JPH08116072A - Schottky barrier semiconductor device - Google Patents

Abstract

PURPOSE: To provide a Schottky barrier diode which maintains a small backward leak current and decreases a forward threshold voltage. CONSTITUTION: A lot of protrusions 4 whose sections are nearly trapezoidal are formed stripe-wise on the upper surface of a semiconductor substrate 2. First Schottky metal films 8 of low barrier height are formed on the flat top surfaces 5 of the protrusions 4. A second Schottky metal film 9 is formed from the first Schottky metal films 8 to the whole part of the upper surface of the semiconductor substrate 2, and a Schottky electrode 10 is formed. A depletion layer due to the first Schottky metal films is vanished by an applied voltage in the forward direction, and the path of a current flowing from the first Schottky metal films to an ohmic electrode is ensured. A depletion layer due to the second Schottky electrode film is spread on the whole part of the Schottky electrode, and the current path is cut off, so that the withstand voltage in the backward direction increases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Schottky barrier type semiconductor device such as a Schottky barrier diode.

[0002]

2. Description of the Related Art In a Schottky barrier diode in which a metal electrode forming a Schottky junction is formed on the surface of a semiconductor, its electrical characteristics are almost determined by the Schottky junction. For a Schottky barrier diode that uses a semiconductor such as silicon, it is possible to control the height of the Schottky barrier by appropriately selecting the electrode material, and to create a diode with a low rising voltage. Can be done easily.

In recent years, since it is used for a high-speed switching power supply and the like, high-speed and low power consumption diodes are required, and compound semiconductors such as GaAs have been used for these diodes instead of silicon or the like. It was However, in GaAs and the like, there is not much room for selection of the electrode material, and it has been very difficult to control the rising voltage by selecting the electrode material. Therefore, a method of controlling the electrical characteristics of the Schottky barrier diode by using two kinds of metal materials having different Schottky barrier heights has been devised.
No. 81067 is disclosed.

FIGS. 6 (a) and 6 (b) are a plan view and a sectional view, respectively, showing a conventional Schottky barrier diode 51, in which a first barrier metal layer 52 is covered with an oxide film 55. The second barrier metal layer 53 having different Schottky barrier heights is vapor-deposited on the entire upper surface of the first barrier metal layer 52 by contacting the substrate 54 with the contact area with the substrate 54. The Schottky electrode 56 is formed so that the ratio of the contact area of the second barrier metal layer 53 with the substrate 54 becomes an appropriate value. At this time,
As shown in FIG. 7, the first barrier metal layer 52 may be formed of Mo, for example.
A metal material having a high Schottky barrier such as
By using a metal material having a low Schottky barrier, such as Ti, for the barrier metal layer 53 of, the forward characteristic and the reverse characteristic of the Schottky barrier diode 51 are respectively desired characteristics (however, pure Ti barrier metal and pure Ti barrier metal M
o between the properties in the case of barrier metals).

However, the disclosed method forms the Schottky electrode 56 by making the ratio of the contact areas of the two types of barrier metal layers 52 and 53 different, and an effective contact that can be actually implemented by this method. The area ratio is very limited. In addition, since the effective height of the Schottky barrier is merely controlled, the Schottky barrier diode 51 simultaneously satisfies all the basic characteristics such as a low forward rise voltage, a small reverse current, and a high breakdown voltage. I was not able to In other words, it is a trade-off that if the Schottky barrier is lowered to suppress the rising voltage, the reverse current becomes large, and if the Schottky barrier is raised to decrease the reverse current, the rising voltage becomes large. However, it was not possible to achieve a decrease in rising voltage and a decrease in reverse current at the same time.

[0006] Further, the applicants have developed and patented an ohmic Schottky coupled anode diode (OSBD) for the purpose of lowering the forward rising voltage. Although not shown, this OSBD
Has a Schottky electrode having a Schottky contact region around the ohmic contact region provided on the semiconductor substrate. Therefore, the forward rising voltage is ideally 0.
Although it can be made close to V, on the other hand, there is a problem that the reverse direction characteristic is deteriorated and the reverse direction leakage current increases, and in order to suppress it, a complicated structure must be adopted. , With technical difficulties.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the drawbacks of the above-mentioned conventional examples, and an object of the present invention is to reduce the forward rising voltage and the reverse current. It is to provide a Schottky barrier diode.

