JPH01268167A - Manufacture of schottky diode - Google Patents

Abstract

PURPOSE:To restrict the superposition of a metal film and an annular layer to a necessary minimum limit and to rationalize a manufacture by reducing the number of photoetching times by performing a step of diffusing the annular layer after a step of forming a pattern of the metal film, and diffusing the annular layer with the metal film as a mask. CONSTITUTION:The surface of a semiconductor 1 is wholly covered with an oxide film as an insulating film 10, and a window 10a is formed by first photoetching. The whole surface is covered with a high melting point metal such as tungsten or the like to form a Schottky junction with the semiconductor 1, and a metal film 11 is insularly formed on the surface of the semiconductor 1 in the window 10a by second photoetching. Boron ions B are implanted as a p-type impurity by an ion implanting method from the exposed annular semiconductor surface to the surface of the semiconductor, the implanted boron 12a is diffused in a thermally diffusing step to form an annular layer 12. Thus, the layer 12 is effectively conductively brought into contact with the peripheral edge of the film 11. The layer 12 is provided thereby to prevent an electric field from concentrating at the peripheral edge of the film 11, and a breakdown strength value is provided at the formed Schottky diode.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a p-type annular structure that is in conductive contact with a metal film on the semiconductor surface near the bottom of the periphery of a metal film that makes a Schottky junction with an n-type semiconductor. The present invention relates to a method of manufacturing a Schottky diode formed by diffusing layers, or a method of manufacturing a semiconductor device incorporating this Schottky diode.

[Conventional technology]

As is well known, Schottky diodes have a very small forward voltage drop and are suitable for large currents. For improvement, it has been conventional practice to provide the above-mentioned annular layer or guard ring. FIG. 3 shows a cross section of such a conventional Schottky diode.

As shown in the figure, n-type silicon is used as the semiconductor 1, and a Schottky junction is formed between the surface of the semiconductor 1 and a metal film 4 made of various metals, which is usually called a barrier metal. The diode formed by this junction is used in a state where current flows from the metal film 4 to the semiconductor 1, but in a reverse bias state where a positive voltage is applied to the semiconductor 1, a voltage breakdown occurs at the periphery of the metal film 4. Since this tends to occur, an annular layer 2 is diffused on the surface of the semiconductor 1 below the periphery in a p-type, which is opposite to that of the semiconductor 1, as shown in the figure. The insulating film or oxide film 3 is, of course, for protecting the surface of the semiconductor 1.

In a Schottky diode having such a structure, the annular layer 3 has substantially the same potential as the metal film 4, so that the periphery of the metal film 40 is expanded into the annular layer 3, so that electric field concentration at the periphery is alleviated. The withstand voltage value is improved. When a high voltage is applied in the opposite direction, the depletion layer usually extends mainly towards the n-type semiconductor 1.

[Problem to be solved by the invention]

However, in such a conventional Schottky diode,
For manufacturing reasons, the area of the annular layer 2 becomes larger than necessary, resulting in a problem that the size of the diode tends to increase. The reason for this will be explained below.

In manufacturing the Schottky diode shown in Figure 3,
First, an oxide film (not shown) is deposited on the surface of the n-type semiconductor 1, a ring-shaped window is formed therein by first photo-etching, and the annular layer 2 is diffused in p-type using the windowed oxide film as a mask. Next, the oxide film 3 shown in the figure is applied, and a second photo-etching process is performed to cut out a window at the location where Schottky bonding with the metal film 4 is to be made. Furthermore, a predetermined metal for the metal film 4 is deposited on the entire surface, and the metal film 4 is patterned as shown in the figure by a third photo-etching process.

At this time, the problem is the accuracy in mask alignment between the first photoetching to determine the pattern of the annular layer 2 and the second photoetching to determine the contact surface between the metal film 40 and the semiconductor 1 or the annular layer 2. If this mask alignment deviates, there will be a portion of the periphery of the metal film 4 that is not covered by the annular layer 2, and the required withstand voltage value will not be obtained. For this reason, it is necessary to allow a considerable amount of overlap between the metal film 4 and the annular layer 2 as shown in the figure in anticipation of possible misalignment that may occur during mask alignment. The size of the diode becomes larger than necessary.

SUMMARY OF THE INVENTION An object of the present invention is to solve these conventional problems and provide a method for manufacturing a Schottky diode that can minimize the overlap between the metal film and the annular layer.

[Means to solve the problem]

According to the present invention, this purpose is achieved by diffusing a p-type annular layer in conductive contact with the metal film on the semiconductor surface near the bottom of the periphery of the metal film that forms a Schottky junction with the n-type semiconductor, as described at the beginning. A Schottky diode is manufactured by a process of coating the semiconductor surface with an insulating film that is impermeable to the metal for the metal film, cutting out a contour window that defines the outer edge of the annular layer, and forming a Schottky junction. A process of depositing a metal with a high melting point as a metal to form an island-shaped metal film inside an insulating film window, and a ring-shaped semiconductor between the periphery of the island-shaped metal film and the outline of the insulating film window. This is achieved by manufacturing through a step of diffusing p-type impurities from the surface to form an annular layer on the semiconductor surface.

