness of the oxide film existing at the place sealed by the metallized layer or the sealing material is 0.3 μm or more and 2 μm or less. Oxide film thickness of 0.3
If it is less than μm, the effect of providing an oxide film is small because the film thickness is too thin, and problems such as ejection of nitrogen gas are likely to occur.
On the other hand, when the thickness of the oxide film is more than 2 μm, the ejection of nitrogen gas can be suppressed, but the thermal resistance of the oxide film is lower than that of aluminum nitride, so that the thermal resistance of the substrate (or semiconductor package) becomes poor. As a result, good heat dissipation of aluminum nitride cannot be achieved. Further, since the oxide film itself thermally expands during various heat treatments, it is not preferable that the thickness of the oxide film exceeds 2 μm. Therefore, the thickness of the oxide film is 0.3 μm or more and 2 μm or less, preferably
It is 0.5 μm or more and 1.5 μm or less.

In the present invention, the portion having a predetermined oxide film thickness is a portion where a metallized layer is provided on an aluminum nitride substrate, a portion where a metallized layer is provided and a portion where a metallized layer is sealed with a sealing material in a semiconductor package. An oxide film is provided on the entire aluminum nitride substrate of the present invention, and the other portions have an average film thickness of 0.
It is preferable that the thickness be in the range of 3 μm or more and 2 μm or less. Similarly, the difference between the maximum value and the minimum value of the thickness of the oxide film other than the metallized layer and the portion to be sealed is preferably 0.2 μm or less.

The method of measuring the thickness of the oxide film and the difference between the maximum value and the minimum value is based on the difference between the weight of the aluminum nitride substrate before the oxide film is provided and the weight of the aluminum nitride substrate after the oxide film is provided. (The weight difference substantially indicates the weight of the oxide film.)
Is effective in obtaining an average film thickness from the substrate. This method is particularly effective for a substrate provided with an aluminum oxide film by heating an aluminum nitride substrate in an oxidizing atmosphere.

In another method, a method of analyzing a cross section of an aluminum nitride substrate provided with an oxide film by FESEM or the like is effective. At the time of analysis, there is no problem as long as all the portions where the metallized layer is formed can be analyzed, but in a simple manner, three arbitrary lengths are measured in a range of 200 μm or more, preferably 2000 μm, and the average value is used. May be used. In forming the cross section, it is preferable to cut and cut the surface opposite to the surface on which the metallization is formed, because the form of the oxide film existing at the position where the metallization layer is provided does not need to be changed.

Further, the method using FESEM or the like can be used for measuring the difference between the maximum value and the minimum value of the oxide film since an enlarged photograph is used. Further, a measurement method for measuring the thickness of the oxide film at the position where the sealing portion of the semiconductor package described later is provided and the difference between the maximum value and the minimum value of the oxide film thickness can be handled by the same method.

The material of the oxide film is not particularly limited as long as it is an oxide, but is preferably aluminum oxide. As the material of the oxide film, aluminum oxide,
Various oxides or composite oxides such as silicon oxide, magnesium oxide, and copper oxide can be used. However, aluminum oxide can be formed by heating an aluminum nitride substrate in an oxidizing atmosphere as described later, so that it is inexpensive. Can be manufactured. In the case of other oxides, a step of applying a compound which becomes an oxide by a heat treatment such as a paste or an alkoxide containing the oxide is required, and the productivity is not necessarily good. Similarly, the sputtering method and CV
Although it is possible to provide an oxide film by the method D, all of them require a high manufacturing cost and cannot always be said to have good productivity. Therefore, in consideration of manufacturability, the oxide film is preferably made of aluminum oxide.

In the present invention, such a difference between the maximum value and the minimum value of the oxide film thickness is suppressed to 0.2 μm or less. When the maximum value and the minimum value of the oxide film thickness exceed 0.2 μm, irregularities are formed more than necessary on the oxide film, and particularly, the metal particles forming the metallized layer enter the recesses and enter the recesses during heat treatment. When the metal particles grow independently of the other metal particles without being dissolved, voids are formed between the oxide film and the metallized layer, causing blisters. Unnecessary stress concentration due to the difference in thermal expansion between the oxide film and aluminum nitride, or the difference in thermal expansion between the oxide film itself due to the difference in thermal resistance between the thick and thin portions of the oxide film, and the ejection of nitrogen gas Unnecessary stress concentration is likely to occur in a portion having a small oxide film thickness. Therefore, the maximum and minimum values of the oxide film thickness are 0.2 μm or less, preferably 0.1 μm or less.

