JPS5845833B2 - Shotki barrier semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in Schottky barrier semiconductor devices.

In order to reduce the reverse current and improve the breakdown voltage, conventional Schottky barrier diodes are generally manufactured by etching a portion of the main surface to provide a recess, as shown in FIG. 1, on the main surface of a silicon substrate 1. An insulating surface protection film 2 having an eaves extending over the periphery of the recess is provided, and the barrier metal film 3 is bonded to the silicon substrate 1 through the opening of the surface protection film 2. A Schottky barrier is formed at the interface.

In FIG. 1, reference numeral 4 denotes a contact metal film formed on the barrier metal film 3, and is made of a metal that facilitates electrical connection with the outside.

A feature of this structure is that a space 5 surrounded by the silicon substrate 1, the surface protection film 2, and the barrier metal film 3 is created by deeply etching the silicon substrate 1 to form a recess.

However, in this structure, the silicon substrate 1 of the barrier metal film 3
The electric field concentration at the peripheral edge portion 6 of the joint with the wire cannot be ignored, and the current is concentrated in this portion 6, resulting in a disadvantage that the overcurrent withstand capacity is small.

As a structure to improve this drawback, we have already proposed the structure shown in Figure 2 (Japanese Patent Application No. 130269/1982).
.

In FIG. 2, 2 is an insulating surface protection film, 1 is a silicon substrate, 3 is a barrier metal film made of metal silicide, and 4 is a contact metal film, which is made of Cr, Ni, and Au.
It consists of a layered metal film.

In this structure, the barrier metal film 3 is formed so as to be bonded to the entire surface of the recessed wall surface of the silicon substrate 1, so the curvature of the circumferential portion of the barrier metal film 3 becomes thicker, and the concentration of the electric field is alleviated. The overcurrent withstand capacity is improved by more than 10 times compared to the conventional one.

By the way, when the diode chip shown in FIGS. 1 and 2 is assembled into a package, the back surface of the silicon substrate 1 and the surface of the contact metal film 4 are soldered.

However, in the structures shown in Figures 1 and 2,
The maximum temperature for soldering to the contact metal film 4 is 200°C.
If the temperature rises further, the reverse current of the diode will increase and the breakdown voltage will decrease.

Yet another drawback is that the structure shown in FIGS. 1 and 2 weakens the adhesion between the barrier metal film 3 and the contact metal film 4 due to soldering, resulting in damage due to thermal cycles or intermittent energization. , the barrier metal film 3 and the contact metal film 4 are separated, and the diode becomes electrically open.

As a result of investigating the cause of this, it was found that the solder material was
It has become clear that this is because it diffuses through the barrier metal film 3, reaches the barrier metal film 3, further diffuses through the barrier metal film 3, reaches the interface between the barrier metal film 3 and the silicon substrate 1, and becomes alloyed with silicon. .

The present invention was made in view of the above points, and a film for preventing the diffusion of solder material is provided between the contact metal film and the nickel-palladium alloy silicide barrier metal film, thereby achieving both of the above. The present invention provides a Schottky barrier semiconductor device that can prevent a decrease in adhesive strength between metal films and a decrease in breakdown voltage.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In FIG. 3 showing an embodiment of the present invention, 2 is a surface collapse protective film such as silicon oxide, 1 is a non-N+ type silicon substrate, 3 is a barrier metal film made of nickel-palladium alloy silicide, and 4 is a contact metal. The film 7 is a solder diffusion prevention film that prevents solder material from diffusing.

Experiments were conducted using high melting point metals such as tantalum, tungsten, titanium, and molybdenum as materials for the solder diffusion prevention film 7.

As a result, tantalum gave the best overall results.

When a tantalum film with a film thickness of 2.40 OA was used as the solder diffusion prevention film 7, there was no increase in reverse current and no decrease in breakdown voltage was observed even when soldering was performed at 350°C.

Regarding adhesion, the structure shown in Fig. 2 has an adhesion force of 4 to 7 kg after soldering, but the structure shown in Fig. 3 has a tantalum film formed to a thickness of 3.40 OA. The ones I made were as large as 15 to 20 ky.

Furthermore, in the case of intermittent energization, in the structure shown in Fig. 2, the diode becomes electrically open with i, ooo cycle stability, but in the structure shown in Fig. 3, which uses tantalum, The diode did not become electrically open even after 10,000 cycles.

Among the above-mentioned solder diffusion prevention materials, tungsten is hard and brittle, and when formed into a thin film, cracks easily occur, and it has no effect of preventing solder material diffusion.