[0008]

According to another aspect of the present invention, there is provided a Schottky barrier semiconductor device in which a projection is formed on a surface of a semiconductor substrate, and at least a top surface of the projection has a low Schottky barrier height. A second Schottky metal region having a high Schottky barrier height is provided on both sides or around the first Schottky metal region, and a Schottky electrode is formed on the surface of the semiconductor substrate. There is.

At this time, it is preferable that inclined surfaces are formed on both sides or around the protrusion.

[0010]

In the Schottky barrier semiconductor device of the present invention, when the forward voltage is applied to the Schottky electrode, the depletion layer spread over the entire Schottky electrode disappears, and the Schottky electrode starts from the forward direction. Directional current flows.
At this time, since the depletion layer spreading from the first Schottky metal region having a low Schottky barrier disappears first due to the low forward voltage, a current path for the forward current flowing from the first Schottky metal region is secured, The forward voltage characteristic can be improved.

When a reverse voltage is applied, a depletion layer spreads under the Schottky electrode composed of the first Schottky metal region and the second Schottky metal region, and a current flowing to the Schottky electrode. The passage is blocked by the depletion layer and the reverse current is blocked. Particularly, when a high reverse voltage is applied, the voltage spreads from the second Schottky metal region having a high Schottky barrier until the withstand voltage of the first Schottky metal region having a low Schottky barrier is exceeded. Since the depletion layer blocks the current path formed on the first Schottky metal region side, the reverse current is blocked even at a high reverse voltage,
The reverse voltage characteristic can be improved. Further, during the low reverse voltage, the reverse current is blocked by the depletion layer spreading from the first Schottky metal region, and the reverse leakage current can be reduced.

As described above, the forward voltage characteristic is determined by the first Schottky metal region having a low Schottky barrier, and the reverse voltage characteristic is determined by the second Schottky metal region having a high Schottky barrier. Therefore, in the present invention, both the reverse voltage characteristic and the forward voltage characteristic can be improved at the same time, which can contribute to the improvement of the utilization efficiency of the switching power supply and the like.

At this time, if inclined surfaces are formed on both sides or the periphery of the protrusion, the current passage below the first Schottky metal region has, for example, a frustum shape, and the current passage cross-sectional area is the first Schottky metal. The area is larger than the area of the top surface, and the electric resistance of the current path is small.

[0014]

1 shows a Schottky barrier diode 1 according to an embodiment of the present invention. FIG. 1A is a plan view of the Schottky barrier diode 1, and FIG. 1B is a partially cutaway cross-sectional view of the Schottky barrier diode 1. The lower surface of a semiconductor substrate 2 such as a GaAs substrate is entirely ohmic-contacted by ohmic contact. An electrode 3 is provided. A large number of substantially trapezoidal protrusions 4 are provided on the upper surface of the semiconductor substrate 2 at regular intervals. A horizontal top surface 5 is formed on the upper surface of the protruding portion 4, and an inclined surface 6 is formed obliquely downward in the outer peripheral region of the protruding portion 4, and the protrusion surrounded by the horizontal top surface 5 and the inclined surface 6 is formed. Below the part 4, a flat lattice-shaped base part 7 is arranged.

A first Schottky metal film 8 having a low Schottky barrier is provided on the horizontal top surface 5 and is in Schottky contact with the top surface 5 of the protrusion 4. Further, a second Schottky metal film 9 having a high Schottky barrier is formed on the entire upper surface of the semiconductor substrate 2 from above the first Schottky metal film 8, and the second Schottky metal film 9 forms the inclined surface 6 and The base portion 7 is Schottky-bonded to the semiconductor substrate 2 in a lattice shape. As a result, the first Schottky metal film 8 and the second Schottky metal film 9 are electrically connected to each other, and the Schottky electrode 10 is formed on the entire upper surface of the semiconductor substrate 2. At this time, when a reverse voltage that causes avalanche breakdown is applied to the first Schottky metal film 8, the ohmic electrode 3 is formed by the second depletion layer 12 spreading from the second Schottky metal film 9. The size and position of the protrusion 4, the width of the base 7 and the like are designed so that the current path flowing from to the first Schottky metal film 8 is blocked.

