JPH01223737A - Semiconductor substrate - Google Patents

Abstract

PURPOSE:To improve the adhesive properties of lamination while enhancing wettability with solder or a solder material by successively laminating a first layer composed of a group of titanium, chromium, molybdenum and tungsten, a second layer consisting of nickel or copper and a third layer made of gold onto the surface of a substrate composed of aluminum nitride. CONSTITUTION:A first layer consisting of at least one kind selected from the group of titanium, chromium, molybdenum and tungsten, a second layer made up of nickel or copper and a third layer composed of gold are laminated and formed onto the surface of a substrate consisting of aluminum nitride in succession. It is preferable that the film thickness of the first layer is brought to 100-5000Angstrom in order to increase adhesive strength with an alumina layer while preventing corrosion to aluminum nitride by solder or a solder material. It is desirable that the film thickness of the second layer is brought to 1000-8000Angstrom in order to uniformly laminate the third layer and elevate bond strength with solder or the solder material. It is preferable that the thickness of the third layer is brought to 0.01-2mum in order to ensure bond strength by alloying with solder or the solder material bonded with the surface of the third layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a semiconductor substrate, and particularly to an improvement in a semiconductor substrate having high thermal conductivity.

[Conventional technology]

In recent years, as electronic devices have become smaller and more highly integrated,
An extremely important issue is how to deal with the heat generated from the various semiconductor elements installed in these devices, including SI chips.

Component Design 1 Various proposals have been made in terms of circuit design, materials, etc., but there are not necessarily sufficient means. Among these, semiconductor substrates whose main component is aluminum nitride, which has high thermal conductivity, have been proposed in place of the conventionally used alumina substrates (for example, Japanese Patent Laid-Open No. 177635/1983).
(Refer to Japanese Patent No. 61-119051), it is said to have the advantage of being able to provide semiconductor devices with large capacity and high output due to its high heat dissipation properties, and is attracting attention.

[Problem to be solved by the invention]

However, in terms of thermal conductivity, aluminum nitride has a thermal conductivity of 160 W/mk, compared to 20 W/mk for conventional alumina, so it has great heat dissipation.
There is a problem in that the wettability to metals is extremely low.

Therefore, even if an attempt is made to bond the substrate made of aluminum nitride to the metal forming the conductor layer, there is a problem in that sufficient bonding strength cannot be obtained. On the other hand, attempts have been made to improve wettability by depositing metals such as titanium, copper, etc. on a substrate made of aluminum nitride by vapor deposition. However, the thickness of the layer formed by the above-mentioned vapor deposition method is approximately 9 pcs., which is extremely small.
It is extremely difficult to form it to a thickness on the order of micrometers in order to ensure the bonding strength with the solder or wax that connects the elements. In other words, since internal stress is applied to the laminated layers, they tend to separate from each other, resulting in a problem that the reliability as a semiconductor substrate is significantly lowered.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems existing in the prior art described above, and to provide a highly thermally conductive semiconductor substrate that has high laminated adhesion and improved wettability with solder or brazing material.

[Means to solve the problem]

In order to achieve the above objects, the present invention provides a first layer made of at least one member selected from the group consisting of titanium, chromium, molybdenum and tungsten on the surface of a substrate made of aluminum nitride.

A second layer made of nickel or copper and a third layer made of gold are sequentially laminated. A technical method was adopted.

Note that the first to third layers may be formed after previously forming an alumina layer on the surface of the substrate by heat treatment. In this case, if the thickness of the alumina layer is less than 0.1 μm,
Adhesion with the metal forming the first layer is insufficient and may cause peeling, which is undesirable. On the other hand, if it exceeds 20 μm, it will reduce the thermal conductivity of the substrate and
This is inconvenient because the adhesion with the material deteriorates.

Next, the first layer has a thickness of 100 Å in order to improve adhesion strength with the alumina layer and to prevent corrosion of aluminum nitride by solder or brazing material.
A film thickness greater than or equal to that is required. - If the thickness of the metal film exceeds 5,000, internal stress or strain remains during the formation of the metal film,
This is undesirable because it causes voids or peeling.

