JP2010225914A - Schottky barrier diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a Schottky barrier diode deteriorates in diode characteristics and so on owing to mechanical damage due to a load and ultrasonic vibration when wire bonding to an anode electrode of the Schottky barrier diode is carried out. <P>SOLUTION: An insulating film having an opening is provided below a region of the Schottky barrier diode where at least an external connection means is fixed, to form a Schottky metal layer, and the diode characteristics are prevented from deteriorating owing to the mechanical damage when the anode electrode made of, for example, aluminum and an aluminum wire are connected to each other. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a Schottky barrier diode, and more particularly to a Schottky barrier diode that prevents deterioration of diode characteristics when an external connection means such as wire bonding is fixed.

  A Schottky barrier diode is a semiconductor element that utilizes the rectifying action of a Schottky barrier formed when a predetermined metal layer is brought into contact with a semiconductor layer. It has a characteristic that it can operate at a higher speed than a general PN junction diode and has a small forward voltage drop.

  When a negative voltage is applied to the N-type semiconductor substrate 1 side of the Schottky barrier diode and a positive voltage is applied to the metal layer 13 side of the n− epitaxial layer 2, a current flows. This is referred to as a directional voltage VF. On the other hand, when a positive voltage is applied to the opposite direction, that is, to the n-type semiconductor substrate 1 side and to the metal layer 13 side, almost no current flows. The leakage current at this time is referred to as reverse leakage current IR, and the voltage is referred to as reverse voltage VR.

  FIG. 4 shows a conventional Schottky barrier diode 200. 4A is a plan view, and FIG. 4B is a cross-sectional view taken along the line bb of FIG. 4A. In the plan view, the Schottky metal layer 6, the anode electrode 7, and the insulating film 5 are omitted.

  The substrate is obtained by stacking an n− type semiconductor layer 2 on an n + type semiconductor substrate 1 by, for example, epitaxial growth. A metal layer 6 forming a Schottky junction is provided on the surface of the n − type epitaxial layer 2. The Schottky metal layer 6 is, for example, molybdenum (Mo), and a region where the Schottky metal layer 6 and the n − type epitaxial layer 2 are in contact becomes a Schottky junction region.

  In the outermost periphery of the Schottky junction region, a guard ring region 4 in which p + -type impurities are diffused is provided in order to ensure a predetermined breakdown voltage, and a part thereof contacts the Schottky metal layer 6.

  An anode electrode 7 made of aluminum (Al) is provided so as to cover the entire surface of the Schottky metal layer 6, and a cathode electrode 8 is provided on the back surface of the substrate (see, for example, Patent Document 1). Reference numeral 5 denotes an insulating film such as a Si oxide film. For example, an aluminum wire 9 is connected to the anode electrode 7 made of aluminum as external connection means.

JP-A-6-224410 (Page 2, Fig. 2)

  An aluminum wire of 25 to 400 μmφ is mainly used as a metal wire for ultrasonic wire bonding. The joint with the bonding pad is about 1.5 to 2 times the diameter of the metal wire used. In ultrasonic wire bonding, metal wires are bonded using the energy of load and ultrasonic vibration. The joining method is generally performed by wedge bonding. The aluminum wire passed through the hole at the tip of the wedge tool is pressed by a load at the bond point and joined by ultrasonic vibration. Since the bonding pad aluminum and the wire aluminum are joined together, no intermetallic compound is formed, and since there is no change over time, it is highly reliable and is mainly applied to semiconductor products that require high reliability.

  However, the load at the time of bonding the aluminum wire to the bonding pad and the mechanical damage due to ultrasonic vibration affect the Schottky junction of the Schottky barrier diode, and the diode characteristics, particularly the reverse voltage VR is lowered. Had occurred.