For example, such a Schottky barrier diode 1 can be manufactured as follows.
First, 1 × 10 ¹⁴ to 2 × 1 is formed on an n ⁺ GaAs semiconductor substrate 2 which is highly doped with 1 × 10 ¹⁸ atoms / cm ³ or more.
The n-type active layer 13 of 0 ¹⁵ atoms / cm ³
It is formed to a thickness of 20 μm. The resist is patterned in a lattice pattern at a desired position by a lithography method, and the first Schottky metal film 8 made of a metal material having a low Schottky barrier, such as Au-Ge, is lifted off by a vacuum evaporation method. Then, the GaAs semiconductor substrate 2 is etched to a thickness of about 0.1 to 0.5 μm to form the inclined surface 6 and the base portion 7, and a metal material having a high Schottky barrier is formed on the entire upper surface of the GaAs semiconductor substrate 2 by oblique vacuum deposition. , A second Schottky metal film 9 of Pt-Ni or the like is formed by vapor deposition. At this time, the inclined surface 6 also has a second
The Schottky metal film 9 is formed. After that, heat treatment is performed at 300 to 400 ° C. to alloy them to form the Schottky electrode 10. Finally, the Au—Ge / Ni-based ohmic electrode 3 is formed on the back surface of the semiconductor substrate 2 to manufacture the Schottky barrier diode 1.

Thus, in the Schottky barrier diode 1 thus manufactured, the forward voltage Vf1 or higher between the Schottky electrode 10 and the ohmic electrode 3 is equal to or higher than the forward rising voltage Vf1 of the first Schottky metal film 8. When the directional voltage Vs (that is, Vf1 <Vs) is applied, the first depletion layer 11 spreading from the first Schottky metal film 8 toward the protrusion 4 disappears as shown in FIG. 2A. Since the second depletion layer 12 extending from the second Schottky metal film 9 is small, the current path from the first Schottky metal film 8 to the ohmic electrode 3 is opened, and the Schottky electrode 10 is opened. A forward current flows between the ohmic electrode 3 and the ohmic electrode 3. Moreover, since the Schottky barrier of the first Schottky metal film 8 of the protrusion 4 is low, a forward current can flow even with a small forward current voltage, and good forward voltage characteristics can be obtained.

On the other hand, when a reverse voltage is applied between the Schottky electrode 10 and the ohmic electrode 3,
As shown in FIG. 2B, when the reverse voltage is low, more specifically, during the reverse voltage Vs smaller than the breakdown voltage BV1 of the first Schottky metal film 8 (that is, BV1 <Vs <
Vf1) is from the first Schottky metal film 8 to the protrusion 4
The current path in the protrusion 4 is blocked by the first depletion layer 11 that spreads toward, and almost no leak current flows in the reverse direction. Further, when the reverse voltage is further increased, the second depletion layer 11 spreads from the second Schottky metal film 9 to the lower side of the protrusion 4 as shown in FIG. In the vicinity of the withstand voltage of the key metal film 8, the second
The depletion layer 12 surely blocks the current path in the protrusion 4. As a result, even if a reverse voltage exceeding the breakdown voltage of the first Schottky metal film 8 is applied (BV2 <Vs <B
V1), no reverse current flows between the Schottky electrode 10 and the ohmic electrode 3. Moreover, the reverse current is the second
Since the current does not flow until the withstand voltage BV2 of the Schottky metal film 9 is exceeded, a large reverse voltage can be applied and good reverse voltage characteristics can be obtained.

Further, since the protrusion 4 serving as a current path has an inverted trapezoidal shape, the narrow upper portion is surely blocked by the second depletion layer 12, while the protrusion 4 is wide at the lower portion. Therefore, the internal resistance between the Schottky electrode 10 and the ohmic electrode 3 is small.