The second layer is used to uniformly stack the third layer and to strengthen the bonding strength with the solder or brazing material
Although it requires a film thickness of 100 Å or more.

If the number exceeds 8,000, internal stress or strain remains as in the first layer, which may cause voids or peeling, which is not preferable.

Next, the third layer is coated with a layer of 0.01 to ensure bonding strength by alloying with the solder or brazing material that is bonded to this surface.
A thickness of μm or more is required. Although there is no particular restriction on the upper limit of the thickness, it is economical to limit it to about 2 μm.

〔Example〕

First, an alumina layer with a thickness of 1 μm is formed on the surface of a sintered aluminum nitride plate measuring 1 Omm×1 Omm×2 mm. That is, the aluminum nitride plate was heated at 90°C in the atmosphere or in an atmosphere with an oxygen partial pressure of 0.1 to 0.2 atm.
Heat to 0-1200°C and hold for 10-40 minutes. Note that the thickness of the alumina layer is controlled by heating temperature and/or holding time. Next, the first to third layers are formed on the surface of the alumina layer, each having a thickness of 3000 mm (0.3 μm).
), a nickel layer with a thickness of 7000 mm (0.7 μm), and a gold layer with a thickness of 2500 mm (0.25 μm) are sequentially formed by sputtering.

Molten solder was placed on the semiconductor substrate produced as described above, and wettability with the solder and corrosion state of aluminum nitride were evaluated. The figure is a photograph showing the metal structure of the semiconductor substrate, in which 1 is aluminum nitride, 2 is an alumina layer, 3 is a first layer made of a sputtered titanium film, 4 is a second layer made of a sputtered nickel film, 5 is a third layer made of a sputtered gold film. The third layer 5 forms an alloy layer with tin and lead that constitute the solder, and the layers from the zero-order alumina N2 with sufficient wettability to the third layer 5 are mutually strong. Closely attached.

No peeling phenomenon was observed.

It should be noted that the tin and lead constituting the solder remain in the third layer 5 and do not reach the aluminum nitride 1, so that no corrosion phenomenon due to the solder is observed in the aluminum nitride 1, and it is in a healthy state. It was confirmed.

Next, aluminum pins were fixed to the front and back surfaces of the semiconductor substrate via epoxy resin, and the bonding strength was evaluated. The table shows the results, and the joint strength is 1kg/ram"
It was confirmed that the above conditions were met.

Margin below.

(Note) Film thickness ^1t03: 3μmTi: 10
00 people Ni: 4000 people Au: 2000 people In this example, an example was shown in which the first layer was formed of titanium, but chromium and molybdenum were also used.

They may be made of tungsten, or two
Even if a mixture of two or more species is used, the effect is the same. Also the second
In addition to the sputtering method, physical vapor deposition techniques such as thin deposition method, ion blasting method, and high-speed sputtering method can be used to form the first layer to the third layer. can be used, and the same results as above can be obtained in either case. Note that the first to third layers may be laminated without forming an alumina layer on the surface of the substrate made of aluminum nitride. In this case, the bonding strength will decrease slightly, but the wettability with solder or brazing material will decrease. The effect of improving is exactly the same.

〔Effect of the invention〕

Since the present invention has the structure and operation as described above,
In addition to having good wettability with solder or brazing filler metal,
Sufficient bonding strength with the element to be mounted can be ensured. In addition, there is no corrosion caused by the solder or brazing material, the adhesion between the laminated layers is extremely high, and the reliability of the highly thermally conductive semiconductor substrate can be greatly improved.

[Brief explanation of the drawing]

The figure is a photograph showing the metal structure in an example of the present invention. 3: first layer, 4: second layer, 5: third layer.

Claims (3)

[Claims] (1) Titanium on the surface of a substrate made of aluminum nitride,
It is characterized by being formed by sequentially laminating a first layer made of at least one member selected from the group of chromium, molybdenum and tungsten, a second layer made of nickel or copper, and a third layer made of gold. semiconductor substrate. (2) The semiconductor substrate according to claim 1, wherein an alumina layer is formed on the surface of the substrate by heat treatment. (3) The semiconductor substrate according to claim 1 or 2, wherein each of the first to third layers is formed by physical vapor deposition.