JPS62222673A - Schottky barrier type semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To remove a crystal defect and contamination on the surface of a semiconductor base body by forming a recessed section along the periphery of an opening section for an insulating film to the main surface of the semiconductor base body. CONSTITUTION:An insulating film 13 is shaped onto the main surface of a semiconductor base body 11, an opening section is formed to the insulating film 13, and a groovy recessed section 12a is shaped to the periphery of the opening section, using a photo-resist film 15 as a mask. A barrier metallic film 16 is formed so as to coat the opening section, and a metallic electrode film 17 is shaped onto the film 16. According to such constitution, a crystal defect and contamination existing near the main surface of the semiconductor base body 11 can be removed.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a Schottky barrier type semiconductor device that utilizes a surface barrier created by contact between a semiconductor and a metal, and a method for manufacturing the same, and particularly relates to a technique for improving device characteristics. It is.

(Prior Art) Conventionally, there has been known a type semiconductor device in which an insulating film having an opening is formed on the main surface of a semiconductor substrate of one conductivity type, and a barrier metal is formed on the insulating film to cover the opening. It is.

FIG. 6 is a sectional view showing the structure of a conventional Schottky barrier diode, which is a type of Schottky barrier semiconductor device. n doped with arsenic, an n-type impurity, at a high concentration
The specific resistance is 0°5~1Ω・cmO on the + type silicon substrate 1.
An n-type epitaxial layer 2 is deposited to a thickness of 5 to 7 μm, and the surface of this epitaxial layer has a thickness of 5000 to 8000 μm.
A thick silicon oxide film 3 is formed by thermal oxidation. This silicon oxide film 3 is selectively removed by photoetching, and an opening with a tapered periphery is formed at the active region. A barrier metal film 4 made of molybdenum or the like is formed on the silicon oxide film 3 to cover this opening, for example, to a thickness of about 2,000 μm, and an aluminum film 5 is further formed to a thickness of about 8 μm on top of this. Furthermore, a wire 6 is bonded onto this aluminum film. Further, a back electrode 7 is formed on the back surface of the n+ type silicon substrate 1.

(Problems to be Solved by the Invention) In the conventional Schottky barrier diode described above, by forming a tapered portion 3a at the periphery of the opening of the insulating film 3, the electric field concentration directly under the insulating film is alleviated. Although the pressure resistance in this direction is increased, it is difficult to make this taper angle sufficiently small, so there is a drawback that the pressure resistance cannot be made sufficiently high. Furthermore, although a thick silicon oxide film 3 is formed on the surface of the n-type epitaxial eyebrow 2 by thermal oxidation, various defects are introduced into the silicon semiconductor substrate 1.2 during this oxidation treatment. Generally, such defects are called oxidation induced defects.
This causes dislocation and scooking hold, which reduces the Schottky barrier formed between the semiconductor substrate and the barrier metal, and increases the interface state, which affects electrical characteristics. has the disadvantage that the reverse voltage becomes low or fluctuates.

As mentioned above, in order to eliminate electric field concentration at the edge of the insulating film opening, a part of the taper is provided at the periphery of the insulating film opening, and the metal field plate and the insulating film are provided on the tapered part. A portion of the taper reduces the electric field concentration at the edge and increases the voltage in the reverse direction. However, after avalanche breakdown, particularly when a large current flows, a so-called positive creep phenomenon occurs in which the reverse voltage gradually decreases, resulting in a decrease in the value of the reverse voltage. As mentioned earlier, this may be due to crystal defects that occur on the surface of the semiconductor substrate when forming an insulating film, stress or deposition damage when forming a barrier metal or electrode metal film, or due to electric field. Although a taper is provided to prevent concentration from occurring at the periphery of the insulating film opening, this is not perfect, and it is conceivable that the way the electric field is applied changes, particularly after avalanche breakdown, causing the reverse voltage to fluctuate.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide a Schottky barrier type semiconductor device having stable characteristics and a method for manufacturing the same.

