JPS63138771A - Schottky barrier type semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To assure stable voltage in direction and withstand voltage by a method wherein a smooth sidewall is formed on the wall of an opening in material layer to form a barrier metal film on the surface of a semiconductor substrate encircled by the sidewall as well as the surface of material layer. CONSTITUTION:An oxide film exposed to an opening is underetched using a p<+>type polycrystalline silicon film 24 as a mask. First, another polycrystalline silicon film 25 deposited on overall surface is anisotropically etched to form a sidewall 25a drawing the smooth contours on the wall of opening 24a of p<+>type polycrystalline silicon film 24. Second, p type impurity is diffused from the part of p<+>type polycrystalline silicon film 24 extending more inwardly than the oxide film 23 to the surface of an n type epitaxial layer 22 to form a guard ring 26. Finally, a barrier metal film 27 is deposited on overall surface. Through these procedures, the barrier metal film 27 can avoid a step disconnection or an exfoliation to assure stable voltage Vf in a forward direction and the withstand voltage.

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 technology for improving device characteristics and a method for manufacturing the same. This invention relates to a technique for simplifying the method.

(Prior art) Schottky barrier type semiconductor devices are 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. It is.

FIG. 5 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
n with a specific resistance of 0.5 to 1 Ω on the ゛-type silicon substrate 1.
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, and an aluminum film 5 is further formed on the silicon oxide film 3 at a thickness of about 8μI.
Further, a wire 6 is bonded onto this aluminum film. Further, a back electrode 7 is formed on the back surface of the n1 type silicon substrate 1.

(Problems to be Solved by the Invention) In the conventional Shosokitovari 7 type diode described above, by forming a tapered portion at the periphery of the opening 3a of the insulating film 3, the electric field concentration directly under the insulating film is alleviated, and the reverse is achieved. 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 layer 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. 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 tapered part is provided at the periphery of the insulating film opening, and a metal film field plate is provided on the tapered part. The tapered part of the insulating film reduces electric field concentration at the edge and increases the reverse voltage.However, after avalanche breakdown, especially when a large current flows, the reverse voltage gradually decreases. , a so-called positive creep phenomenon occurs and the value of the reverse voltage becomes small.As mentioned earlier, this is due to crystal defects that occur on the surface of the semiconductor substrate when forming the insulating film. The taper is used to prevent stress and evaporation damage during the formation of the barrier metal and electrode metal films, or to prevent electric field concentration from occurring at the periphery of the insulating film opening, but this is not perfect and is particularly susceptible to avalanche damage. It is conceivable that after breakdown, the way the electric field is applied changes and the reverse voltage fluctuates.

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. 6 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 n-type silicon substrate 11 doped with n-type impurities such as arsenic at a high concentration.
FIG. 6(a) shows a state in which 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 approximately 1,000 layers is uniformly formed on the surface thereof.

Next, a p-type thick conductor layer 14 was formed by ion implantation using photoetching technology to surround the part that would later become the active region, and then a 5,000-layer thick oxide film 15 was uniformly formed again. Figure 6 (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. 6 (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. 6(d) shows how a Schottky barrier diode is completed by forming a back electrode film 18 on the back surface of the n-thick substrate 11.

In such a conventional device, a photo-etching process is required for each thread 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 these cracks, which often resulted in a decrease in reliability. Furthermore, since it is necessary to provide an alignment margin for ICs, there is a drawback that miniaturization is restricted.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks and provide a Schottky barrier type semiconductor device that can stably obtain a high withstand voltage and a small forward voltage V by providing a guard ring. That is.

Another 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 problem) The Schottky barrier type semiconductor device of the present invention comprises a semiconductor substrate of one conductivity type, an insulating film formed on the surface thereof and having an opening, and a top surface of the insulating film formed on the insulating film. , a material layer having an opening located inward from the opening of the insulating film and containing an impurity of an opposite conductivity type, and the impurity contained in this material layer being diffused to the surface of the semiconductor substrate. a guard ring constituted by a semiconductor layer of opposite conductivity type formed along the opening; a conductive sidewall formed on the wall of the opening of the material layer and having a smooth contour; the material layer and the opening. and a barrier metal film formed on the surface of the semiconductor substrate.

Furthermore, the method for manufacturing a Schottky barrier type semiconductor device according to the present invention includes a step of forming an insulating film on the surface of a semiconductor substrate of one conductivity type, and forming a material layer containing impurities of the opposite conductivity type on the insulating film. a step of patterning this material layer to form an opening; and a step of under-etching the insulating film using the material layer in which the opening has been formed as a mask to form an opening that is set back from the opening. forming a polycrystalline semiconductor film over the material layer and the exposed semiconductor substrate; and anisotropically etching the polycrystalline semiconductor film to form a smooth wall of the opening in the material layer. a step of 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 and the surface of the material layer surrounded by the sidewall.