FIG. 3 shows an example of electrical characteristics of the Schottky barrier diode 1 according to the present invention. The forward current-voltage characteristic of the Schottky barrier diode 1 is shown in FIG.
As shown by the solid line (a), the forward rising voltage could be lowered to about 0.2 V. This is equal to the rising voltage when the Schottky electrode is formed only by the first Schottky metal film having a low Schottky barrier (broken line B), and shot only by the second Schottky metal film having a high Schottky barrier. It was lower than the rising voltage (about 0.7 V) when the key electrode was manufactured (broken line C). The reverse current-voltage characteristic is shown in FIG. 3B. As shown by the solid line D, the breakdown voltage of the Schottky barrier diode 1 can be increased up to about 180 V, which is the first Schottky metal. It is much higher than the breakdown voltage when the Schottky electrode is formed only by the film (broken line E), and is the same as the breakdown voltage when the Schottky electrode is formed only by the second Schottky metal film (broken line F). . Also, the leakage current in the reverse direction is smaller than that in the case where the Schottky electrode is formed only by the first Schottky metal film (broken line E), and the second shot is generated when the voltage is equal to or higher than a certain voltage (about 90 V). The value is reduced to the same level as when the Schottky electrode is made of only the key metal film (dashed line F).

As described above, in the Schottky barrier diode 1 according to the present invention, the forward voltage can be lowered while maintaining the reverse withstand voltage and the leak current at the conventional characteristics, and particularly, about 10 MHz to 20 MHz. Is preferable as a diode for a high speed switching power supply that operates at high speed, and such a Schottky barrier diode 1
By using, it is possible to contribute to the improvement of the conversion efficiency of the switching power supply.

FIG. 4 is an operation explanatory view of a Schottky barrier diode 21 which is another embodiment of the present invention. The Schottky barrier diode 21 extends from the base portion 7 of the semiconductor substrate 2 to the inclined surface 6. , A second Schottky metal film 9 having a high Schottky barrier is provided in a grid pattern. In addition, the second Schottky metal film 9
A first Schottky metal film 8 having a low Schottky barrier is formed over the entire upper surface of the semiconductor substrate 2 and the upper surface of the semiconductor substrate 2, and the first Schottky metal film 8 includes the inclined surface 6 and the top surface 5.
Is Schottky bonded to the protrusion 4. As a result,
The first Schottky metal film 8 and the second Schottky metal film 9 are electrically connected to each other, and the Schottky electrode 10 is formed on the entire upper surface of the semiconductor substrate 2. Of course, also in this embodiment, when a reverse voltage that causes avalanche breakdown is applied to the first Schottky metal film 8, the second Schottky metal film 9 spreads from the second Schottky metal film 9.
The size and position of the protrusion 4 and the region of the second Schottky metal film 9 are designed so that the current path flowing from the ohmic electrode 3 to the first Schottky metal film 8 is blocked by the depletion layer 12 of FIG. Has been done.

This Schottky barrier diode 21
Can be produced, for example, as follows. First, 1 × 10 ¹⁴ to 2 × 10 ¹⁵ a is formed on an n ⁺ GaAs semiconductor substrate 2 which is highly doped with 1 × 10 ¹⁸ atoms / cm ³ or more.
An n-type doped active layer of toms / cm ³ is formed to a thickness of 10 to 20 μm. After patterning the resist in a grid pattern at a desired position by a lithography method, Pt- having a high Schottky barrier is formed by a vacuum deposition method or a sputtering method.
The second Schottky metal film 9 made of Ni or the like is formed on the base portion 7.
And formed on the inclined surface 6 and alloyed at about 400 ° C. Next, A having a low Schottky barrier is formed on the entire upper surface of the semiconductor substrate 2.
u-Ge is vapor-deposited to form the first Schottky metal film 8, and heat treatment is performed at about 300 ° C. for about 1 hour to form the Schottky electrode 10. Further, an upper surface electrode (not shown) made of Ti / Ni / Au is formed on the entire surface of the Schottky electrode 10 so that wire bonding and soldering can be easily performed. Finally, the Au—Ge / Ni-based ohmic electrode 3 is formed on the back surface of the semiconductor substrate 2 to manufacture the Schottky barrier diode 21.