In view of the concept of relieving grain growth and unnecessary stress concentration of the metal particles forming the metallized layer, if the parts exhibiting the maximum and minimum values of the oxide film thickness are too close to each other, the oxidation may occur. This is not a preferable mode because a steep valley is formed in the cross-sectional shape of the film. Therefore, the region showing the maximum and minimum values of the oxide film thickness is 200
It is preferable that the shape be spaced apart by at least μm, more preferably at least 1000 μm.

As a method of measuring the maximum value and the minimum value of the oxide film, there is no particular problem if the metal oxide layer (or the sealing portion) of the aluminum nitride substrate (or semiconductor package) where the metallized layer (or the sealing portion) is provided can be measured. No,
For simplicity, a method of examining three arbitrary cross sections of 2000 μm may be used.

The aluminum nitride substrate of the present invention is characterized in that an oxide film having a uniform thickness is provided. In order to keep the oxide film thickness uniform, it is preferable that the surface roughness of the aluminum nitride substrate is also uniform.
Preferably, it is 0.8 μm or less, and Rmax is 6 μm or less.
If Ra exceeds 0.8 μm or Rmax exceeds 6 μm, it is difficult to make the difference between the maximum value and the minimum value of the oxide film less than 0.2 μm unless the average thickness of the oxide film exceeds 2 μm. When the metallized layer is provided on the aluminum nitride substrate of the present invention in which the difference between the maximum value and the minimum value of the oxide film thickness is 0.2 μm or less, blisters having a maximum diameter of 0.2 mm or more are not substantially generated in the metalized layer. Will be.

Ag, Cu, W, Mo, Au, T
A paste or foil in which at least one or two or more of i, Hf, Zr, Pt, and Pb are mixed and laminated may be used.
The thickness of the metallized layer is preferably in the range of 10 to 30 μm,
If it is less than μm, the bonding strength as a metallized layer cannot be maintained, and furthermore blisters are likely to occur. On the other hand, even if the thickness is more than 30 μm, the effect is only saturated, and the thickness is preferably in the range of 10 to 20 μm.

The blister means that a convex portion is formed on the metallized layer in appearance, and the presence of such blister causes a bonding failure when bonding a semiconductor element, a metal circuit board, a lead frame, and the like. . In particular, blisters with a maximum diameter of 0.2 mm or more tend to cause poor bonding,
By controlling the difference between the maximum value and the minimum value of the oxide film thickness to 0.2 μm or less, blisters having a maximum diameter of 0.2 mm or more can be substantially eliminated. Further, when observed microscopically, the number of blisters having a maximum diameter of less than 200 μm (0.2 mm) in the metallized layer, and further, a maximum diameter of 20 μm or less can be suppressed to 0 to 2 or less in a unit area of 20 mm × 20 mm. The maximum diameter of the blister indicates the longest diagonal line of each blister by observing the upper surface or the cross section of the metallized layer.

The above-described oxide film or the aluminum nitride substrate provided with the metallized layer on the oxide film is suitable for a semiconductor package. Semiconductor packages include, for example, DIP (dial inline package) using a lead frame, QFP (quad flat package), PGA (pin grid array) using lead pins, and lead pins as described in JP-A-7-202109. BGA (ball grid array) having a ball-like shape, LGA (land grid array) using input / output lands, and the like are known. For example, a package structure using a lead frame has been applied to various semiconductor chips because of its simple structure. Particularly, a QFP type semiconductor package can cope with an increase in the number of input / output signals and can be surface-mounted. This is a preferred form. The aluminum nitride substrate of the present invention is applicable to such various packages.