(Means for Solving the Problems) The present invention provides a semiconductor substrate of one conductivity type, an insulating film formed on the main surface thereof, an opening formed in the insulating film, and a covering for the opening. In the Schottky barrier type semiconductor device comprising a barrier metal film formed on the insulating film, a recess extending to near the periphery of the opening is formed in the main surface of the semiconductor substrate. It is characterized by:

Furthermore, the present invention provides a step of forming an insulating film on the main surface of a semiconductor device of one conductivity type, and selectively exposing the main surface of the semiconductor substrate to this insulating film in manufacturing a Schottky barrier type semiconductor device. forming an opening as shown in FIG. a step of forming a groove-like recess along the periphery of the opening by etching; a step of etching the periphery of the insulating film opening to give it a rounded shape; and after removing the photoresist film. , forming a barrier metal film on the insulating film so as to cover the opening.

(Function) According to the present invention, by forming a concave portion on the main surface of the semiconductor substrate along the periphery of the insulating film opening, crystal defects and contamination formed on this portion of the main surface of the semiconductor substrate can be removed. Accordingly, it is possible to provide a Schottky barrier type semiconductor device having stable characteristics such as high breakdown voltage and low leakage current. In addition, by forming the recess shallowly, electric field concentration at the edge of a part of the insulating film opening taper is alleviated, and the electric field is stabilized even after runche breakdown, making it possible to effectively prevent reverse voltage fluctuations. can.

In the present invention, a groove-like recess is selectively formed on the main surface of the semiconductor film substrate along the periphery of the insulating film opening, but it is also conceivable to form this recess over the entire opening. However, when etching the entire surface of the opening, areas where crystal defects exist are etched quickly, and it is required that the silicon substrate be as defect-free as possible. therefore,
Accordingly, the yield decreases and the cost tends to increase. Furthermore, since the recesses are formed by dry etching in a plasma atmosphere, organic substances such as polymer or carbon may adhere to the surface. In addition, when performing wet etching using hydrofluoric acid or nitric acid, stain films are likely to occur, resulting in lower yields and higher costs.In contrast, in the present invention, the inside of the insulating film opening is Since the surface of a certain semiconductor substrate is not etched and remains as it is, and a groove-like recess is formed along the periphery of the opening, the above-mentioned problem does not occur, and the yield can be improved and costs can be reduced.

(Embodiment) FIGS. 1(a) to 1(d) are cross-sectional views showing the structure of a Schottky barrier diode, which is an embodiment of the Schottky barrier semiconductor device according to the present invention, in successive manufacturing steps.

An n-type silicon epitaxial layer 12 with a resistivity of, for example, 0.7-1.5 Ω-cm and a thickness of about 5-10 μm is formed on an n-type silicon semiconductor substrate 11 doped with n-type impurities at a high concentration. This is grown to form a semiconductor substrate having an n-on n' structure. Next, a silicon oxide film 13 is formed on the n-type epitaxial layer 12 by thermal oxidation, with a thickness of, for example, 5000 to 800.
FIG. 1(a) shows how the film is formed to a thickness of 0.00 mm.

Subsequently, the silicon oxide film 13 is selectively etched using a photoetching technique, and the silicon oxide film 13 is etched.
An opening 14 having a tapered portion 13a is formed to partially expose the main surface of the n-type silicon epitaxial layer 12. This situation is shown in Figure 1 et al.

Subsequently, the n-type silicon epitaxial layer 12 within the opening of the silicon oxide film 13 is removed by photoetching again.
After selectively forming a photoresist film 15, Freon-based dry etching is performed using the silicon oxide film 13 and photoresist film 15 as a mask, and etching is performed to a depth of 100 to 6000 mm along the periphery of the silicon oxide film opening. A groove-shaped recess 12a is formed. This situation is shown in Figure 1 (C).
Shown below. Although this etching can be performed by wet etching using a mixed solution of hydrofluoric acid and nitric acid as an etchant, the above-mentioned dry etching is preferable because it causes less change in the shape of the tapered portion 13a.

