JPS6246561A - Manufacture of schottky barrier type semiconductor device - Google Patents

Abstract

PURPOSE:To remove the peeling phenomenon of a barrier metal by forming a semiconductor film between an silicon oxide film and the barrier metal. CONSTITUTION:A section exposed to the surface is coated with an Al film 8 having high reliability and an n<+> type polycrystalline silicon film 4, the whole silicon chip is coated with a passivation film, and the n<+> type polycrystalline silicon functions as a field plate, thus stabilizing electric characteristics even in a high withstanding-voltage element. Oxide films 3a, 3b are formed thinly, thus reducing the generation of microplasma to an n-type semiconductor layer 2 in the lower section of the oxide films. The generation of trouble, such as thermal strain and the crystal defect of OSF, etc. can be inhibited. Accordingly, the state of the interfaces among the oxide films 3a, 3b and the n-type semiconductor layer 2 can be maintained excellently, thus manufacturing a stable Schottky barrier type diode, reverse voltage (withstanding voltage) thereof is hardly varied.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a Schottky barrier type semiconductor device.

BACKGROUND ART A conventional Schottky barrier diode, which is a type of Schottky barrier semiconductor device, uses arsenic as a highly doped n'' substrate to reduce the forward voltage VF of the diode, as shown in FIG. 3 of the attached drawings. A doped silicon semiconductor substrate is used, and an n-type epitaxial layer 2 is formed on it.
For example, resistivity 0.5~1.0Ω, thickness 5~7
This n-type epitaxial growth layer 2 is grown to a thickness of μm.
A silicon oxide film 3 of about 5,000 to 5000 ml thick is formed on the surface of the silicon oxide film 3, and the silicon oxide film 3 is selectively opened using a photoetching technique so as to form a taper, and a barrier metal, especially molybdenum Membrane 5, for example 2
The wire wire 10 is formed on the barrier metal film 5 to a thickness of about 0,000, and then taken out using an assembly technique on the barrier metal film 5. At this time, the wire wire 10 is made easier to take out using solder 9, which is an alloy of tin and lead. Therefore, a deposited film 8 of another metal such as a Ni-Au film or copper is formed, and a thick wire 10 is taken out on top of the deposited film 8. The method of taking out the wire by welding solder takes into consideration the forward surge characteristics of the diode, but this method takes into consideration the time required for melting and solidifying the solder, variations in the thickness of the solder, and the n-type epitaxial growth that occurs at this time. The effects on device characteristics, such as thermal stress on layers and barrier metal films, cannot be ignored.

Especially from a cost perspective, there is room for consideration in simplifying the method of extracting wires, and recently, IC
There is a tendency to simplify the process by using wire bonding, which is used in power transistors and other devices. There is a conventional Schottky barrier diode that uses this conventional wire bonding method, but since this conventional one does not use solder, the Ni-
It is as if an Affi film is used instead of the Au film 8. Considering the forward surge characteristics of the diode, the thickness of the Al film 8 is made as thick as 7 to 10 μm, and the wire 10 is connected to this Aβ film by ultrasonic bonding without using the solder 9 to connect the electrode. I'm taking it out.

Problems to be Solved by the Invention However, even in such conventional methods, there are various problems as described below.

First, by forming a thick Aj2 film 8 of 7 to 10 μm on the molybdenum film 5, Mo-A
j! It is often seen that peeling phenomenon occurs in the molybdenum film 5 during pattern etching of the film or during heat treatment of the metal electrode film (not shown) formed on the back surface of the n-type semi-molar substrate 1. . In particular, M O on the silicon oxide film 3
-A 12 film plays the role of a field plate for the purpose of stabilizing the potential, making it easier to extend the depletion layer, and making it easier to obtain a withstand voltage, so it is a problem that the phenomenon of peeling occurs in this part. This point will be discussed in more detail below.