For example, FIG. 2 shows an example of a sectional view of a QFP type package. In FIG. 2, 1 is an aluminum nitride substrate,
2 denotes an oxide film, 3 denotes a metallized layer, 4 denotes a sealing portion, 5 denotes a lead frame, and 6 denotes a cap portion. In the QFP type semiconductor package, input / output signals are handled by the lead frame as described above. Increasing the number of lead frames directly improves the performance of the package and the semiconductor chip. The lead frame is sandwiched between the aluminum nitride substrate and the cap, and sealed with a glass-based sealing material.
However, leadframes are generally Cu-based alloys,
It is formed from various alloy components such as an Fe-based alloy and an Al-based alloy, and has a different coefficient of thermal expansion from aluminum nitride. As a result, unbonded portions such as cracks are likely to occur in the sealed portion due to the thermal stress generated by the thermal expansion difference between the lead frame and the aluminum nitride caused by the heat treatment at the time of sealing and the movement of the semiconductor chip, and the reliability is not sufficient. It was difficult. In the present invention, it has been found that the crack is caused not only by the difference in thermal expansion between the lead frame and aluminum nitride but also by the variation in the thickness of the oxide film on the aluminum nitride substrate. .

That is, if the thickness of the oxide film on the aluminum nitride substrate varies, more specifically, if the difference between the maximum value and the minimum value of the film thickness exceeds 0.2 μm, it becomes unnecessary due to the nitrogen gas ejection as described above. This causes excessive stress concentration, which is unnecessarily affected by the thermal stress based on the difference in thermal expansion between the lead frame and the aluminum nitride substrate, but the difference between the maximum and minimum oxide film thickness is 0.2 μm or less. If it is, unnecessary stress concentration can be prevented, so that the influence of thermal stress based on the difference in thermal expansion can be minimized. Therefore, in the semiconductor package of the present invention, since unnecessary thermal stress is prevented, generation of nitrogen gas from the sealing portion and the surface of the aluminum nitride substrate can be substantially eliminated. Performance can be improved. Similarly, in the present invention, unnecessary stress concentration on the metallized layer when brazing the semiconductor element onto the aluminum nitride substrate is also prevented, so that the present invention is most suitable for a semiconductor package having a metallized layer and a sealing portion. In a semiconductor package having such a metallized layer and a sealing portion, defects such as blistering of the metallized layer and cracking of the sealing portion can be improved.

The package of the present invention which prevents unnecessary stress concentration is a QFP type package, for example, having a unit area length of 40 mm.
This is particularly effective when the number of input / output signals by a lead frame is increased to 120 or more, and further to 200 or more on an aluminum nitride substrate having a size of 40 mm × 40 mm. In other words, the unit area of the aluminum nitride substrate is reduced. 40
It can be said that it is particularly effective for a small package of mm × 40 mm or less.

The cap portion is preferably made of aluminum nitride similarly to the aluminum nitride substrate, but may be made of ceramic such as aluminum oxide or metal such as aluminum or invar alloy. . As for the presence or absence of the oxide film in the cap portion, it is most preferable that the same material as that provided on the aluminum nitride substrate is provided, but the oxide film of the present invention mainly contains aluminum nitride. This is not an essential configuration because it shows a particularly advantageous effect on a substrate or a package.

Next, the manufacturing method will be described. The manufacturing method is not particularly limited as long as an oxide film of the present invention having no variation in film thickness can be obtained. For example, the following method is available. First, an aluminum nitride substrate is prepared by a known method. A film thickness of 3
An oxide film having a thickness of 1 μm or more or a thickness of 1 μm or more than the finally formed oxide film is provided. By subjecting the oxide film to a polishing treatment such as honing, an oxide film having a thickness of 0.3 μm or more and 2 μm or less and a difference between the maximum value and the minimum value of the film thickness of 0.2 μm or less is obtained.

Although there is no particular limitation on the polishing method, for example, honing, lapping, polishing with abrasive paper, etc. can be applied. An aluminum nitride substrate used for a semiconductor package often has a concave-shaped cross section, and when the metallized layer is present even at the corner inside the concave portion, it is difficult to perform polishing by lapping. Therefore, as a polishing method, honing is preferable, and polishing is performed using fine abrasive grains having a grain number of 200 or more, preferably 200 to 700. If the number of abrasive grains is less than 200, the difference between the maximum value and the minimum value of the oxide film is difficult to be 0.2 μm or less because the abrasive grains are too coarse. On the other hand, if it is finer than No. 700, the difference between the maximum value and the minimum value of the oxide film thickness can be made 0.2 μm or less, but the polishing time is longer than necessary, so that the productivity is not necessarily good.