  The present invention has been made in view of such a problem, and is a one-conductivity-type semiconductor substrate, a one-conductivity-type semiconductor layer provided on the semiconductor substrate, an insulating film provided on one main surface of the one-conductivity-type semiconductor layer, A second opening provided in the insulating film and exposing the one-conductivity-type semiconductor layer; and a second opening provided on the insulating film and in Schottky junction with the one-conductivity-type semiconductor layer through the second opening. 1 metal layer, a second metal layer provided on the first metal layer, and external connection means fixed on the second metal layer, and at least a region for fixing the external connection means The problem is solved by having the insulating film having the second opening below.

  According to the present embodiment, first, an insulating film having an opening is provided below at least a region where the external connection means is fixed to form a Schottky metal layer, and the n − type semiconductor layer and the shot are formed through the opening of the insulating film. By forming a Schottky junction with the key metal layer, it is possible to prevent deterioration of diode characteristics due to mechanical damage at the time of joining an anode electrode made of, for example, aluminum and, for example, an aluminum wire.

  Second, a conventional Schottky junction can be formed between an n− type semiconductor layer and a Schottky metal layer via an insulating film having an opening by simply changing the mask of the insulating film. It is possible to prevent deterioration of the diode characteristics due to mechanical damage during wire bonding without increasing.

It is (A) top view, (B) top view, (C) sectional drawing for demonstrating the Schottky barrier diode of this embodiment. It is a plane schematic diagram for demonstrating the Schottky barrier diode of this embodiment. It is sectional drawing for demonstrating the manufacturing method of the Schottky barrier diode of this embodiment. It is (A) top view and (B) sectional drawing for demonstrating the conventional Schottky barrier diode.

  The embodiment of the present invention will be described in detail with reference to FIGS. 1 to 3 by taking as an example a Schottky barrier diode in which an aluminum wire is connected as an external connection means to an aluminum anode electrode.

  FIG. 1 shows a Schottky barrier diode of this embodiment. 1A and 1B are plan views of one main surface of the Schottky barrier diode 100, and FIG. 1C is a cross-sectional view taken along line aa in FIGS. FIG. 1A is a diagram in which the metal layer on the surface of the Schottky barrier diode is omitted, and FIG. 1B is a diagram illustrating a pattern of the metal layer and the insulating film.

  The Schottky barrier diode of the present invention includes a one-conductivity-type semiconductor substrate 1, a one-conductivity-type semiconductor layer 2, an insulating film 5, a first opening OP1, a second opening OP2, and a first metal layer 6. The second metal layer 7 and the external connection means 9 are included.

  Referring to FIGS. 1A and 1C, a substrate SB is formed by laminating an n− type semiconductor layer 2 on a high concentration one conductivity type (hereinafter n + type) silicon semiconductor substrate 1. The n − type semiconductor layer 2 is, for example, an epitaxial layer.

  A p-type (p + type) semiconductor region 4 is provided in a ring shape on the outer periphery of the substrate SB. The p + type semiconductor region 4 is a guard ring 4 provided to ensure a withstand voltage when a reverse voltage is applied to the Schottky barrier diode 100. The guard ring 4 is a region where polysilicon doped with high-concentration p-type impurities is buried in the trench, or a region where high-concentration p-type impurities are diffused in the n − -type semiconductor layer 2. In the present embodiment, the region inside the guard ring 4 is referred to as an operation region OR as a region mainly functioning as the Schottky barrier diode 100.

  Referring to FIG. 1C, an insulating film 5 having a thickness of, for example, about 0.4 μm to 1.0 μm is provided on one main surface of the substrate SB (n− type semiconductor layer 2). The insulating film 5 is, for example, an oxide film having a plurality of openings OP. The openings OP are all provided in the operation region OR in the pattern of one main surface shown in FIG. 1A, and the first opening OP1 located near the end of the operation region OR, and the first opening OP1. The second opening portion OP2 is disposed inside.

  The first opening OP1 is provided in one continuous ring shape so that a part of the n − type semiconductor layer 2 and the guard ring 4 on the outermost periphery of the operation region OR is exposed.

