JP3588256B2 - Schottky barrier diode - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a Schottky Barrier Diode (hereinafter, referred to as SBD), and more particularly, to an SBD element that can obtain a larger current capacity in the same area.
[0002]
[Prior art]
The SBD is a semiconductor element using a Schottky barrier formed when a predetermined metal layer is brought into contact with a semiconductor layer. It has characteristics of higher speed and smaller forward voltage drop than general PN junction diodes (for example, Japanese Patent Application Laid-Open No. 5-152562).
[0003]
Referring to FIG. 4, in the conventional SBD, an N- type epitaxial layer 2 is formed on an N + type semiconductor substrate 1, and a silicon oxide film 3 on the epitaxial layer 2 is opened to expose the silicon surface. And the barrier metal layer 4 is brought into contact with the exposed silicon surface. In addition, an annular P + guard ring region 5 is formed on the surface of the N− type epitaxial layer 2, and the barrier metal layer 3 is covered with an aluminum electrode 6.
[0004]
In manufacturing a semiconductor device, nickel (Ni), titanium (Ti), and molybdenum (Mo) are suitable materials for the barrier metal layer 4. Since each has a unique work function ΦB, most of the SBD characteristics (forward voltage VF, reverse current IR) can be determined by selecting a suitable metal as the barrier metal layer 4. The diode characteristics of the SBD element are determined by factors such as the impurity concentration of the epitaxial layer 2 and the area of the Schottky contact surface.
[0005]
[Problems to be solved by the invention]
Due to the recent trend toward lower power consumption, it is particularly desired that the forward voltage VF be reduced for SBD elements. As a method of reducing the forward voltage VF, there is a method of changing the barrier metal layer 4 to titanium (Ti) having a small work function ΦB, a method of increasing the impurity concentration of the epitaxial layer 2, and the like. If a large current can be passed, it means that the forward current VF is equivalently reduced. Therefore, it can be said that increasing the Schottky contact area is also an effective means. However, increasing the contact area, that is, increasing the chip area, has the disadvantage of immediately increasing costs.
[0006]
When titanium (Ti) having a small work function ΦB is used, for example, the forward voltage (VF) when nickel (Ni) is used is 0.3 to 0.35 V when the forward current IF is 100 mA. On the other hand, when titanium (Ti) is used, this value can be significantly reduced to 0.2 to 0.25 V at the same current value. However, there is a trade-off relationship between the forward voltage VF and the reverse current IR, and selecting a metal capable of reducing the forward voltage VF means increasing the reverse current IR (leakage current). . Therefore, the SBD element using the Ti barrier has a large leak current, which may result in an increase in power consumption due to the leak current. Molybdenum (Mo) is the most suitable as the barrier metal capable of minimizing the leak current, but the forward voltage VF increases to almost twice that of Ti. Therefore, there has been a demand for element characteristics that allow both the forward voltage VF and the reverse current IR.
[0007]
Further, since the limitation of the barrier metal layer 4 is to use only one type of work function ΦB, the range in which the VF-IF characteristic (forward voltage-forward current) can be controlled is narrow, so that the circuit In order to cope with all the required specifications, process development must be performed by the number of requirements, which has the disadvantage that the development period is lengthened and the cost is increased.
[0008]
[Means for Solving the Problems]
The present invention has been made in view of such a conventional problem, and in a Schottky barrier diode in which a metal layer forming a Schottky barrier is provided on the surface of a silicon layer and the surface of the metal is covered with an electrode material,
A first barrier metal layer provided with a plurality of trench grooves on a surface of the silicon layer and in contact with silicon including a side wall of the trench grooves to form a first Schottky barrier;
A second barrier metal layer overlying the first barrier metal layer and forming a second Schottky contact at the surface of the epitaxial layer between the trenches. Is what you do.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0010]
FIG. 1 is a sectional view showing an SBD according to the present invention. An N− type epitaxial layer 12 is formed on a N + type silicon semiconductor substrate 11 by vapor phase epitaxy, and an opening 14 is formed in a silicon oxide film 13 covering the surface of the epitaxial layer 12. An annular P + type guard ring region 15 is formed on the surface of the epitaxial layer 12 near the peripheral end, and a trench 16 having, for example, a width of 1.0 μm and a depth of 1.0 μm is formed on the surface of the epitaxial layer 12 exposed at the opening 14. Then, for example, a titanium (Ti) layer is formed as a first barrier metal layer 17 inside the trench groove 16 so as to bury the trench groove 16, and covers the first barrier layer 17 to contact the silicon surface of the opening 14. The second barrier metal layer 18 is formed, and an aluminum electrode 19 is formed so as to cover the second barrier metal layer 18.
[0011]
The many trench grooves 16 formed in the opening 14 are formed by shaving the silicon surface by anisotropic etching. For example, a lattice shape or an island shape having a width of 1.0 μ and a depth of 1.0 μ is provided. Is formed. The first barrier metal layer 16 is formed so as to bury the trench 16, and forms a first Schottky barrier in contact with silicon on the side and bottom surfaces of the trench 16. The second barrier metal layer 17 covers the top of the first barrier metal layer 16 and contacts the flat silicon surface of the surface of the opening 14 sandwiched between the trenches 16. To form a Schottky barrier.
[0012]