In the above-mentioned Schottky barrier type semiconductor device of the present invention, since a smooth sidewall is formed on the wall of the opening, the barrier metal film also becomes smooth in this opening, eliminating the possibility of step breakage and providing a stable film. Forward voltage VF and breakdown voltage can be obtained. The guard ring formed on the surface of the semiconductor substrate is electrically connected to the material layer through the conductive sidewall, so the material layer acts as a field plate, resulting in higher breakdown voltage. At the same time, the device characteristics are stabilized and reliability is improved.

In addition, since the guard ring is formed in a self-aligned manner by diffusing impurities from a material layer such as a polycrystalline silicon film of opposite conductivity type onto the surface of the semiconductor substrate, the photo-etching process is reduced and the geometric dimension is reduced. Accuracy will also be improved, and there will be no need to provide a margin for alignment in the IC, allowing for miniaturization.

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

First, an n-type silicon substrate 2 containing a high concentration of n-type impurities is prepared.
1, the specific resistance is 1~2Ω-country, and the thickness is 6~10μ
FIG. 1 shows how an n-type semiconductor substrate with an n-on n' structure is formed by forming an n-type silicon epitaxial layer 22 of m.
Shown in a).

Next, on the n-type epitaxial layer 22, about 1,000 to 20
A silicon oxide film 23 having a thickness of about 3,000 to 4,000 wafers is formed thereon, and a polycrystalline silicon film 24 having a thickness of about 3,000 to 4,000 wafers is further 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 opening 24a is formed by selectively etching the °-type polycrystalline silicon film 24.

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. 1C, and has an opening 23a that is set back from the opening 24a of the p'-type polycrystalline silicon film 24.

Next, a polycrystalline silicon film 25 is applied to the entire surface, for example, 50%
Figure 1 (d) shows how the film is deposited to a thickness of 0.00 to 6000 people.
Shown below.

Subsequently, this polycrystalline silicon film 25 is subjected to anisotropic etching such as reactive ion etching to form sides having smooth contours on the walls of the opening 24a of the p-type polycrystalline silicon film 24. FIG. 1(e) shows how the wall 25a is formed. At this time, in order to prevent over-etching, a CVD-3iOz film may be formed on the surface of the p0 type polycrystalline silicon film 24. Also, Figure 1 (
In e), the surface of the n-type epitaxial layer 22 inside the opening is also slightly etched to form a recessed part, but this is not necessarily necessary, and only the polycrystalline silicon film on the n-type epitaxial layer is removed by etching. That's fine if you can.

Next, heat treatment is performed to diffuse p-type impurities into the surface of the n-type epitaxial layer 22 from the portion of the p-type polycrystalline silicon film 24 that extends inward from the oxide film 23, and
FIG. 1(f) shows how the guard ring 26 made of the ゛-type semiconductor layer is formed. At this time, the p-type impurity is also diffused into the n-type epitaxial layer 22 through the sidewall 25a made of polycrystalline silicon, and the guard ring 26 is extended to the bottom of the sidewall. The sidewall 25a also becomes conductive.

Next, Mo, Ni+Cr, PL+T are applied to the entire surface.
The barrier metal film 27 made of a high melting point metal such as
Deposited to a thickness of 00 to 5000 people, and then AI on top of it
Figure 1 shows how a Schottky barrier diode is completed by depositing a metal electrode film 28 with a thickness of about 5 to 10 μm and further forming an AI back electrode film 29 on the back surface of the n9 type silicon base +l121. Shown below. In addition, when manufacturing a barrier type IC, the thickness of the barrier metal film should be 500 Å or less, and the thickness of the AI metal electrode film should be 1.
~2 μm.

As described above, in the present invention, the p-type impurity doped into the polycrystalline silicon film 24 is transferred to the semiconductor substrate 21.22 through the space formed by under-etching the oxide film 23 and the sidewall 25a made of polycrystalline silicon. Since the guard ring 26 is formed by diffusing it on the surface, the guard ring can be accurately and easily formed in a self-aligned manner without increasing the number of photo-etching processes.

In addition, in the completed Schottky barrier diode, the guard ring 26 is a conductive sidewall 25a.
Since the p9 type polycrystalline silicon film 24 is electrically connected to the p° type polycrystalline silicon film 24 through the Trustworthiness will also be improved. Furthermore, since the sidewall 25a is formed by anisotropically etching the polycrystalline silicon film 25, its contour is smooth, and therefore the barrier metal film 27 formed thereon is also subjected to strong stress at the stepped portion. This means that no breakage or peeling occurs, and the forward voltage vF and breakdown voltage are stabilized.