  The second opening OP2 is provided inside the first opening OP1. A large number of second openings OP2 are formed, for example, in a hexagonal shape so that the n − type semiconductor layer 2 is exposed. The opening width is, for example, about 5 to 10 μm, and the distance between the openings is, for example, about 5 to 10 μm, but is appropriately selected according to the chip size and the type / size of the external connection means.

  1B and 1C, the first metal layer 6 is provided on the insulating film 5, and is in contact with the n − type semiconductor layer 2 through the first opening OP1 and the second opening OP2. To do. The first metal layer 6 is, for example, a molybdenum (Mo) layer, and forms a Schottky junction with the n − type semiconductor layer 2 exposed from the first opening OP1 and the second opening OP2, respectively.

  The second metal layer 7 is provided on the first metal layer 6 and is formed of a laminated metal layer such as titanium (Ti) / nickel (Ni) / aluminum (Al), for example, and the anode electrode A of the Schottky barrier diode 100 and Become.

  On the other main surface (the surface of the n + type silicon semiconductor substrate 1) of the substrate SB, a metal layer 8 that becomes the cathode electrode CA of the Schottky barrier diode 100 is provided.

  An aluminum wire 9 as an external connection means is fixed to the anode electrode A. The aluminum wire diameter is, for example, about 25 to 400 μmφ. An ultrasonic method is used for wire bonding of the aluminum wire 9. In ultrasonic wire bonding, the metal wire is bonded using the energy of the load and ultrasonic vibration, so the load and ultrasonic vibration are applied to the bond point, and mechanical damage causes Schottky barrier diode Schottky. Conventionally, problems such as a reduction in diode characteristics, in particular, reverse voltage VR, have occurred.

  However, in the embodiment of the present invention, the insulating film 5 having the second opening OP2 is provided at least below the region where the aluminum wire 9 is fixed, the first metal layer is formed, and the second opening of the insulating film 5 is formed. By forming a Schottky junction between the n − type semiconductor layer 2 and the first metal layer 6 through OP 2, the diode characteristics are deteriorated due to mechanical damage when the anode electrode 7 made of aluminum and the aluminum wire 9 are joined. Can be prevented. This is because the oxide film 5 is much harder than a metal such as aluminum and has high resistance to mechanical stress during wire bonding.

  FIG. 2 is an example of a pattern of the second opening OP2 of the insulating film 5, and is a schematic plan view in which only the portion of the insulating film 5 in FIG. 1A is extracted.

  In FIG. 1 (A), the second opening OP2 has a large number of hexagons arranged as a shape. However, as shown in FIG. 2 (A), the insulating film 5 is arranged in a circular pattern so that the portions are in a lattice shape. Alternatively, as shown in FIG. 2B, the circles may be arranged alternately. As shown in FIG. 2C, quadrangles may be arranged so that the portions of the insulating film 5 have a lattice shape, or quadrangles may be arranged alternately as shown in FIG. Alternatively, the stripe-shaped second openings OP2 may be arranged as shown in FIG. Needless to say, the shape of the second opening OP2 is not limited to that shown in the figure, and if the insulating film 5 is not extremely sparse, it can withstand mechanical stress during wire bonding.

  If the chip size is small and the area of the operation region OR and the area necessary for fixing the external connection means to the second metal layer are not so different, there is no first opening OP1 and the entire operation region OR is covered. Thus, the second opening OP2 may be provided in the insulating film 5. However, if the area of the operation region OR is sufficiently larger than the area necessary for fixing the external connection means to the second metal layer, the first opening OP1 is provided, and the n − type semiconductor layer 2 and the first metal layer 6 are formed. It is preferable to increase the Schottky junction area between them and improve the diode characteristics of the Schottky barrier diode.

  Next, a method for manufacturing the Schottky barrier diode of the present invention will be described with reference to FIG.

  First step (FIG. 3A): A substrate SB in which an n− type semiconductor layer 2 is laminated on an n + type semiconductor substrate 1 is prepared, and an insulating film 5 such as an oxide film (thickness is 0.4 μm to 1.0 μm, for example). Degree).