Further, in order to prevent the part showing the maximum value of the oxide film thickness and the part showing the minimum value of the oxide film from being close to a distance of less than 200 μm, after polishing with an abrasive number of 200 to 400,
Two-stage polishing in which polishing is performed with abrasive grains of number 400 to number 700 is effective. According to such two-stage polishing, the polishing can be performed without damaging the oxide film, which is not considered to be too high in hardness. Therefore, the distance between the portions (points) showing the maximum value and the minimum value of the oxide film thickness is 200 μm. As described above, the thickness can be set to 1000 μm or more.

Regarding the place where the polishing process is performed, it is preferable to polish the place where the metallized layer is provided or the place where the metallized layer is sealed by the sealing material, and it is more preferable to polish the entire oxide film applied to the aluminum nitride substrate. It is.

As a method of forming an oxide film, a method of heat-treating an aluminum nitride substrate in an oxygen-containing atmosphere is preferable. A method of applying a compound which becomes an oxide by heat treatment such as a Si compound or a metal alkoxide, a sputtering method,
Although it is possible to form an oxide film by a method of providing an oxide film by the VD method, it is not always possible to say that the productivity is good because the manufacturing process is complicated and the manufacturing cost is high.

The oxygen-containing atmosphere means that the atmosphere or oxygen is 5 to 3 times.
A nitrogen atmosphere containing 0 vol% is suitable. The heat treatment conditions are 1000 ° C or higher, preferably 1100 ° C or higher and 1400 ° C.
1 hour or more, preferably 2 hours or more in the following temperature range 5
Less than an hour. An oxide film is formed even when the heat treatment condition is lower than 1000 ° C., but when the heat treatment condition is lower than 1000 ° C., the oxide film is not easily formed. On the other hand, if the heat treatment temperature exceeds 1400 ° C., an oxide film having a thick oxide film is formed too much, and a polishing time is unnecessarily long, so that the productivity is not necessarily good. Further, when the heat treatment temperature is 1600 ° C. or higher, the movement of the liquid phase component in the aluminum nitride substrate becomes severe, so that the liquid phase component which further causes blistering of the metallized layer and the like is easily transferred to the substrate surface.

Further, since the aluminum nitride substrate of the present invention preferably has a surface roughness Ra of 0.8 μm or less and a Rmax of 6 μm or less before the oxide film is provided, the surface of the aluminum nitride substrate is also polished. Is preferred. Regarding the surface polishing, it is preferable to grind with a fine grindstone having a grindstone number or a grain number of 200 or more, more preferably 400 or more.

As described above, the aluminum nitride substrate of the present invention is obtained by polishing the surface of the substrate as necessary, performing an oxidation treatment, and further polishing the oxide film. Thereafter, a metallized layer is provided at a necessary place such as mounting a semiconductor element. When used as a semiconductor package, for example, in the case of a QFP type semiconductor package, a lead frame and a cap portion are sealed and bonded with a glass sealing material. Regarding the method of forming a metallized layer, the above-described metallized composition is provided at a predetermined location, and then in the air or in an inert atmosphere such as nitrogen (800 ° C. to 950 ° C.) × (5 minutes to 30 minutes). Provided by heat treatment. If the heat treatment temperature is less than 800 ° C, sufficient bonding strength of the metallized layer cannot be maintained, and if the temperature exceeds 950 ° C, heat is rapidly applied to the metallized layer, so that pores are easily formed in the metallized layer. I will. Regarding heat treatment time
If the time is less than 5 minutes, the joint strength of the metallized layer cannot be maintained.
If the heating time exceeds 0 minutes, the heating effect becomes saturated, and the metal particles forming the metallized layer entering the recesses of the oxide film tend to grow abnormally. Therefore, the metallization forming conditions are preferably the above-mentioned temperature and time, more preferably 830 to 900 ° C. × 7 to 20 minutes.

With respect to a sealing method for a semiconductor package, a glass-based sealing material is applied to a predetermined location, and a lead frame and a cap are provided as necessary. Thereafter, heat treatment is performed in the air or in an inert atmosphere such as nitrogen (800 ° C. to 950 ° C.) × (10 minutes to 60 minutes). At this time, if the heat treatment temperature exceeds 950 ° C. or the heat treatment time exceeds 60 minutes, nitrogen gas is easily ejected from the sealing portion, which is not preferable.