Here, the linear expansion coefficient of molybdenum is 5xlo-6/deg
, which is relatively close to 3 x 10-b/deg- for silicon. However, the 6×10
It is one finger smaller than -5/deg. This shows that molybdenum on a silicon oxide film is subject to greater stress and is more likely to peel off due to the difference in expansion coefficient than molybdenum on silicon. Furthermore, the coefficient of linear expansion of Al is 23 x 10-'/deg, which is the largest. Therefore, by heat treatment of the back electrode film, Mo-Al-5in2
The greatest stress occurs during this time. Therefore, Mo A
The edge portion of the film lifts up, the Mo film lifts off the oxidized top, and the Mo film peels off during chip assembly processes such as wire bonding. This peeling of the molybdenum film is proportional to the thickness of the Al film formed on the molybdenum film, and the thicker the Al film is, the better it is in terms of the forward surge characteristics of a Schottky barrier diode, and a minimum of 7 to 10 μm or more is required. Ru. Therefore, here, Mo on the silicon oxide film
- When Al flakes occur, their role as a field plate is weakened, and if the flaking phenomenon progresses further and reaches the active area of silicon, it may be caused by contamination during resin sealing of the device. There are reliability issues, and even damage to the device due to current concentrating in one place.
This is undesirable as it may cause poor wire bonding connections.

From the point of view of device characteristics, the reverse voltage (breakdown voltage) of a Schottky barrier diode is greatly affected by the edge effect of the opening in the insulating film, and as a method to avoid concentration of electric field due to the edge effect, the method described above has been used. A field plate method and a method in which the silicon oxide film opening is tapered have been adopted. Further, the reverse voltage (breakdown voltage) of the Schottky barrier diode after breakdown due to the applied voltage varies and becomes unstable depending on the state of the interface between the oxide film 3 and the n-type semiconductor N2. That is, thermal strain due to the temperature when forming the oxide film 3 or defects such as O, S, and F are introduced onto the n-type semiconductor layer 2 immediately below the oxide film 3.

The thicker the oxide film 3, the more these defects are introduced, and the more likely the breakdown voltage will fluctuate after breakdown. Furthermore, peeling of the M O-Al film is likely to occur.

An object of the present invention is to provide a method for manufacturing a Schottky barrier type semiconductor device that eliminates the problems of the prior art as described above.

Means for Solving the Problems The method of manufacturing a Schottky barrier type semiconductor device according to the present invention includes the steps of forming a relatively thin insulating film on the main surface of a semiconductor layer of one conductivity type, and forming a semiconductor layer on the insulating film. a step of selectively forming a mask material layer on a portion of the semiconductor film other than a portion corresponding to a planned activation region; and a step of forming a mask material layer on the semiconductor film using the mask material layer as an etching mask. forming an opening in the semiconductor film by etching so that its edge has a tapered shape; and forming a tapered portion of the semiconductor film by deforming a portion of the mask material layer that protrudes in an overhang over the opening in the semiconductor film. a step of etching the insulating film opening in the insulating film using the deformed mask material layer as an etching mask so that the edge thereof has a tapered shape; and a step of forming a barrier metal so as to cover the surface of the semiconductor layer exposed at the surface of the insulating film opening and reach onto the semiconductor film.

Embodiments Next, the present invention will be described in more detail with reference to embodiments of the present invention based on FIGS. 1 and 2 of the accompanying drawings.

FIGS. 1A to 1E are cross-sectional structural diagrams for explaining each step of the manufacturing process of a Schottky barrier diode using molybdenum as a barrier metal as an embodiment of the present invention.

In order to manufacture this Schottky barrier diode of the present invention, an n-type semiconductor N2 having a lower concentration than this is formed on an n-type semiconductor substrate i, as schematically shown in FIG. Then, on this, a thin oxide film 3a of about 1000 layers and C
Approximately 300 230M3b formed using the VD method and approximately 8
After forming a polycrystalline silicon film 4 that does not contain about 0,000 impurities, the polycrystalline silicon film 4 is subjected to, for example, a dose of 5 x 10 "cs-" and an acceleration energy of 40K.
N-type impurity ions 4a of about eV are implanted.

Subsequently, as shown in FIG. 1B, a photoresist film 7 as a mask material layer is formed on a portion of the polycrystalline silicon film 4 other than the portion corresponding to the planned activation region using a photoetching technique. After selective patterning is performed, isotropic dry etching is performed using the photoresist film 7 as an etching mask, for example, by gas enchantment of freon and oxygen. The etching speed of the surface layer of the polycrystalline silicon film 4 near the surface into which the n''' type impurity 4a is ion-implanted is several times faster than that of the lower layer which is not implanted with the n' type impurity. The polycrystalline silicon film 4 has a tapered edge at the polycrystalline silicon film opening.

