JPH03276679A - Schottky barrier diode - Google Patents

Abstract

PURPOSE:To improve more a breakdown strength in a simple structure by a method wherein a semiconductor layer has an impurity concentration part, whose impurity concentration under the peripheral parts of a Schottky electrode is set lower than that under the central part of the electrode. CONSTITUTION:An n<-> layer 2b of an impurity concentration smaller than that of an n<-> type layer 2a is formed under the peripheral parts of a Schottky electrode 3. A depletion layer 5a is formed larger its width in the layer 2b than its width in the layer 2a because the impurity concentration of the layer 2b is smaller than that of the layer 2a. Thereby, the width of the layer 5a is unified so as to become small for field-effect concentration due to a surface charge in the surface part of the layer 5a, but the width, which is positioned in the vicinity of the surface of the layer 2b, of the layer 5a is still larger than that in the interior of the layer 5a. Accordingly, it is eliminated that a breakdown is caused in the surface of the layer 5a earlier than that in the interior of the layer 5a and a breakdown strength VB can be improved to a value which is determined by an intrinsic junction condition.

Description

[Detailed description of the invention] [Industrial application field] INDUSTRIAL APPLICATION This invention is utilized for a Schottky barrier diode.

The present invention is particularly applicable to high voltage Schottky barrier diodes.

〔overview〕

The present invention provides a Schottky diode including a semiconductor layer and a Schottky electrode provided on the semiconductor layer, in which the impurity concentration in the semiconductor layer is lower in the peripheral portion of the Schottky electrode than in the center thereof. This improves the withstand voltage.

[Conventional technology]

FIG. 4 is a schematic cross-sectional view showing an example of a conventional Schottky barrier diode, showing a planar structure.

For example, a layer 2 is formed on the main surface of an n'' substrate 1 made of silicon, a Schottky electrode 3 made of molybdenum, for example, is formed at a predetermined position on this n layer 2, and a Schottky electrode 3 made of, for example, molybdenum is formed on the n'' substrate 1. An ohmic electrode 4 made of aluminum, for example, is formed on the bottom surface.

And between the Schottky electrode 3 and the ohmic electrode 4,
By applying a positive voltage with the Schottky electrode 3 on the (+) side, a positive current consisting of a Schottky current flows, and when applying a negative voltage VR with the Schottky electrode 3 on the (-) side, no current flows. Only leakage current will flow.

FIG. 5 shows the state of the Schottky junction when this negative voltage V is applied. A depletion layer 5 corresponding to the magnitude of the applied negative voltage VIl is formed, and this depletion layer 5 maintains a breakdown voltage.

Generally, the withstand voltage (breakdown voltage) VB of such a diode is such that at the surface of the junction, the width of the depletion layer 5 is smaller than that inside the junction due to electric field concentration based on the surface charge, resulting in breakdown (mainly avalanche breakdown). ).

It is known that this is due to so-called surface breakdown.

Various efforts have been made to improve the withstand voltage of such diodes and to prevent the above-mentioned surface breakdown.

FIG. 6 shows a guard ring structure as an example. In this guard ring structure, the p-well 6 is formed close to the end of the Schottky electrode 3. As the magnitude of the applied negative voltage increases, the depletion layer reaches the p-well 6, causing punch-through, and the p-well 6
The depletion layer grows from there, and as a result, the withstand voltage is improved.

Furthermore, there is a field plate structure in which an oxide film is formed in contact with the end of the Schottky electrode, and the Schottky electrode extends onto the oxide film.

This is intended to neutralize the influence of surface charges and improve breakdown voltage.

References, Baba: "Technical Trends in Increasing the Withstand Voltage of rP-n Junctions" Sanken Giho, Vol. 14, No. 11982 [Problems to be Solved by the Invention] The measures to improve the withstand voltage of the diodes mentioned above include the following. There is a problem.

(1) Although the planar structure is the simplest and most desirable structure to manufacture, electric field concentration at the ends of the Schottky electrode cannot be prevented.

[2) In the guard ring structure, electric field concentration in the p-well portion still poses a problem.

(3) In the field plate structure, surface leakage current occurs at the interface between the oxide film and the substrate, and the capacitance becomes large, which causes problems in high-frequency operation.

Furthermore, the guard ring structure and field structure have the problem of complicating the manufacturing process.

The purpose of the present invention is to solve the above-mentioned problems.
An object of the present invention is to provide a Schottky barrier diode that has a simple structure and can further improve breakdown voltage.

[Means to solve the problem]

The present invention provides a Schottky barrier diode comprising a semiconductor layer of one conductivity type and a Schottky electrode provided on the semiconductor layer, wherein the semiconductor layer has an impurity concentration in a peripheral portion of the Schottky electrode. It is characterized by having an impurity concentration distribution set lower than the impurity concentration in the central portion.

Further, in the present invention, it is preferable that a high impurity concentration region of an opposite conductivity type is provided at an end portion of the Schottky electrode on the semiconductor layer that is not under the Schottky barrier electrode.

[Effect]

Since the impurity concentration of the semiconductor layer is set to be lower in the peripheral part of the Schottky electrode than in the central part, the width of the depletion layer in the peripheral part of the Schottky electrode is larger than in the central part.

