JPS63138770A - Manufacture of schottky barrier type semiconductor device - Google Patents

Abstract

PURPOSE:To form a guard ring easily without using a photoetching technique by a method wherein a material layer containing reverse conductive type impurities is formed on the insulating film formed on a substrate, and the insulating film is underetched. CONSTITUTION:When an oxide film 23 exposed in an aperture part 24a is etched using a p<+> type polycrystalline film 24 as a mask, the oxide film 23 is underetched, an aperture part, which is retreated from the aperture part 24a of the p<+> type polycrystalline silicon film 24, is formed on the oxide film 23. Then, a CVD-SiO2 film 25 is deposited. In this case, as the oxide film 23 is underetched, the CVD-SiO2 film is not formed on the above-mentioned part. Then, a guard ring 26 consisting of a p<+> type semiconductor layer is formed in a self-matching manner at a part located in the vicinity of the aperture on the p<+> type polycrystalline silicon film 25 by performing a heat treatment, As a result, the guard ring can be formed accurately in a self-matching manner without increasing the number of photetching processes.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing a Schottky barrier type semiconductor device that utilizes a surface barrier created by contact between a semiconductor and a metal, and in particular relates to a technique for reducing the number of photoetching processes. It is related to.

(Prior Art) A Schottky barrier type semiconductor device is conventionally known 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. be.

FIG. 4 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 on the pear-shaped silicon substrate is 0.5 to 1Ω.
A type epitaxial layer 2 is deposited to a thickness of 5-7 μm;
A thick silicon oxide film 3 of 5,000 to 8,000 layers is formed on the surface of this epitaxial layer by thermal oxidation. This silicon oxide film 3 is selectively removed by photoetching, and an opening 3a having 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 approximately 2,000 mm, and an aluminum film 5 is further formed on the silicon oxide film 3 to a thickness of approximately 8 μm.
Further, 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 part of the taper at the periphery of the opening 3a 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. Further, a thick silicon oxide film 3 is formed on the surface of the n-type epitaxial layer 2 by thermal oxidation, and during this oxidation process, the silicon semiconductor substrate 1. 2, various defects are introduced. Generally, such defects are called oxidation induced defects.
This causes disrogation 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. The disadvantage of the receiver is that the reverse voltage may be low or fluctuate.

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 the 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 reverse voltage may fluctuate due to changes in the way the electric field is applied, especially after avalanche breakdown.

Furthermore, as another conventional example for solving the above-mentioned effects of crystal defects and damage caused by vapor deposition, there is also known a method in which a guard ring is formed along the edge of the oxide film opening to improve the breakdown voltage.

FIG. 5 is a cross-sectional view showing the structure of a conventional Schottky barrier diode having a guard ring during the manufacturing process.

For example, a specific resistance of 0.5 to 2.0 Ω−1 is formed on an nI type silicon substrate 11 doped with n type impurities such as arsenic at a high concentration.
The n-type semiconductor layer 12 is epitaxially grown to a thickness of, for example, 6 to 12 μm, and a thin oxide film 13 of about 1000 layers is uniformly formed on the surface of the n-type semiconductor layer 12, as shown in FIG. 5(8).

Next, a p0 type half layer 14 was formed by ion implantation using photoetching technology so as to surround the part that would later become the active region, and then a 5,000 thick oxide film 15 was uniformly formed again. Figure 5 (shown in bl.

Next, the oxide film 15 above the active region is selectively etched using a photoetching technique to form an opening 15a, as shown in FIG. 5 (C1).

Next, a barrier metal film 16 made of a high melting point metal such as molybdenum is formed on this to a thickness of about 2000 to 3000 μm, and a metal electrode film 17 made of aluminum or the like is further formed on it to a thickness of about 5 to 10 μm. FIG. 5(d) shows how a Schottky barrier diode is completed by forming the back electrode film 18 on the back surface of the n-type substrate 11.

In such a conventional device, a photo-etching process is required for each cap to form a guard ring made of the p-type thick conductor layer 14, which complicates the manufacturing process, lowers the yield, and increases costs. There is a drawback. Also,
Since the difference between the openings 15a of the oxide film 15 is large, strong stress is generated in the barrier metal film 16 made of a high melting point metal such as molybdenum in this part, resulting in deterioration of characteristics and disconnection of cranks, etc. , the upper metal electrode film 17 and the semiconductor substrate came into contact through this crank, and reliability often deteriorated. Furthermore, in the case of an IC, it is necessary to provide a margin for alignment, which has the drawback of limiting miniaturization.