Therefore, when a forward voltage Vs (that is, Vf1 <Vs) which is equal to or higher than the forward rising voltage Vf1 of the first Schottky metal film 8 is applied between the Schottky electrode 10 and the ohmic electrode 3, As shown in FIG. 4A, the first depletion layer 11 spreading from the first Schottky metal film 8 toward the protrusion 4 disappears and the second depletion layer 11 spreading from the second Schottky metal film 9 disappears. The depletion layer 12 of the Schottky electrode 1 becomes smaller, the current path from the first Schottky metal film 8 is opened, and the Schottky electrode 1 is formed by the low forward voltage.
A forward current flows between 0 and the ohmic electrode 3. On the other hand, a reverse voltage Vs smaller than the withstand voltage BV1 of the first Schottky electrode film 8 is applied between the Schottky electrode 10 and the ohmic electrode 3 (BV1 <Vs <V
In the case of f1), as shown in FIG. 4B, the first depletion layer 11 spreading from the first Schottky metal film 8 toward the protrusion 4 blocks the current passage in the protrusion 4. ,
Almost no leak current flows in the reverse direction. Further, as the reverse voltage is further increased, the second depletion layer 12 spreads downward from the second Schottky metal film 9 toward the lower portion of the protrusion 4 as shown in FIG. Even if the breakdown voltage BV1 of the Schottky metal film 8 is exceeded (BV2 <Vs <BV1),
The second depletion layer 12 extending from the second Schottky metal film 9 surely blocks the current path in the protrusion 4. As a result, no reverse current flows between the Schottky electrode 10 and the ohmic electrode 3. Moreover, as in the first embodiment, since the Schottky barrier of the second Schottky metal film 9 is high, the reverse current does not flow even if a high reverse voltage is applied, and the Schottky barrier diode 21. The reverse breakdown voltage can be increased.

At this time, since the second Schottky metal film 9 is provided so as to cover the inclined surface 6 below the protrusion 4, the second depletion layer is easily formed on the upper portion of the protrusion 4 where the width is narrow. The current path is reliably cut off by this. On the other hand, since the width of the protrusion 4 is wide at the lower portion, the internal resistance between the Schottky electrode 10 and the ohmic electrode 3 is small.

FIG. 5 is a plan view showing a Schottky barrier diode 31 which is still another embodiment of the present invention.
The first Schottky metal film 8 having a low Schottky barrier does not necessarily have to be provided in an island shape, and may have an elongated shape such as a strip shape as shown in FIG.

[0027]

According to the present invention, a forward current can be obtained with a low forward voltage, and a reverse current can be blocked with a high reverse voltage. The voltage characteristics can be improved at the same time. Further, when the reverse voltage is applied, the leak current in the reverse direction can be reduced.

At this time, if inclined surfaces are formed on both sides or the periphery of the protrusion, the current passage below the first Schottky metal region has, for example, a frustum shape, and the electric resistance of the current passage can be reduced. .

[Brief description of drawings]

1A and 1B are a plan view and a cross-sectional view, respectively, showing a Schottky barrier semiconductor device which is an embodiment of the present invention.

2A, 2B, and 2C are operation explanatory diagrams in the Schottky barrier semiconductor device of the above.

FIG. 3A is a diagram showing a forward current-voltage characteristic in the Schottky barrier semiconductor device of the above, and FIG. 3B is a diagram showing a reverse current-voltage characteristic of the Schottky barrier semiconductor device in the same.

4A, 4B, and 4C are operation explanatory views of a Schottky barrier semiconductor device according to another embodiment of the present invention.

FIG. 5 is a plan view showing a Schottky barrier semiconductor device which is still another embodiment of the present invention.

6A and 6B are a plan view and a cross-sectional view showing a conventional Schottky barrier diode, respectively.

FIG. 7 is a partially cutaway sectional view showing the Schottky barrier diode of the above.

[Explanation of symbols]

 2 Semiconductor Substrate 4 Projection 6 Slope 7 Base 8 First Schottky Barrier Metal Film 9 Second Schottky Barrier Metal Film 11 First Depletion Layer 12 Second Depletion Layer

Claims (2)

[Claims] 1. A protrusion is formed on a surface of a semiconductor substrate, a first Schottky metal region having a low Schottky barrier is provided on at least a top surface of the protrusion, and both sides of the first Schottky metal region or A Schottky barrier semiconductor device, wherein a second Schottky metal region having a high Schottky barrier is provided in the periphery to form a Schottky electrode on the surface of the semiconductor substrate. 2. The Schottky barrier semiconductor device according to claim 1, wherein inclined surfaces are formed on both sides or the periphery of the protrusion.