[Effect]

As can be seen from the above structure, the present invention performs the annular layer diffusion step after the metal film patterning step, contrary to the conventional method,
By diffusing the annular layer using the metal film as a mask, we succeeded in suppressing the overlap between the two to the necessary minimum. However, if the annular layer is diffused after the metal film is formed, the metal film will be exposed to high temperatures during diffusion. Use high melting point metals such as

When diffusing the annular layer using such a metal film as a mask, as is well known, impurities not only diffuse in the direction perpendicular to the surface of the semiconductor, but also diffuse in the direction along the surface and even under the metal film. However, since a semiconductor with a relatively low impurity concentration is used for the Schottky diode, this wrap-around is easy, and a good overlapping portion is formed between the metal film and the annular layer. Of course, the degree of this overlap can be controlled by selecting the diffusion depth of the annular layer, and the required withstand voltage value can usually be obtained with a depth of about 1 μm. This eliminates the need for a margin of at least a few microns that was conventionally necessary to ensure this overlap.

Note that the photo-etching required in the manufacturing method of the present invention is performed twice: opening the window in the insulating film and forming the pattern on the metal film.The number of photo-etching steps is reduced by one from the three times in the conventional method, and the shot-etching according to the present invention is performed. It is also possible to streamline the production of key diodes.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings. 1st
The figure shows the main steps of the method for manufacturing a Schottky diode according to the present invention.

In the same figure (a), the semiconductor 1 has a specific resistance of 1, for example.
An oxide film is entirely deposited on the surface of an n-type silicon substrate or an epitaxial layer of about 0.00 nm by, for example, steam oxidation as an insulating film 1o, and then a window 10a is cut out by the first photoetching. When an oxide film is used as the insulating film 10 as in this example, it is necessary to prevent the semiconductor surface under the insulating film from being contaminated by the metal when a metal film is deposited thereon in the next step. Thickness 0
．． It is desirable to have a thickness of 3μ or more to ensure sufficient impermeability to metals. Moreover, the window 10a has the same (b)
) In addition to exposing the semiconductor surface to form the metal film 11 shown in (d), its outline will be diffused in a later process.
This is to limit the outer edge of the annular layer 12 shown in ).

Figures 1 and 2) show the process of forming a metal film 11, in which the above-mentioned high melting point metal such as tungsten, molybdenum, titanium, tantalum, etc. is deposited to form a Schottky junction with the semiconductor 1 by sputtering or the like to a thickness of 0.5 to 1 μm. After coating the entire surface to a thickness of
1 is formed in the shape of an island as shown in the figure on the surface of the semiconductor 1 inside the window 10a. Although a chemical etching method can be used for this etching, a so-called dry etching method is more suitable. The annular semiconductor surface remaining between the metal film 11 and the insulating film 10 after the formation of this metal film does not need to be particularly wide; rather, this residual surface is caused by errors in mask alignment during the second photo-etching described above. The size of the window 10a cut out in the insulating film 10 is determined in advance so as to at least avoid the occurrence of the gap.
When estimated, a ring-shaped semiconductor surface with an average width of just over 51 meters will remain.

Figures (C) and (d) show the process of diffusing the annular layer 12 from the exposed annular semiconductor surface. For example, boron ion B is 1xlO” atom/c
After introducing the introduced boron 12a onto the semiconductor surface at a dose of around II1, the introduced boron 12a is heated at 1000 to 1100°C for 230 minutes to 1 hour in the thermal diffusion process shown in FIG. 7 atoms/d, and usually II! The annular layer 12 is created by diffusing to a depth of about m.

At this time, since the impurity 12a also diffuses in the direction along the semiconductor surface, the annular layer 12 sinks into the lower side of the metal film 11 by about 1 μm, which is approximately the same diffusion depth as shown in the figure. is in reliable conductive contact with the peripheral edge of the metal film 11. Note that, at this time, the annular layer 12 slightly sinks under the insulating film 10 as shown in the figure, but this does not particularly affect the performance of the Schottky diode. As can be seen from the figure, the provision of this annular layer 12 prevents electric field concentration at the periphery of the metal film 11, and when the diffusion depth of the annular layer 12 is set to about 1 μm as described above, 30 to the Schottky diode made by
It can have a withstand voltage value of about V.

As will be seen, in the present invention, if the diffusion depth of the annular layer is increased in order to make the Schottky diode high withstand voltage, the overlap with the metal film will increase accordingly, resulting in the electric field at the periphery of the metal film. The protection against concentration is simultaneously strengthened. However, of course, the degree of this overlap is much smaller than in the prior art, and the present invention can reduce the area of the semiconductor chip required to fabricate the Schottky diode by that much.