Therefore, even if electric field concentration occurs at the junction surface due to surface charge and the width of the depletion layer becomes smaller, the width of the depletion layer can be kept larger than the width of the internal depletion layer, preventing surface breakdown and improving breakdown voltage. It becomes possible to do so.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view showing a first embodiment of the present invention.

In this embodiment, for example, the impurity concentration I
1019 cm-''n' substrate 1, four layers 2as formed on the main surface of this n' substrate 1 with impurity concentration IXIQ15 cm-3, and impurity concentration 1.5 xlO'' cm-3.
n-layer 2b and 1 so that the end portion is over the n-layer 2b.
It includes a Schottky electrode 3 made of, for example, tungsten, formed on the layer 2a, and an ohmic electrode 4, made of, for example, aluminum, formed on the bottom surface of the n' substrate 1.

The feature of the present invention is that in FIG. 1, the impurity concentration is 1 layer 2
This is because the n- layer 2b, which is smaller than a, is formed around the Schottky electrode 3.

Next, the operation of this embodiment at the time of reverse bias will be explained.

FIG. 2 is an explanatory diagram showing the state of bonding when a negative voltage V is applied to the Schottky electrode 3 in the first embodiment shown in FIG. In this practical example, the depletion layer 5a is
Since the impurity concentration of n- layer 2b is lower than that of layer 1 2a, n
The width of layer 2b is larger than that of layer 1 2a.Thus, although the width of the t1 depletion layer 5a is rounded to be smaller due to electric field concentration due to surface charges at the surface portion, The width of the depletion layer 5a is larger than the width inside.Therefore, breakdown does not occur at the surface before the inside, and the breakdown voltage vB can be improved to a value determined by the original junction conditions.

Next, the manufacturing method of this example will be briefly explained.

First, an n-type silicon substrate with an impurity concentration I
An n-type silicon layer of several μm thick (7) of
One layer 2a of 10l5 is formed. Next, the end is n-layer 2
A Schottky electrode 3 is formed by vapor depositing molybdenum, for example, on the n layer 2a so as to slightly cover the n layer 2a, a lead wire is taken out, and finally, an ohmic electrode 4 is formed by vapor depositing aluminum, for example, on the bottom surface of the n layer 2a. form and take out the lead wire.

As explained above, the Schottky barrier diode of this embodiment can be easily manufactured by simply adding the step of forming one layer 2a by the usual selective diffusion method.

FIG. 3 is a schematic sectional view showing a second embodiment of the present invention.

The second embodiment is a modification of the first embodiment shown in FIG. 1 to the conventional guard ring structure shown in FIG. 6. That is, a p-well 6 with a high impurity concentration is formed near the end of the Schottky electrode 3 on the n-layer 2b. In this case, the p-well 6 is formed at a distance from the end of the Schottky electrode 3 because the depletion layer has a larger spread than in the conventional example shown in FIG.

In the second embodiment, since the distance between the p-well 6 and the end of the Schottky electrode 3 can be increased, the punch-through voltage can be increased and the effect of the guard ring can be enhanced. Combined with the effects shown in , it is possible to further improve the breakdown voltage.

In the embodiments described above, the impurity concentration distribution of the semiconductor layer is divided into two regions, the 1 layer 2a and the n-layer 2b, but the division of these regions is not necessarily step-like. It is not necessary, and the impurity concentration may be sloped such that the impurity concentration gradually decreases from the center toward the periphery of the Schottky electrode.

〔Effect of the invention〕

As explained above, the present invention makes the impurity concentration in the semiconductor layer in which the Schottky electrode is formed lower in the peripheral part of the Schottky electrode than in the central part.
The width of the depletion layer at the periphery of the Schottky electrode can be made larger than that inside the Schottky electrode, and the simple structure has the effect of alleviating electric field concentration due to surface charges and improving reverse breakdown voltage characteristics without deteriorating forward characteristics. .

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing a first embodiment of the present invention. FIG. 2 is an explanatory diagram showing the state of the junction at the time of reverse bias. FIG. 3 is a schematic sectional view showing a second embodiment of the present invention. FIG. 4 is a schematic cross-sectional view showing a conventional example. FIG. 5 is an explanatory diagram showing the state of the junction at the time of reverse bias. FIG. 6 is a schematic sectional view showing another conventional example. 1-n+ substrate, 2.2a-n layer, 2b-n- layer, 3...
・Schottky electrode, 4... Ohmic electrode, 5.5
a...depletion layer, 6...p well.

Claims (1)

[Claims] 1. In a Schottky barrier diode comprising a semiconductor layer of one conductivity type and a Schottky electrode provided on the semiconductor layer, the semiconductor layer is arranged in a peripheral portion of the Schottky electrode. A Schottky barrier diode characterized in that it has an impurity concentration distribution in which the impurity concentration is set lower than the impurity concentration in its central portion. 2. The Schottky barrier diode according to claim 1, wherein a high impurity concentration region of an opposite conductivity type is provided at an end portion of the Schottky electrode on the semiconductor layer that is not under the Schottky barrier electrode.