[0037]

EXAMPLES (Examples 1 to 5, Comparative Examples 1 to 3) Thermal conductivity 17
0W / m · k aluminum nitride substrate (Ra: 0.8μm or less, Rm
ax: 6 μm or less) in the air at 1260 ° C. for 3 hours to provide an aluminum nitride substrate with a 3 μm-thick aluminum oxide film (40 mm long × 40 mm wide × 0.635 mm thick)
Was prepared. The entire surface of the aluminum nitride substrate with an oxide film is subjected to honing (shot blasting) using a grindstone having the number of abrasive grains of 300 to form an oxide film having the film thickness and the maximum and minimum values of the film thickness shown in Table 1. Processed to. After that, Ag-Pb-based brazing material was immersed in a nitrogen atmosphere at 820 ° C for 16 min.
The presence or absence of blisters when provided with a width of 20 mm and a thickness of 15 μm was confirmed. Table 1 shows the results. In the present example, when measuring the presence or absence of blisters, the presence or absence of a particle having a maximum diameter of 0.2 μm or more and the number of particles having a maximum diameter of less than 0.2 mm were measured. For comparison, Comparative Example 1 in which the oxide film thickness was thinner than that of the present invention, Comparative Example 2 in which the oxide film thickness was thicker, and Comparative Example 3 in which the difference between the maximum value and the minimum value of the oxide film exceeded 0.2 μm. And In addition, each Example and Comparative Example produced 100 pieces each,
The average value is shown.

[0038]

[Table 1]

As can be seen from Table 1, no blisters having a maximum diameter of 0.2 mm or more were generated in the aluminum nitride substrate according to this example. Further, the number of blisters having a maximum diameter of 0.2 mm or less was in the range of 0 to 2, and the blisters confirmed in Example 4 were as small as a maximum diameter of 20 μm or less. On the other hand, about 1 to 3 blisters of 0.2 mm or more were confirmed in the metallized layer of the comparative example 1 provided with the thin oxide film. Similarly, no large blisters having a maximum diameter of 0.2 mm or more were found in Comparative Example 3, but about 4 blisters having a maximum diameter of less than 0.2 mm were found in a 20 mm × 20 mm metallized layer. This is because the maximum value and the minimum value of the oxide film thickness are 0.8 μm, which is out of the range of the present invention, so that metal particles (for example, Ag particles) mainly constituting the metallized layer enter the portion showing the minimum value and are not dissolved. It is considered that the grains grew. On the other hand, in Comparative Example 2 in which the oxide film thickness was as thick as 3.5 μm, blisters having a maximum diameter of 0.2 mm or more (3 to 5 pieces) and blisters having a maximum diameter of less than 0.2 mm were generated. This is because the oxide film is thick and the difference between the maximum value and the minimum value is large, so the oxide film expands due to the heat treatment in the metallization process, and the metal particles constituting the metallized layer enter the recesses and the metal particles do not dissolve and grow alone. It is probable that a large number of blisters were generated due to the large influence of the swelling.

(Examples 5 to 8, Reference Example 1) Thermal conductivity 180 W
/ m · k aluminum nitride substrate (Ra: 0.7 μm or less, Rma
x: 5 μm or less) in a nitrogen atmosphere containing 20 vol% of oxygen.
An aluminum nitride substrate (length 40 mm x 4 mm) provided with a 4 μm-thick aluminum oxide film by heat treatment at 30 ° C x 2 hours
40 mm wide x 0.635 mm thick). By performing a polishing treatment as shown in Table 2 on the aluminum nitride substrate provided with the oxide film, the average oxide film thickness was 0.7 to 2.0 μm,
The difference between the maximum value and the minimum value was unified to 0.2 μm, and the distance between the position indicating the maximum value and the position indicating the minimum value of the oxide film thickness was changed. For such an aluminum nitride substrate,
Ag-Pb brazing metallized layer of 30mm × 30mm × 18μm, maximum diameter 20μm when heat treatment condition is 870 ℃ × 20 minutes
The presence of the following blisters was confirmed. In each of the examples and reference examples, 100 samples were produced, and the average value was shown.