Next, as a pretreatment for barrier metal deposition, the surface is treated with acid, and the tip of the tapered portion 13a of the silicon oxide film is etched, for example, by 50 to 100 degrees or more, to give it a rounded shape. After such treatment, a barrier metal film 16 made of, for example, molybdenum is deposited to a thickness of approximately 500 to 5000 μm, and an electrode film 17 of, for example, aluminum is deposited thereon to a thickness of approximately 5 to 10 μm. The situation is shown in Fig. 1(d). A wire is bonded to this aluminum electrode film 17 in the usual manner to complete the device.

FIG. 2 shows another embodiment of the Schottky barrier diode according to the invention. In the embodiment shown in FIG. 1, the edge of the tapered portion 13a of the silicon oxide film 13 protrudes inward from the periphery of the recess 12a and has an overhang shape. In this example, after selectively cutting the surface of the n-type silicon epitaxial layer 12 through an opening formed in the silicon oxide film 13 to form a groove-like recess with a depth of approximately 500 mm, dilute hydrofluoric acid is used. The edge of the tapered portion 13a is rounded by etching, and the edge of the tapered portion 13a is retracted until it coincides with the periphery of the recess.

FIG. 3 shows yet another embodiment of the Schottky barrier diode according to the present invention. In this example, after forming the silicon oxide film 13 thinly to a thickness of about 1000 to 2500 nm, an opening is formed without tapering, and this opening and the photoresist film formed inside the opening are used as a mask to form an n-type silicon oxide film 13. The silicon epitaxial layer 12 is etched to a depth of, for example, about 3,000 mm to form a groove-like recess 12a.
was formed. With such a structure, a Schottky barrier diode with a high reverse voltage of 50 to 80V can be obtained.

In the present invention, a groove-like recess is formed on the main surface of the semiconductor substrate. However, if this recess is formed too deep, the barrier metal film is likely to break (and the metal electrode film will come into direct contact with the semiconductor substrate). become.

Therefore, in the present invention, the depth of this recess is 100 to 60
00 people, particularly preferably around 1000 people.

The present invention is not limited to the embodiments described above, and can be modified and modified in many ways. For example, in the embodiments described above, the insulating film is composed of a single layer of oxide film, but it may also be a composite insulating film made of different insulating materials. Furthermore, although molybdenum was used as the barrier metal in the above embodiments, other high melting point metals such as chromium, nickel, titanium, tungsten, platinum, etc. may also be used.

Furthermore, in the step of FIG. 1C, the photoresist pattern may be divided into a plurality of parts to form a plurality of irregularities on the surface of the n-type semiconductor layer 12. In this way, the adhesion between the barrier metal and the n-type semiconductor layer is improved, and the forward voltage (1) is further stabilized.

Furthermore, in the above-described embodiments, the peripheral edge of the taper was isotropically etched, but it may also be anisotropically etched using, for example, hydrazine or the like.

In this case, the taper tip does not need to be in an overhanging shape, and the insulating film taper tip may be recessed to the same extent or with an error in the anisotropically etched etching edge.

(Effects of the Invention) According to the present invention described above, since groove-shaped recesses are formed on the main surface of the semiconductor substrate before forming the barrier metal film, crystal defects and crystal defects existing near the main surface of the semiconductor substrate are removed. Since contamination is removed, the drop in breakdown voltage and gravity caused by these crystal defects and contamination, which conventionally occur, are reduced, and a reliable semiconductor device with high breakdown voltage can be obtained. Moreover, in the present invention, since it is only necessary to form a shallow recess, the edge effect of the insulating film can be utilized as is, and it is possible to suppress the drop and fluctuation of the reverse voltage and to have a stable reverse voltage. can.