Next, as shown in FIG. 1(B), the photoresist film 7 which is polycrystalline and protrudes in an overhang shape over the opening of the silicon film is subjected to a heat treatment at, for example, about 135 to 180°C, thereby removing the overhang. As shown in FIG. 1C, the photoresist film 7 is softened and reflowed to cover the tapered portion of the polycrystalline silicon film 4 and adhere tightly to the PSG film 3b.

Next, the PSG film 3b and oxide film 3a are etched using an HF-based etchant using the reflowed photoresist film 7 as an etching mask. As is well known, a PSG film has a faster etching speed with an HF-based etchant than an oxide film. Therefore, for example, using approximately 1 to 5% HF-based etchant, the PS'G film 3
By etching the oxide film 113a and the oxide film 3a, a taper of about 5 to 10 degrees is formed at the edge of the oxide film opening of the 1000-meter thick oxide film 3a. This taper improves the spread of the depletion layer at the opening of the oxide film, that is, prevents the breakdown voltage from becoming low due to the edge effect of the Schottky diode, and makes it possible to obtain a high breakdown voltage. After that, the photoresist film 7 is removed, as shown in FIG. 1(D).

Subsequently, as shown in FIG. 1E, a barrier metal, for example, a Mo film 5 is formed so as to cover the surface of the n-type semiconductor layer 2 exposed through the oxide film opening and reach the polycrystalline silicon film 4. is formed to a thickness of about 4000 mm, and an Al film 8 for wire extraction is formed thereon to a thickness of about 7 μm.

Next, FIGS. 2(A) to 2(D) are cross-sectional structural diagrams for explaining each step of the manufacturing process of a Schottky barrier diode using molybdenum as a barrier metal as another embodiment of the present invention. Yes, this example will be explained below.

First, as schematically shown in FIG. 2(A), an n-type semiconductor layer 2 with a lower concentration than this is formed on an n-type semiconductor substrate 1, and a thin oxide film of about 1,300 layers is formed on this. 3, about 80
After forming a polycrystalline silicon film 4 that does not contain impurities and has a thickness of approximately 0.000 mm, n4 type impurity ions 4a are implanted into the polycrystalline silicon film 4 in the same manner as in the previous embodiment.

Next, as shown in FIG. 1(B), an opening is formed in the polycrystalline silicon film 4 and at the same time a tapered portion is formed at the edge of the polycrystalline silicon film 4 in the same manner as in the step of FIG. form. Next, by over-etching, for example, the oxide film 3 is irradiated with Freon radical ions 3c in a plasma atmosphere, and adheres to the surface layer of the oxide film 3. The surface layer of the oxide film 3 to which the freon radical ions 3C are attached is etched at a higher speed with, for example, an HF-based etchant than the lower layer of the oxide film 3 to which the freon radical ions 3C are attached.

Next, as shown in FIG. 2(C), for example, from 135°C to
Reflow the photoresist film 7 by heat treatment at 180°C,
Using this reflowed photoresist film 7 as a mask,
An opening is formed in the oxide film 3 in a self-aligned manner, and a tapered portion is formed at the edge of the opening by utilizing the above-mentioned properties.

Subsequently, the state in which the photoresist film 7 was removed is shown in Figure 2 (
It is shown in D). Hereinafter, the first
M as a barrier metal in the same manner as in the process shown in Figure (E).
An O film and an Al film for wire extraction are formed.

In the above-described embodiments of the present invention, a case was explained in which a Schottky barrier diode was manufactured; however, the present invention is not limited thereto; for example, a Schottky TT
It can be similarly applied to Schottky L, Schottky 1''L, etc. and is effective.Also, in the above embodiment, polycrystalline silicon 4 was used as the semiconductor film, but other materials such as amorphous silicon, Alternatively, metal silicide may be used.Furthermore, the film thickness of the semiconductor film (polycrystalline silicon) was set to 8000, but this value was set to prevent the MO from breaking. The thickness of the semiconductor film is not particularly limited as long as it does not cause any problem even if it is cut at the edge of the semiconductor film.Moreover, MO is used as the barrier metal, but Cr may also be used.

A high melting point metal such as N i ST I SWs P may also be used.