In addition, in the method of the present invention, when the metal film is formed, a Schottky junction is formed between it and the semiconductor, and this junction is subjected to high temperature during thermal diffusion of the annular layer.
It has been confirmed through experiments and the like that there is no concern that the previously formed Schottky junction will be adversely affected at this time.

FIG. 2 shows an example of incorporating a Schottky diode D into a bipolar transistor T according to the method of the invention. As shown in FIG. 5A, a Schottky diode D comprising a metal film 11 and an annular layer 12 is first fabricated on the surface of a semiconductor I by the method of the present invention described above.
At this time, the annular layer 12 is diffused to a depth of about 2 μm, which is deeper than the previous example, and its left side is diffused widely as shown in the figure, and this left side is used as a p-type base layer. Then, an npn type bipolar transistor T is fabricated using the semiconductor 1 as an n type collector region. For this purpose, after depositing the oxide film 13 on the entire surface, the emitter layer 14 and the collector connection layer 15 are each made of an n-type layer with a thickness of, for example, 1.5 simultaneously diffuse to a depth of . Further, electrode films 15 made of aluminum or the like are provided at required locations as shown in the figure, and the base B,
Connect the terminals for emitter E and collector C to transistor T.
Each is derived for each purpose.

FIG. 2B shows an equivalent circuit of a bipolar transistor T incorporating this Schottky diode D. As shown, the Schottky diode D is connected between the collector C and the base B of the transistor T in a reverse direction. The Schottky diode D incorporated in this way is connected to the transistor T as is well known.
It is very useful for improving the operating speed of logic gates or logic circuits using the MOS transistor, especially the operating speed when the logic gate is turned off.

The Schottky diode according to the method of the present invention can be incorporated into integrated circuits, etc. in various ways, and its capabilities,
Its structure is not limited to the above-described embodiments, but can be implemented in various ways within the scope of the present invention.

[Effects of the Invention] As explained above, a p-type annular layer that is in conductive contact with the metal film is diffused into the semiconductor surface near the bottom of the periphery of the metal film that makes a Schottky junction with the n-type semiconductor described at the beginning. A Schottky diode is manufactured by a process of coating the semiconductor surface with an insulating film that is impermeable to the metal for the metal film, cutting out a contour window that defines the outer edge of the annular layer, and forming a Schottky junction. A process of depositing a metal with a high melting point as a metal to form an island-shaped metal film inside an insulating film window, and a ring-shaped semiconductor between the periphery of the island-shaped metal film and the outline of the insulating film window. In the method of the present invention, the metal film is first formed on the semiconductor and then the annular layer is formed on the semiconductor surface. The annular layer is diffused using this as a mask, and as a result, the overlapping area between the metal film and the annular layer is reduced compared to the conventional method, and the Schottky diode can be made smaller by that amount. This advantage is particularly important when incorporating a Schottky diode into an integrated circuit device, either as an attachment to a transistor or the like, or as a stand-alone device.The present invention reduces the area of the semiconductor chip required for incorporating the Schottky diode. The degree of integration can be increased. Furthermore, as can be seen from the description of the embodiments, the method of the present invention can reduce the number of photo-etching steps required when manufacturing a Schottky diode from the conventional three times to two times, thereby reducing manufacturing costs.

In this way, the method of the present invention can be applied to integrated circuit devices, etc.
This has the remarkable effect of reducing the chip area and reducing the number of manufacturing steps, thereby significantly streamlining the manufacturing process.

[Brief explanation of the drawing]

1 and 2 relate to the present invention, FIG. 1 is a cross-sectional view showing an example of a Schottky diode manufactured by the method of the present invention in each main process, and FIG. 2 is a Schottky diode according to the present invention. FIG. 2 is a cross-sectional view and an equivalent circuit diagram showing an example in which the device is incorporated into a bipolar transistor. FIG. 3 is a cross-sectional view of a Schottky diode manufactured by a conventional method. In the figure, 1: semiconductor, 2: annular layer, 3: oxide film, 4: metal film, 1
0: Insulating film or oxide film, 10a: Window, 11: Metal film, 12: Annular layer, 12a: Impurity introduced for the annular layer, 13: Oxide film, 14: Emitter layer, 15: Collector connection layer, 16 : electrode film, B: base, C: collector, D nitrogen diode, E: emitter, T: bipolar transistor.

Claims (1)

[Claims] A method for manufacturing a Schottky diode in which a p-type annular layer in conductive contact with a metal film is diffused into a semiconductor surface near the bottom edge of a metal film that makes a Schottky junction with an n-type semiconductor, the method comprising: The process of applying an insulating film that is impermeable to the metal for the metal film on the surface and cutting out a window to define the outer edge of the annular layer, and applying a metal with a high melting point as the metal for the Schottky junction. a step of forming an island-shaped metal film inside the window of the insulating film, and diffusing p-type impurities from the annular semiconductor surface between the periphery of the island-shaped metal film and the outline of the window of the insulating film. 1. A method for manufacturing a Schottky diode, comprising the step of: forming an annular layer on a semiconductor surface portion.