[0041]

[Table 2]

As can be seen from Table 2, the aluminum nitride substrate provided with the metallized layer according to this embodiment has a maximum diameter of 20 μm.
The number of blisters of m or less was in the range of 0 to 2. In particular, 20
In Examples 5 and 7 in which honing was performed with abrasive grains of Nos. 400 to 700 after performing honing with abrasive grains of Nos. 0 to 400, there was no blister having a maximum diameter of 20 μm or less. That is, the blister itself was not formed. In the two-stage processing, the distance between the maximum value and the minimum value of the oxide film is formed at a distance of 1000 μm or more, so that the variation in the thickness of the oxide film, which causes blisters, is reduced. It can be seen that improvement can be made visually. On the other hand, in Reference Example 1, the difference between the maximum value and the minimum value of the oxide film thickness and the oxide film thickness was 0.
Even if the thickness is 2 μm or less, the distance between the location where the maximum value and the minimum value of the oxide film thickness are likely to be less than 200 μm, so that more than two blisters having a maximum diameter of 20 μm or less are generated. I understood. With respect to the aluminum nitride substrates provided with the metallized layers of Examples 5 to 8 and Reference Example 1, no blisters having a maximum diameter of 0.2 μm or more were observed.

(Examples 9 to 13, Comparative Examples 4 and 5) Aluminum nitride substrate having a thermal conductivity of 190 W / m · k or more (Ra: 0.6 μm)
Rmax: 5 μm or less) and Q using the cap portion
In the FP type semiconductor package, the number of inputs and outputs by the lead frame was set to 160, and the copper alloy lead frame, the aluminum nitride substrate, and the cap were sealed with a glass sealing material. In manufacturing the package, the aluminum nitride substrate and the cap were oxidized and polished to obtain the oxide films provided in Table 3, and then heat-treated at 880 ° C. for 30 minutes as a sealing treatment. At that time, the ratio of the unbonded portion of the sealed portion due to generation of nitrogen gas or the like was confirmed.
Table 3 shows the results. In addition, about the ratio of the unjoined part, arbitrary three places of the sealing part on the aluminum nitride substrate side were measured and the average value was shown.

[0044]

[Table 3]

As can be seen from Table 3, each of the semiconductor packages according to the present embodiment had an unbonded portion of 1% or less. On the other hand, in the case of Comparative Example 4, since the oxide film was thin, nitrogen gas was blown out, and the unbonded portion was 3%, which was extremely high. In Comparative Example 5, the ejection of nitrogen gas was not confirmed because the oxide film was thick, but the unbonded portion was increased to 5% because the thermal expansion of the oxide film was severe.

(Examples 14 to 18, Comparative Example 6) Example 5
The aluminum nitride substrate provided with the metallized layer of the sixth embodiment was used for the QFP semiconductor package of the tenth embodiment. At this time, the maximum diameter of the metallized layer when the number of inputs and outputs by the copper alloy lead frame was changed as shown in Table 4
The number of blisters having a size of 20 μm or less and the ratio of unbonded portions in the sealed portions were confirmed. As Comparative Example 6, the same measurement was performed by preparing a QFP type semiconductor package of Example 18 in which an oxide film formed at a portion other than the metallized layer forming portion and the sealing portion was removed by polishing. In each of the examples and comparative examples, 100 samples were produced, and the average value was shown. Table 4 shows the results.

[0047]

[Table 4]

As can be seen from Table 4, the semiconductor package according to this embodiment has a 16
The number of blisters having a maximum diameter of 20 μm or less was found to be in the range of 0 to 1 even when the number was 0 or more. On the other hand, it was found that the ratio of the unbonded portion of the sealed portion did not deteriorate even if the number of lead frames was increased to 240. On the other hand, in the case where the oxide film was not provided on the entire surface of the aluminum nitride substrate as in Comparative Example 6, both the number of blisters and the ratio of unbonded portions were deteriorated. This is thought to be because the thermal expansion of the oxide film or the influence of the nitrogen gas jetting could not be suppressed because the oxide film was not provided on the entire surface, so that the thermal expansion distortion occurred in the aluminum nitride substrate. Can be According to the semiconductor package of the present invention, it is possible to maintain excellent sealing performance even when the number of inputs and outputs by the lead frame is increased to 120 or more.

