JPS5845814B2 - Semiconductor device with laminated metal electrodes - Google Patents

Abstract

PURPOSE:To increase bonding strength and obtain satisfactory ohmic connections by composing the collector electrode for mounting a transistor to the conductive layer of a header through a solder foil with the laminated matals composed of Au, T, Ni which are subsequently deposited from the rear of a substrate.

Description

[Detailed description of the invention] The present invention relates to a semiconductor device, particularly its electrode structure.

In a semiconductor device, for example, a single transistor, normally, as shown in FIG. 1, a base region 2 and an emitter region 3 are formed on one surface of a silicon semiconductor substrate 1 serving as a collector, and a base electrode B and an emitter electrode E are formed. A collector electrode C is formed on the top surface and the back surface, and this collector electrode C is directly soldered 6 to the conductive layer 5 of a predetermined header 4.
It is designed to be installed through.

Conventionally, the electrode structure of the electrode directly soldered to the header, that is, the collector electrode C in this case, is a silicon substrate 1.
Either a nickel-Ni layer is deposited directly on the back surface of the nickel layer by electroless plating, a gold-Au layer is directly deposited on the back surface of the nickel layer, or a gold-Au layer is directly deposited on the back surface of the
It was composed of a laminated metal of nickel and Ni, or a laminated metal of gold Au, nickel Ni, and silver Ag.

However, each of these conventional electrode structures has the following drawbacks.

For example, if the collector electrode C is formed by electroless plating a nickel Ni layer directly on the silicon substrate 1, it will be difficult to establish an ohmic connection unless the impurity concentration of the substrate is 1018 atoms/- or higher, especially if the substrate 1 is P-type. In this case, Ni3P precipitates and ohmic connection cannot be established.

In addition, when gold-Au is vapor-deposited, the hardness of the gold-silicon eutectic is relatively high, so if the pellet is large, it will easily break.
It was inappropriate for OS-IC and the like.

In addition, when a laminated metal of gold-Au and nickel-Ni is used, when the nickel-Ni layer is cooled after alloying, the nickel-Ni layer cracks and the solder seeps into the cracks, causing electrode peeling. Cracks in the nickel surface or a silicon-gold-nickel alloy are formed due to interdiffusion with the nickel metal, which impairs soldering workability.

Furthermore, electrodes made of gold-nickel-silver laminated metals are used in semiconductor integrated circuit ICs, etc., but when applied to single-piece power transistors, for example, the amount of solder is large, and when heat is generated, the silver is removed by the solder. Furthermore, due to mutual diffusion of gold and nickel, the gold is also corroded by the solder, resulting in a disadvantage in that the adhesive strength of the electrode to the header deteriorates.

In view of these points, the present invention provides a semiconductor device having electrodes with good adhesion strength and ohmic connection to a header.

An example of a semiconductor device according to the present invention applied to a silicon transistor will be described below with reference to FIG.

In FIG. 2, reference numeral 1 denotes a silicon single crystal substrate serving as a collector, and a base region 2 and an emitter region 3 are sequentially formed on the negative surface thereof by diffusion, and a base electrode B and a While the emic electrode E is formed (the collector electrode C is formed on the back surface of the base 1),
is formed, and this collector electrode C is attached directly onto the conductive layer 5 of a predetermined header 4 via a solder foil 6.

The conductive layer 5 of the header 4 is formed by nickel plating, silver plating, or the like.

Further, as the solder foil 6, lead Pb: 90% by weight, tin Sn:
An alloy foil consisting of 9% by weight and 1% by weight of silver and Ag is used.

Note that 7 is an insulating protective film made of SiO2 or the like.

In the present invention, in such a transistor, an electrode that is directly attached to the conductive layer 5 of the header 4 via a solder foil 6, that is, a collector electrode C, is made of a gold Au layer sequentially deposited on the back surface of the substrate 1.
It is composed of a laminated metal 11 consisting of a first layer 8 mainly made of titanium T1, a second layer 9 made of titanium T1, and a third layer 10 made of nickel Ni.

The first layer 8 mainly made of gold is formed of a gold-Au layer containing approximately 0.3% arsenic As when the base 1 is N-type, and is formed of a gold-Au layer containing about 0.3% of arsenic As when the base 1 is P-type. Trowel form.