Therefore, an object of the present invention is to be able to easily form the above-mentioned guard ring without using photo-etching technology, to form the guard ring accurately in a self-aligned manner, and to form an opening in the oxide film. The purpose of the present invention is to provide a method for manufacturing a Schottky barrier type semiconductor device, which can alleviate strong stress on the barrier metal by making it smooth, improve device characteristics, and improve reliability. .

(Means and effects for solving the problems) The present invention has the following features:
In manufacturing a Schottky barrier type semiconductor device having a guard ring to improve device characteristics, there is a step of forming an insulating film on the surface of a semiconductor substrate of one conductivity type, and an impurity of the opposite conductivity type is formed on this insulating film. a step of forming an aperture by patterning this material layer; and a step of under-etching the insulating film using the aperture made in the material layer as a mask to form an aperture set back from the aperture. forming a guard ring made of a semiconductor layer of an opposite conductivity type along the opening by diffusing an impurity of an opposite conductivity type from the material layer into the semiconductor substrate; The method is characterized by comprising a step of forming a barrier metal film on the surface of the semiconductor substrate surrounded by the material layer and the opening.

According to the method of the present invention described above, a material layer containing impurities of the opposite conductivity type, such as a polycrystalline silicon layer, is formed on an insulating film formed on a semiconductor substrate of one conductivity type, and the insulating film is under-etched. By doing so, the semiconductor substrate and the polycrystalline silicon layer are made to face each other along the opening, and heat treatment is performed to diffuse impurities of opposite conductivity type from the polycrystalline silicon into the semiconductor substrate to form a guard ring in a self-aligned manner. Therefore, the opening of the insulating film and the guard ring can be formed in one photoetching process, which simplifies the manufacturing process.

Further, in a preferred embodiment of the present invention, after under-etching the insulating film, an oxide film such as Cv low SiO□ is formed on the surface, and then heat treatment is performed to form a guard ring.
Thereafter, the oxide film is anisotropically etched to form a clean sidewall on the wall of the opening in the insulating film, and then a barrier metal film is formed. In such a case, since a sidewall made of a smooth oxide film is formed at the opening in the insulating film, strong stress will not be generated on the barrier metal film formed on it, improving device characteristics and reliability. This will improve your sexuality.

(Example) FIGS. 1(a) to 1(f) are cross-sectional views showing the structure in successive steps in manufacturing a Schottky barrier diode by the manufacturing method of the present invention.

First, an n゛゛silicon substrate 2 containing a high concentration of n-type impurities is prepared.
1, with a specific resistance of 1 to 2 Ω-1 and a thickness of 6 to 10 μm
FIG.
Shown in l.

Next, about 1,000 to 20
FIG. 1B shows a silicon oxide film 23 having a thickness of about 7,000 wafers and a polycrystalline silicon film 24 having a thickness of about 7,000 wafers formed thereon. This polycrystalline silicon film 24 is doped with a p-type impurity, such as boron, at a high concentration.

Next, photoetching technology is used to remove the p-p layer above the active region.
FIG. 1(b) shows how the ``type polycrystalline silicon film 24 is selectively under-under to form an opening.

The opening that defines this opening is indicated by the reference numeral 24a.

Next, the oxide film 23 exposed in the opening is etched using the p+ type polycrystalline silicon film 24 as a mask.

At this time, the oxide film 23 is underetched as shown in FIG. 1(C), and has an opening recessed from the opening 24a of the p9 type polycrystalline silicon film 24.

Next, the CVD-5iO2 film 25 is
Figure 1(d) shows how the particles are deposited to the thickness of a person. In this case, since the oxide film 23 is under-etched,
The p'-type polycrystalline silicon film 24 near the opening and the surface of the n-type epitaxial layer 22 directly oppose each other, and no CVD-5in film is formed in this portion.

Next, heat treatment is performed to diffuse boron, which is a p-type impurity, to the surface of the n-type epitaxial layer 22 near the opening of the p-type polycrystalline silicon film 25, thereby forming a guard ring 26 made of a p-type semiconductor layer. formed in a self-consistent manner, and further C
FIG. 1(e) shows how the CVD-5in film 25 is anisotropically etched. In this example, further CVD-5iO□
Before etching the film, heat treatment is performed to form silicon oxide in the space between the n-type epitaxial layer 22 and the p-type polycrystalline silicon film 24. A wall 25a is formed on the wall of the opening 24a of the p'-type polycrystalline silicon film 24. However, such oxidation treatment may be omitted and a gap may be left between the epitaxial layer 22 and the polycrystalline silicon film 24 along the opening.