(Examples 19 to 21, Reference Example 2) Next, using an aluminum nitride substrate having a thermal conductivity of 180 W / m · k, an aluminum nitride substrate whose surface roughness was changed by polishing the surface was manufactured. . After each aluminum nitride substrate was provided with an oxide film having a thickness of 5 μm at 1200 ° C. for 2 hours in the air, and then subjected to a honing process using # 200 abrasive,
Honing was performed using the No. 2 abrasive. The thickness of the oxide film after each honing process and the difference between the maximum value and the minimum value of the oxide film thickness were measured. Table 5 shows the results.

[0050]

[Table 5]

As can be seen from Table 5, in Examples 19 to 21 in which Ra was 0.8 μm or less and Rmax was 5 μm or less, the difference between the maximum value and the minimum value of the oxide film could be made 0.2 μm or less. On the other hand, in Reference Example 2 in which Ra and Rmax were not in the preferable ranges of the present invention, it was found that when the oxide film thickness was within the range of the present invention, it was difficult to make the difference between the maximum value and the minimum value of the oxide film 0.2 μm or less. . From these results, it was found that in the aluminum nitride substrate and the semiconductor package of the present invention, it is preferable that Ra is 0.5 μm or less and Rmax is 5 μm or less.

[0052]

According to the present invention, in an aluminum nitride substrate having an oxide film provided on the entire surface of the aluminum nitride substrate,
The thickness of the oxide film present at the place where the metallized layer is provided is 0.
By providing a uniform oxide film having a thickness of 3 to 4 μm and a difference between the maximum value and the minimum value of the film thickness of 0.2 μm or less, blisters having a maximum diameter of 0.2 μm or more can be eliminated. Further, even minute blisters having a maximum diameter of 20 μm or less in the metallized layer can be controlled to two or less per unit area of 20 mm × 20 mm. Further, by providing a similar oxide film at the sealing portion of the semiconductor package, it is possible to minimize the occurrence of unjoined portions due to the ejection of nitrogen gas and the thermal expansion of the oxide film at the time of sealing. This is particularly effective in a multi-input / output type QFP semiconductor package in which the number of inputs / outputs by a lead frame is 120 or more.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of an aluminum nitride substrate provided with a metallized layer according to the present invention.

FIG. 2 is a sectional view showing an example of a QFP type semiconductor package of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Aluminum nitride substrate 2 ... Oxide film 3 ... Metallization layer 4 ... Sealing part 5 ... Lead frame 6 ... Cap 7 ... Semiconductor element

Claims (9)

[Claims] In an aluminum nitride substrate provided with an oxide film on the entire surface, the thickness of an oxide film existing at a place where a metallized layer is provided is 0.3 μm or more and 2 μm or less, and the difference between the maximum value and the minimum value of the film thickness is 0.2 μm. An aluminum nitride substrate characterized by the following. 2. The aluminum nitride substrate according to claim 1, wherein the oxide film contains aluminum oxide as a main component. 3. An aluminum nitride substrate having a surface roughness Ra of 0.
3. The aluminum nitride substrate according to claim 1, wherein the thickness is 8 μm or less. 4. The surface roughness Rmax of the aluminum nitride substrate is
4. The aluminum nitride substrate according to claim 1, wherein the thickness is 6 μm or less. 5. The aluminum nitride substrate according to claim 1, wherein no blister having a maximum diameter of 0.2 mm or more exists in the metallized layer. 6. A semiconductor package using an aluminum nitride substrate provided with an oxide film on the entire surface, wherein the thickness of the oxide film existing at a location sealed by the metallization layer and the sealing material is not less than 0.3 μm and not more than 2 μm. A semiconductor package using an aluminum nitride substrate having a difference between a maximum value and a minimum value of a thickness of 0.2 μm or less. 7. The semiconductor package according to claim 6, wherein the portion to be sealed is joined to a lead frame by a glass sealing material. 8. The semiconductor package according to claim 7, wherein the semiconductor package is a QFP type. 9. The number of inputs / outputs by a lead frame is 120.
9. The semiconductor package according to claim 8, wherein the number is equal to or more than one.