In addition, in the past, the electric field tended to concentrate near the tip of a part of the insulating film taper, but in the present invention, the electric field is diffused by forming a shallow recess, and the electric field is stabilized even after avalanche breakdown, and the reverse voltage This has the effect of almost eliminating fluctuations in . Therefore, it is particularly suitable for high-voltage Schottky barrier diodes, and by changing the characteristics of the silicon substrate, devices with voltages of 100 V, 150 V, and even higher voltages are possible.

FIG. 4 shows the reverse voltage characteristics of the Schottky barrier diode according to the present invention, and FIG. 5 shows the reverse voltage characteristics of the conventional Schottky barrier diode. Comparing these characteristic curves, it can be seen that the present invention has a harder breakdown characteristic. In other words, an ideal metropolitan government has been achieved in which the reverse voltage is the same regardless of the magnitude of the current value and leakage current is small. This is thought to be because etching removes contamination and crystal defects on the surface of the semiconductor substrate.

In addition, since the recesses are formed extremely shallow, there is no risk of deterioration of withstand voltage due to the amount of etching.Furthermore, the leakage current is small, so there is no difference in reverse voltage between 1 mA and 50 mA, for example, making it suitable for n-type etching. The epitaxial layer can be formed thinner with a lower concentration, thereby making it possible to obtain a semiconductor device with a lower forward voltage (1).

Furthermore, since a groove-like recess was formed along the periphery of the opening without forming a recess over the entire inside of the opening on the surface of the semiconductor substrate, unevenness may be formed on the surface of the semiconductor substrate, and foreign matter may adhere to the surface of the semiconductor substrate. Therefore, the contact state between the barrier metal and the semiconductor substrate becomes stable, and the forward direction thickness (3) becomes stable.

[Brief explanation of drawings]

FIGS. 1(a) to (d) are cross-sectional views showing the configuration of an embodiment of a Schottky barrier semiconductor device according to the present invention in sequential manufacturing steps, and FIGS. 2 and 3 are Schottky barrier semiconductor devices according to the present invention. 4 and 5 are glasses showing the reverse voltage characteristics of the Schottky barrier type semiconductor device of the present invention and the conventional Schottky barrier type semiconductor device; FIG. 6 is a diagram of a conventional Schottky barrier type diode. FIG. DESCRIPTION OF SYMBOLS 11... N-type silicon substrate 12... N-type silicon epitaxial layer 12a... Groove-shaped recessed part 13... Silicon oxide film 13a...
Part of taper 14... Opening 15... Photoresist film 16... Barrier metal film 17... Metal electrode film --^
＾O℃

Claims (1)

[Claims] 1. A semiconductor substrate of one conductivity type, an insulating film formed on the main surface thereof, an opening formed in the insulating film, and a semiconductor substrate formed on the insulating film so as to cover the opening. In a Schottky barrier type semiconductor device comprising a barrier metal film formed on
A Schottky barrier type semiconductor device, wherein a groove-shaped recess is formed on the main surface of the semiconductor substrate along a periphery of the opening. 2. Claims characterized in that the opening formed in the insulating film is tapered, and the periphery of the tapered opening is aligned with the periphery of the recess or protrudes in an overhang shape. The Schottky barrier type semiconductor device according to item 1. 3. The Schottky barrier type semiconductor device according to claim 2, wherein the periphery of the opening is rounded. 4. The Schottky barrier type semiconductor device according to claim 1, wherein the depth of the recess is about 100 to 6000 Å. 5. Forming an insulating film on the main surface of a semiconductor substrate of one conductivity type, forming an opening in this insulating film so that the main surface of the semiconductor substrate is selectively exposed, and forming a periphery of the opening. By etching the main surface of the semiconductor substrate using the tapered insulating film opening and the photoresist film formed inside the opening as a mask, etching is performed along the periphery of the opening. a step of etching the periphery of the insulating film opening to give it a rounded shape; and a step of removing a barrier metal on the insulating film so as to cover the opening after removing the photoresist film. 1. A method for manufacturing a Schottky barrier semiconductor device, comprising the step of forming a film.