The thickness of each metal layer 8, 9, and 10 is as follows:
Range of 00 to 1500 people, layer 9 is 500A to 2000
In the human range, the layer 10 preferably ranges from 0.3μ to 1.5μ.

The reason for this is that, for example, the thickness of the layer 8 mainly made of gold is 500 mm.
If the number is less than the number of people, the ohmic connection to the base 1 will be hindered, and if it exceeds 1500A and the number of people is about 2000 to 3000, cracks will occur on the nickel surface.

Further, the titanium layer 9 includes a layer 8 mainly composed of gold and a nickel layer 10.
If the thickness of the layer is less than 500 people, the effect of preventing mutual diffusion will be significantly reduced;
If it exceeds the number of people, cracks will occur in the titanium layer 9 itself, which is not preferable.

Furthermore, regarding the nickel layer 10, its thickness is 0.3
If it is more than 1.5μ, it is sufficient to remain in the necessary amount even if it reacts with the tin Sn in the solder foil 6 during soldering.On the other hand, if it exceeds 1.5μ, the nickel layer tends to peel off from the titanium layer 9 due to the stress of itself. Also, the resistance of the nickel layer 10 cannot be ignored, which tends to be disadvantageous in terms of characteristics.

Formation of the laminated metal 11 is performed as follows.

First, protect the other surfaces of the substrate 1 except for the back surface on which the collector electrode is to be formed with wax or resist, and soak the back surface of the substrate in a concentrated ammonium fluoride (NH4F) solution for 5 minutes and then apply a hydrofluoric acid solution (H2O:HF= 5:1) for 25 minutes to remove the surface oxide film and perform pretreatment for vapor deposition.

Next, the substrate 1 is placed in a vapor deposition apparatus, and A containing As is first
(in the case of an N-type substrate) is evaporated from a resistive evaporation source, and a layer 8 mainly composed of Au is deposited on the back surface of the substrate.

Next, Ti and Ni are sequentially evaporated using an electron beam evaporation source, and a titanium layer 9 and a nickel layer 10 are sequentially deposited on the layer 8.

In the case of a P type substrate, Au, Ti and Ni can be deposited by a series of electron beam evaporations.

The substrate 1 with successively deposited layers 8, 9 and 10 is then flash alloyed to form the electrode C at a peak temperature of 380 DEG C. to 400 DEG C.

According to the electrode structure described above, since the layer 8 mainly composed of gold is in direct contact with the silicon substrate 1, ohmic properties are improved.

Moreover, since the titanium layer 9 is interposed between the layer 8 mainly composed of gold and the nickel layer 10, mutual diffusion between gold and nickel is prevented, and the adhesion strength deteriorates due to alloying of silicon-gold-nickel. Alternatively, corrosion and peeling due to solder can be avoided and reliable soldering can be achieved.

Also, because of its good ohmic properties, the collector-emitter voltage at saturation in transistors is ■.

B(set) is improved, and since the underlying metal is the nickel layer 10 during soldering, corrosion of the solder is eliminated and there is no deterioration phenomenon, and the heat conduction property, that is, the thermal resistance θT can be improved.

Although the upper electrode is applied to the collector electrode of a transistor, it can also be used for surface electrodes (base and emitter electrodes) of power transistors, etc., or electrodes of other general semiconductor devices.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a conventional semiconductor device, and FIG. 2 is a sectional view showing an example of a semiconductor device according to the present invention. 1 is a semiconductor substrate serving as a collector, 2 is a base region, 3 is an emitter region, 4 is a header, 5 is a conductive layer, 6 is a solder foil, 8 is a layer mainly made of gold, 9 is a titanium layer, and 10 is a nickel layer. , C is a collector electrode, B is a base electrode, and E is an emitter electrode.

Claims (1)

[Claims] 1 A laminated metal electrode is formed by sequentially depositing a gold-based layer, a titanium layer, and a nickel layer on the semiconductor region where the electrode is to be formed, and the thickness of the gold-based layer is 500 mm.
The thickness of the titanium layer is 500 to 1,500 people.
In the range of λ to 2000A, the thickness of the nickel layer is 0.
A semiconductor device having laminated metal electrodes each having a thickness in the range of 3μ to 1.5μ.