FIG. 2 is a sectional view showing another embodiment of the Schottky barrier diode according to the present invention. In this example, the same parts as in the previous example are denoted by the same reference numerals, and detailed explanation thereof will be omitted. In this example, after forming a p° type polycrystalline silicon film 24, a CVD-3iOz film 30 is formed thereon. When such a CVD-5iOz film 30 is inserted between the p-type polycrystalline silicon film 24 and the polycrystalline silicon film for forming the sidewall 25a and anisotropic etching is performed, the oxide film 23 Since etching of the upper p'-type polycrystalline silicon film 24 is prevented, it becomes easy to perform sufficient etching to completely remove the polycrystalline silicon film 25 on the n-type epitaxial layer 22.

(Effects of the Invention) According to the present invention described above, the guard ring 26 formed along the opening on the surface of the semiconductor substrate 21, 22 is inserted through the side wall 25a formed on the wall of the opening. Since it is electrically connected to the p0-type polycrystalline silicon film 24, the p-type polycrystalline silicon film 24 acts as a field plate, and together with the MIGARD ring, an even higher breakdown voltage can be obtained. At the same time, device characteristics are stabilized and reliability is improved.

In addition, since the sidewall beams are formed by anisotropic etching such as active ion etching, their contours are smooth, and the M deposited on top of them is smooth.
The barrier metal film 27, such as 0, will not break or peel off, and a stable forward voltage V and breakdown voltage will be obtained.

Furthermore, in the method of the present invention, since the guard ring is formed by diffusion of impurities from the p-type polycrystalline silicon film 24, it can be formed accurately in a self-aligned manner without increasing the number of photo-etching steps, increasing productivity. It is possible to achieve a significant improvement in

Furthermore, an oxide film 2 formed on the surface of the semiconductor substrate 21 and 22
By controlling the amount of underetching in step 3, the length of the opening 23a and the opening 24a of the p9 type polycrystalline silicon film 24 above it, measured along the surface of the semiconductor substrate, can be adjusted. The width of the guard ring 26 can be adjusted as desired. Therefore, since narrow guard rings can be made accurately, it is possible to miniaturize integrated circuits. Furthermore, I.C.
Since there is no need to provide a margin for positioning, there is an advantage that miniaturization can be achieved.

FIG. 3 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.

[Brief explanation of the drawing]

FIGS. 1(a) to (phantom) are cross-sectional views showing the structure in the sequential steps of manufacturing a Schottky barrier diode according to the method of the present invention. FIG. 2 is a cross-sectional view showing another example of the Schottky barrier diode according to the present invention. Figures 3 and 4 are graphs showing the reverse voltage characteristics of a Schottky barrier diode made by the method of the present invention and a conventional Schottky barrier diode, and Figure 5 is the structure of a typical conventional Schottky barrier diode. 6(a) to (d+ are cross-sectional views for explaining a conventional method of manufacturing a Schottky barrier diode having a guard ring. 21...n-type silicon substrate 22. ...N-type epitaxial layer 23...Oxide film 23a...Opening 24
...p+ type polycrystalline silicon film 24a...opening 25...polycrystalline silicon film 25a...side wall 26...guard ring (p" type semiconductor layer) 27...
Barrier metal film 28.29...Metal electrode film 3O-
CVD-5ift membrane patent applicant TDC Co., Ltd. Figure 1 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. A semiconductor substrate of one conductivity type, an insulating film formed on the surface thereof and having an opening, and a semiconductor substrate formed on the insulating film and located inward from the opening of the insulating film. a material layer containing an impurity of an opposite conductivity type, and a semiconductor of an opposite conductivity type formed on the surface of the semiconductor substrate along the opening by diffusion of the impurity contained in the material layer; a guard ring configured by layers; a conductive sidewall formed on the wall of the opening in the material layer and having a smooth contour; and a barrier metal film formed on the surface of the material layer and the semiconductor substrate in the opening. A Schottky barrier type semiconductor device comprising: 2. The Schottky barrier type semiconductor device according to claim 1, wherein the material layer and the sidewall are made of polycrystalline silicon. 3. 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 an impurity of the opposite conductivity type on this insulating film, and a step of patterning this material layer to form an opening. a step of under-etching the insulating film using the material layer in which the opening has been formed as a mask to form an opening in the insulating film that is recessed from the opening; and the material layer and the exposed material layer. a step of forming a polycrystalline semiconductor film on the semiconductor substrate formed by the material layer; a step of anisotropically etching the polycrystalline semiconductor film to form a smooth sidewall on the wall of the opening of the material layer; , a step of 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, and a surface of the semiconductor substrate and a surface of the material layer surrounded by the sidewalls. 1. A method for manufacturing a Schottky barrier type semiconductor device, comprising the step of forming a barrier metal film thereon.