In this example, the area of the opening 14 and the width and depth of the trench 16 are designed so that the area ratio between the first Schottky barrier and the second Schottky barrier is about 50:50. . The aluminum electrode 19 serves as an extraction electrode on the anode side of the SBD, and has a structure in which the back surface of the substrate 11 is used as an extraction electrode on the cathode side. Since the titanium layer and the nickel layer are metal-metal junctions, this diode is equivalent to a configuration in which a diode using titanium as a barrier metal and a diode using nickel as a barrier metal are connected in parallel.
[0013]
With such a configuration, the area of the side wall of the trench 16 can also be used as the area for forming the first Schottky barrier, so that the area can be substantially increased while having the same chip size. In the above example, the contact area can be increased by 20 to 40% by the trench groove 16 with the opening 14 (excluding the guard ring region 15) being the same. Therefore, the forward voltage VF when a certain forward current IF flows can be reduced.
[0014]
In addition, in the present application, since a Schottky contact is formed between Ti and Ni at an area ratio of 50:50, it is possible to obtain an SBD characteristic that is substantially intermediate between the Ti barrier and the Ni barrier. That is, a lower forward voltage VF is obtained than that of the Ni barrier alone, and a smaller reverse current IR is obtained than that of the Ti barrier alone. These characteristics can be appropriately controlled by the area ratio between the Ti barrier (first Schottky barrier) and the Ni barrier (second Schottky barrier). Increasing the area of the first Schottky contact approximates the characteristic curve of the Ti barrier alone, and increasing the area of the second Schottky contact approximates the characteristic curve of the Ni barrier alone.
[0015]
2 and 3 are cross-sectional views for explaining an example of the manufacturing method.
[0016]
First, referring to FIG. 2A, an N + type semiconductor substrate 11 on which an epitaxial layer 12 having a specific resistance ρ of 0.5 to 1.0 Ω · cm and a thickness of 2 to 10 μm is prepared, and selectively diffused. An annular P + guard ring region 15 is formed on the surface of the epitaxial layer 12.
[0017]
Referring to FIG. 2B, an oxide film covering the surface of epitaxial layer 12 is removed to form opening 14.
[0018]
Referring to FIG. 2C, a photoresist mask is formed in opening 14 and silicon is etched by an anisotropic dry etching technique to form trench groove 16 having a predetermined width and depth.
[0019]
Referring to FIG. 2D, titanium having a thickness of about 0.5 μm is deposited as a first barrier metal layer 17 on the entire surface by a CVD method, and this is removed by etch back or photoetching to form trench trench 16. A first barrier metal layer 17 to be buried is formed. The essence of the present invention is not impaired even if the thickness of the titanium layer is further reduced and the titanium layer is covered along the shape of the trench 16.
[0020]
Referring to FIG. 3 (A), a nickel layer having a thickness of 300 to 2000 ° is deposited by sputtering deposition in opening 14 in which trench 16 has been formed, and the deposited nickel layer is patterned by a known photoetching method. Then, a second barrier metal layer 18 is formed.
[0021]
Referring to FIG. 3B, an aluminum layer having a thickness of 1.0 to 3.0 μ is deposited again by the sputter deposition method, and the second barrier metal layer 17 is covered by photoetching and a pad for external connection is formed. The structure shown in FIG. 1 is obtained by forming the constituting aluminum layer 19.
[0022]
In the above-described embodiment, the combination of Ti and Ni has been described. However, it is needless to say that the combination of Mo and other barrier metals or the combination of three or more types can be used.
[0023]
【The invention's effect】
As described above, according to the present invention, the provision of the trench 16 in the opening 14 can increase the first Schottky contact area between the first barrier metal layer 17 and silicon. Accordingly, when the openings 14 have the same area, a large amount of the forward current IF can flow even with the same forward voltage VF, and as a result, an SBD device with a small forward voltage VF can be obtained. Has advantages. Further, since the area of the opening 14 is not increased, an element having a larger current capacity can be obtained without increasing the pellet size.
[0024]
Furthermore, since a plurality of types of barrier metal layers having different barrier heights ΦB are used and the VF-IF and VR-IR characteristics can be controlled by their contact area, SBD devices with various characteristics can be realized only by changing the pattern. Have the advantages that can be. This makes it possible to provide an element whose forward voltage VF and reverse current IR are optimal in terms of circuit requirements.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for explaining the present invention.
FIG. 2 is a cross-sectional view for explaining a manufacturing method.
FIG. 3 is a cross-sectional view for explaining a manufacturing method.
FIG. 4 is a cross-sectional view for explaining a conventional example.

Claims (2)

In a Schottky barrier diode in which a barrier metal layer that forms a Schottky barrier with the silicon layer is provided on the surface of the one conductivity type silicon layer, and the metal layer is covered with an electrode material,
A plurality of trench grooves provided on the surface of the silicon layer,
A first buried in the trench groove, the surface being flush with the silicon surface between the trench grooves, contacting the silicon layer at a sidewall and a bottom surface of the trench groove to form a first Schottky barrier; A barrier metal layer;
A second barrier metal layer provided on the silicon layer and a flat surface on the first barrier metal layer and forming a second Schottky barrier on the surface of the silicon layer between the trenches; A Schottky barrier diode, comprising: The Schottky barrier diode according to claim 1, wherein the first barrier metal layer is titanium.

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