Next, a barrier metal film 26 made of a high melting point metal such as MOl Nl + Cr + P t + Tt is deposited at a thickness of about 2,000 to
A metal electrode film 27 made of AI or the like is formed thereon to a thickness of about 5 to 10 μm, and a back electrode film 28 made of AI or the like is formed on the back surface of the n0 type silicon substrate 21. The completed Schottky barrier diode is shown in Fig. 1(r).

As described above, in this embodiment, the p-type impurity doped into the polycrystalline silicon film 24 is passed through the space formed by under-etching the oxide film 23 to form the n-conductivity type semiconductor substrate 21.
．． Since the guard ring 26 made of the p-type semiconductor layer is formed by diffusing it onto the surface of the p-type semiconductor layer 22, the guard ring can be accurately formed in a self-aligned manner without increasing the number of photo-etching processes. Furthermore, since there is no need to provide an allowance for positioning in the IC, miniaturization can be achieved. Furthermore, since a smooth sidewall 25a made of a CCVD-5in film is formed on the wall of the opening 24a of the polycrystalline silicon film 24, the barrier metal film 27 formed thereon may peel off or break. It is possible to improve device characteristics and reliability without causing any damage.

(Effects of the Invention) According to the present invention described above, since the guard ring 26 made of the p-type semiconductor layer is formed along the periphery of the oxide film opening, the surface of the semiconductor substrate 21, 22 is exposed during the oxidation process. Even in the presence of O5F induced by . Moreover, the guard ring made of this p-type semiconductor layer can be formed precisely along the opening of the oxide film in a self-aligned manner without increasing the photo-etching process, resulting in a significant improvement in productivity. be able to. In addition, since a smooth sidewall 25a is formed at the opening of the oxide film, strong stress is not applied to the barrier metal film 27 formed thereon, and cracks and disconnections do not occur, improving reliability. It will improve.

Furthermore, by changing the impurity concentration of the semiconductor substrate, 1
It is also possible to manufacture elements having a breakdown voltage of 00 V, 150 V, or even higher.

FIG. 2 shows the reverse voltage characteristics of the Schottky barrier diode manufactured by the method of the present invention, and FIG.
This figure shows the reverse voltage characteristics of the Schottky barrier diode manufactured by the conventional method shown in the figure. As is clear from comparing these characteristic curves, the present invention has a harder avalanche breakdown. In other words, ideal characteristics such as equal reverse voltage and low leakage current are obtained regardless of the magnitude of the current value.

Furthermore, in the present invention, the width of the guard ring 26 can be adjusted by controlling the amount of underetching of the oxide film 23 formed on the surface of the semiconductor substrate 21, 22, and this width can be narrowed accurately. This makes it possible to miniaturize integrated circuits. Further, since there is no need to provide a margin for alignment, further miniaturization can be achieved.

[Brief explanation of the drawing]

FIGS. 1(a) to (f) are cross-sectional views showing the structure of a Schottky barrier diode manufactured by the method of the present invention in sequential steps. FIGS. 2 and 3 are sectional views of a Schottky barrier diode manufactured by the method of the present invention. A graph showing the reverse voltage characteristics of a conventional Schottky barrier diode and a conventional Schottky barrier diode. Figure 4 is a cross-sectional view showing the structure of a typical conventional Schottky barrier diode. 21 is a cross-sectional view for explaining a conventional method for manufacturing a Schottky barrier diode. 21... n'-type semiconductor substrate 22... n-type epitaxial layer 23... oxide film (insulating film) 24. ...p0 type polycrystalline silicon film (material layer) 25-C
VD-5iOg1!26... Guard ring 27...
Barrier metal film 28... Metal electrode film 29... Back electrode film Patent applicant TDC Co., Ltd. Figure 1 Figure 1 Figure 2 Figure 3 Figure 4 Figure 7Z Figure 5

Claims (1)

[Claims] 1. A step of forming an insulating film on the surface of a semiconductor substrate of one conductivity type; A step of forming a material layer containing impurities of an opposite conductivity type on this insulating film; and this material layer. forming an opening by patterning the material layer; under-etching the insulating film using the opening made in the material layer as a mask to form an opening in the insulating film that is set back from the opening; , diffusing impurities of opposite conductivity type into the semiconductor substrate to form a guard ring made of a semiconductor layer of opposite conductivity type along the opening; 1. A method for manufacturing a Schottky barrier type semiconductor device, comprising the step of forming a barrier metal film. 2. After under-etching the insulating film, an oxide layer is formed, and then impurities of opposite conductivity type are diffused from the material layer, and the oxide film is anisotropically etched to form the walls of the opening in the insulating film. 2. The method of manufacturing a Schottky barrier type semiconductor device according to claim 1, wherein smooth sidewalls are formed on the semiconductor device.