Effects of the Invention As described above, according to the present invention, the peeling phenomenon of the barrier metal, which was the biggest drawback in conventional structures, can be completely eliminated by providing a semiconductor film between the silicon oxide film and the barrier metal. can. Furthermore, in the Schottky barrier type semiconductor device according to the present invention, the surface exposed portion is made of a highly reliable Al film, and outside the Al film is an N-type packed crystalline silicon which also has excellent reliability. Since the entire film-covered silicon chip is covered with a passivation film and the n-type packed crystal silicon field plate moves, even a high breakdown voltage element can have stable electrical characteristics.

Further, according to the present invention, a semiconductor film is provided between the silicon oxide film and the barrier metal, but the silicon oxide film opening for forming the active region can be formed without requiring a special lithography step related to this process. Since the semiconductor film 4 can be formed in a self-aligned manner and accurately by the same photolithography process, it is possible to manufacture a Schottky barrier type semiconductor device with high productivity and excellent characteristics.

Furthermore, according to the manufacturing method of the present invention, the oxide films 3a, 3
By forming the n-type semiconductor layer 2 thinly, the n-type semiconductor layer 2 below
It is possible to reduce the generation of microplasma, and for example, it is possible to suppress the generation of crystal defects such as thermal strain and O3F. Therefore, the interface state between the oxide films 3a, 3 and the n-type semiconductor layer 2 can be maintained in good condition, and the reverse voltage (
A stable Schottky barrier diode with no fluctuation in breakdown voltage can be achieved.

Further, according to the present invention, the oxide films 3a, 3 need only be formed thinly, so that the oxidation time for this can be shortened. Therefore,
There is no rise of n° impurities from the n° type semiconductor substrate Fi1, and an element with high breakdown voltage and excellent forward voltage can be obtained.

[Brief explanation of the drawing]

FIGS. 1(A) to (E) of the accompanying drawings are cross-sectional structural diagrams for explaining each step of the manufacturing process of a Schottky barrier diode as an embodiment of the present invention, and FIG. 2(A)
to (D) are cross-sectional structural diagrams for explaining each step of the manufacturing process of a Schottky barrier diode as another embodiment of the present invention, and FIG. 3 is a cross-sectional view showing an example of a conventional Schottky barrier diode. It is a structural diagram. 1...n゛゛Semiconductor substrate 2...N-type epitaxial semiconductor layer 3.3a.
...Silicon oxide film 3b...PSG film 3C...Freon radical ion 4...
・Polycrystalline silicon film 4a...n゛゛impurity 5...Molybdenum film 7...Photoresist film 8.../L film 10...・Wire line (A) diagram, (C) (D)

Claims (3)

[Claims] (1) A step of forming a relatively thin insulating film on the main surface of a semiconductor layer of one conductivity type, a step of forming a semiconductor film on the insulating film, and a step of forming a relatively thin insulating film on the main surface of a semiconductor layer of one conductivity type, and a step of forming a semiconductor film on the main surface of the semiconductor layer of one conductivity type. a step of selectively forming a mask material layer on a portion of a semiconductor film; and a step of etching a semiconductor film opening in the semiconductor film using the mask material layer as an etching mask so that the edge thereof has a tapered shape. a step of deforming a portion of the mask material layer protruding in an overhang over the semiconductor film opening so as to cover the tapered portion of the semiconductor film; and etching the deformed mask material layer. forming an insulating film opening in the insulating film as a mask by etching so that the edge thereof has a tapered shape; removing the mask material layer; and exposing the semiconductor layer to the surface through the insulating film opening. forming a barrier metal so as to cover the surface of the semiconductor film and reach the semiconductor film. (2) Impurities are ion-implanted into the surface layer of the semiconductor film, and the tapered portion is formed in the semiconductor film using a difference in etching rate between the surface layer and the lower layer of the semiconductor film; The insulating film is composed of an oxide film formed on the main surface of the semiconductor layer and a PSG film formed on the oxide film, and the insulating film is formed by using an etching rate difference between the oxide film and the PSG film. 2. The method of manufacturing a Schottky barrier type semiconductor device according to claim 1, wherein the tapered portion is formed in the insulating film. (3) Impurities are ion-implanted into the surface layer of the semiconductor film, the insulating film is made of an oxide film formed on the main surface of the semiconductor layer, and the etching of the semiconductor film includes Freon. Freon radical ions adhere to the surface layer of the oxide film due to over-etching of the semiconductor film, and the difference in etching rate between the surface layer and the lower layer of the oxide film is used to The method of manufacturing a Schottky barrier type semiconductor device according to claim 1, wherein the tapered portion is formed in the oxide film.