Titanium inherently increases the reverse current of the diode, making it unsuitable for this purpose.

Molybdenum is chemically unstable and tends to corrode, especially in the presence of moisture, making it unsuitable for this purpose.

Compared to these, tantalum does not have the above-mentioned drawbacks and has a remarkable effect of preventing solder diffusion.

Further, as a result of experimenting with a tantalum nitride film and a multilayer film of a tantalum film and a tantalum nitride film instead of the tantalum film, it was found that they have a solder diffusion prevention effect equal to or greater than that of the tantalum film.

Therefore, the solder diffusion prevention film 7 may be made of tantalum, tantalum nitride, or a mixture thereof.

An example of a method for manufacturing the device of this invention will be described below.

First, a non-N epitaxial silicon substrate 1 with an orientation of 111 is prepared.

In this case, the resistivity of the N layer is 0.6-0.8.2-m, the thickness is 8-10 μm, and the resistivity of the N-layer is 1-5X10-2
7-am, and the thickness is 250 μm.

Next, a thermal oxide film 2 with a thickness of 1.4 μm is applied to the surface of the epitaxial layer.
An ohmic contact is formed on the back surface of the silicon substrate 1 by a conventional method.

After that, the thermal oxide film 2 is coated with a 2.9 mm x
Create a pore of 2.9 mvt.

Then, nitric acid: acetic acid: hydrofluoric acid = 7:2:1 (vol, ratio 2
The silicon substrate 1 is etched to a depth of 4μ by etching at a temperature of 5°G.

After that, 1.0OOOO of nickel-palladium (50:50 at%) alloy was applied to one surface of the etched silicon substrate.
Plate to thickness A.

After that, sintering at 500°C for 15 minutes in a nitrogen atmosphere,
Produces silicide of nickel and palladium.

Then, as the solder diffusion prevention film 7, a Kuntal film is formed by a four-pole sputtering method.

After evacuating the vacuum chamber to 5X10-8 Torr, 2.6X10
It is obtained by sputtering at a target voltage of 500 mA and a target current of 100 mA.

The film formation rate was 110A/ff1M, and the film was formed to a thickness of 2.4ooA.

The tantalum formed was beta tantalum.

Thereafter, a three-layer film of chromium, nickel, and gold is formed on the lithium/tal film by electron beam evaporation.

In this process, the vacuum chamber is evacuated to 1O-8 Torr using a sorption pump and an ion pump, and the chromium film is deposited on the silicon substrate 1 at room temperature. After forming the silicon substrate 1 to a thickness of oooA, the silicon substrate 1 is heated in a vacuum at 350°C.
After heat treatment for 0 minutes and cooling the silicon substrate 1 to room temperature, a nickel film is formed to a thickness of 7.0 OOA and a gold film is formed to a thickness of 12.0 OOA.

Vapor deposition and heat treatment were performed at 5×10 −7 Torr or less.

Thereafter, unnecessary portions of the gold, nickel, chromium, and tantalum films are etched away by ordinary photolithography.

Through the above steps, a desired Schottky barrier diode as shown in FIG. 3 was obtained.

As described above, according to the present invention, since the solder diffusion prevention film is provided between the barrier metal film of nickel-palladium alloy silicide and the contact metal film, the solder is not soldered to the contact metal film at high temperature during assembly. Also, it is possible to obtain a Schottky barrier semiconductor device in which the breakdown voltage does not decrease due to reverse current amplification, and the contact metal film and barrier metal film do not separate.

[Brief explanation of the drawing]

FIGS. 1 and 2 are sectional views of essential parts of a conventional Schottky barrier diode, respectively, and FIG. 3 is a sectional view of essential parts of an embodiment of the present invention. In the figure, 1 is a silicon substrate, 3 is a nickel-palladium alloy silicide barrier metal film, 4 is a contact metal film, and 7 is a solder diffusion prevention film. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] t No in which a recessed portion of a predetermined depth is formed in a part of the main surface.
n N+ type silicon substrate, a nickel-palladium silicide barrier film formed to be bonded to at least a portion of the wall surface of the recess of the silicon substrate, a solder diffusion prevention film formed on the barrier film, and the solder. A Schottky barrier semiconductor device including a contact metal film formed on a diffusion prevention film. 2 The solder diffusion prevention film is made of tantalum, tantalum nitride,
2. The Schottky barrier semiconductor device according to claim 1, wherein the Schottky barrier semiconductor device is made of a mixture thereof. 3. The Schottky barrier semiconductor device according to claim 1 or 2, wherein the contact metal film has a three-layer structure of chromium, nickel, and gold.