  Second step (FIG. 3B): The insulating film 5 is etched with a desired pattern to form the first opening OP1, and the second opening OP2. The first opening OP1 is formed in one ring shape at the end of the operation region. A plurality of second openings OP2 are formed at a predetermined distance inside the first opening OP1. The second opening OP2 has, for example, a regular hexagonal shape, the opening width is, for example, about 5 to 10 μm, and the openings are separated by, for example, about 5 to 10 μm. However, the opening width and the distance between the openings are not limited to this, and are appropriately selected according to the chip size and the type / size of the external connection means.

  Third step (FIG. 3C): A first metal layer 6 of, for example, molybdenum (Mo), for example, is formed on one main surface of the substrate SB, for example, about 500 mm, and the first opening OP1 and the second opening OP2 respectively. A Schottky junction is formed with the exposed n − type semiconductor layer 2. Further, a second metal layer 7 made of a laminated metal layer such as titanium (Ti, for example, about 500 mm) / nickel (Ni, for example, about 1000 mm) / aluminum (Al, for example, about 3 μm) is formed on the first metal layer 6. The anode electrode A of the Schottky barrier diode. On the other main surface (the surface of the n + type silicon semiconductor substrate 1) of the substrate SB, a metal layer 8 to be the cathode electrode CA of the Schottky barrier diode 100 is formed. Next, an aluminum wire 9 of about 25 to 400 μmφ, for example, is fixed to the aluminum anode electrode A by ultrasonic wire bonding.

  In the embodiment of the present invention, the insulating film 5 having the second opening OP2 is provided at least below the region to which the aluminum wire 9 is fixed, and due to mechanical damage at the time of joining the anode electrode 7 made of aluminum and the aluminum wire 9 Degradation of the diode characteristics can be prevented. Compared to the conventional method (see FIG. 4), the number of steps does not increase because only the mask for etching the insulating film 5 in the second step (see FIG. 3B) is changed.

  In the embodiment of the present invention, the anode electrode 7 made of aluminum and the aluminum wire 9 have been described as examples. However, the present invention is not limited to this. For example, the gold wire 9 is used as an external connection means on the anode electrode 7 made of aluminum. Also in the case of fixing, ultrasonic bonding method wire bonding is used, and since the Schottky bonding is affected by ultrasonic strength and pressure bonding strength, the second opening OP2 is provided at least below the fixing region of the gold wire 9. Providing the insulating film 5 is effective in increasing the mechanical strength during wire bonding.

  Further, although not shown, when a metal plate is used as an external connection means, the diode characteristics are deteriorated due to the stress applied to the metal plate by providing an insulating film having an opening at least below the region where the metal plate is fixed. Can be prevented.

1 n + type silicon semiconductor substrate 2 n− type semiconductor layer 4 guard ring 5 insulating film 6 first metal layer 7 second metal layer (anode electrode)
8 Metal layer (cathode electrode)
9 External connection means 100, 200 Schottky barrier diode SB semiconductor substrate OR operation area OP1 first opening OP2 second opening

Claims (4)

One conductivity type semiconductor substrate;
A one conductivity type semiconductor layer provided on the one conductivity type semiconductor substrate;
An insulating film provided on one main surface of the one conductivity type semiconductor layer;
A second opening provided in the insulating film and exposing the one conductivity type semiconductor layer;
A first metal layer provided on the insulating film and in Schottky junction with the one conductivity type semiconductor layer through the second opening;
A second metal layer provided on the first metal layer;
External connection means secured on the second metal layer;
A Schottky barrier diode comprising the insulating film having the second opening below at least a region to which the external connection means is fixed.   The Schottky barrier diode according to claim 1, wherein the second opening includes a plurality of openings.   The first opening is provided around the second opening, and the first metal layer is in Schottky junction with the one-conductivity-type semiconductor layer through the first opening. The Schottky barrier diode described.   4. The Schottky barrier diode according to claim 3, wherein the second metal layer is aluminum and the external connection means is an aluminum wire.

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