JPH10303436A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reverse recovery resistance of a planar diode having a high withstand voltage and a large current. SOLUTION: On the surface of an n<-> -type substrate 1, a p<-> -type well region 6 and a p<+> -type region for guard ring forming a voltage-resistant structure 10 are formed as an anode region 11 by performing diffusion called 'drive' after implanting impurity ions and an anode electrode 3 is formed of a metallic film composed of an aluminum film, etc., on the well region 6. On the surface of the substrate 1 on the opposite side of the anode region 11, a cathode region 2 composed of a high-concentration n-type region is formed and a cathode electrode 4 is formed of a metallic film composed of an aluminum film, etc., on the region 2. The impurity concentration in the anode region 11 is reduced by two or more digits as compared with the conventional example.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor device such as a power diode used for power conversion equipment.

[0002]

2. Description of the Related Art A high-speed diode used as a freewheeling diode or a snubber diode in combination with a power switching element such as an IGBT which can be used for power conversion equipment, can perform high-speed switching, and can obtain a low saturation voltage, has a low order. Voltage drop and high speed are required. As the high-speed diode, a Schottky diode or a planar pn diode is usually used according to the voltage / current capacity of the power switching element.

FIG. 5 is a cross-sectional view of a main part of a conventional planar pn diode. p ^{+ is applied to} one main surface of n ⁻ substrate 1
The anode region 11 formed by the well region 5 and the p ⁺ region of the guard ring 21 as the breakdown voltage structure 10 are formed by impurity ion implantation and subsequent diffusion called drive. On the anode region 11, the anode electrode 3 is formed of a metal film such as an aluminum film. A cathode region 2 which is an n-type high-concentration region is formed on the surface of the n ⁻ substrate 1 opposite to the anode region 11 side, and a cathode electrode 4 is formed on the cathode region 2 with a metal film such as an aluminum film. ing.

The operation of this diode will be described below.
When a negative potential is applied to the anode electrode 3 and a positive potential is applied to the cathode electrode 4, a reverse blocking state occurs and no current flows. However, when a positive potential is applied to the anode electrode 3 and a negative potential is applied to the cathode electrode 4, the diode becomes forward. Direction, a hole is injected from the anode region 11 into the n ⁻ substrate 1, and electrons from the cathode region 2 pass through the n ⁻ substrate 1 to the anode region 1.
Injected into 1. As a result, n ⁻ substrate 1 is filled with excess holes and excess electrons, and a current flows through the diode. The injected holes and electrons become minority carriers on the injected side.

FIG. 6 is a sectional view showing a main part of another conventional planar pn diode. A p ^- well region 5 is provided at the center of the anode region 11, and a planar ring-shaped p ⁺ well region 6 is provided at a peripheral terminal portion 30 for ensuring a withstand voltage. By deeply diffusing the p ⁺ well region 11, the curvature at the peripheral terminal portion 30 of the anode region 11 is increased, the electric field concentration is reduced, and the breakdown voltage is improved.

When a reverse current is suddenly supplied from a state in which a forward current is applied to the diode to reversely recover the diode, minority carriers injected during forward energization are swept out and reduced. In addition, the depletion layer expands due to the reverse voltage and enters a reverse blocking state. A reverse recovery loss occurs due to the product of the reverse recovery current and the reverse voltage flowing during the reverse recovery operation. If the loss is excessive, the diode is destroyed. An element that does not cause this destruction, that is, an element that has a high reverse recovery resistance is desired. In particular, speeding up of switching elements such as IGBTs,
As the capacity increases, a reverse recovery characteristic that can perform a high-speed switching operation and is not destroyed even by a large current is required for a diode used in combination.

In the case of a planar pn diode, the destruction of the element due to the reverse recovery is caused by the termination 3 around the anode region 11.
Many occurrences occur at 0. This is where the electric field strength becomes highest when a reverse voltage is applied, and where the reverse current during reverse recovery is concentrated most. for that reason,
The stress at the time of reverse recovery is applied to the peripheral end portion 30 from the central portion of the element.

[0008]

As the breakdown voltage and current of the planar type pn diode increase, a large amount of device destruction during reverse recovery occurs at the peripheral edge of the anode region on the surface of the device, and the reverse recovery withstand capability is reduced. This causes a problem of deterioration. An object of the present invention is to solve the above-mentioned problem and to provide a semiconductor device having a strong reverse recovery withstand capability.

[0009]

In order to achieve the above object, a second semiconductor region of a second conductivity type is selectively formed on one main surface of a first semiconductor region of a low concentration of a first conductivity type. And
A high-concentration third semiconductor region of the first conductivity type is formed on the other main surface of the first semiconductor region, and is formed on the second semiconductor region and the third semiconductor region.
In a semiconductor device in which an anode electrode and a cathode electrode are formed on a semiconductor region, an outer peripheral region of the second semiconductor region has a lower impurity concentration than an inner region surrounded by the outer peripheral region.

It is preferable that the internal region of the second semiconductor region is formed of a low concentration region. The internal region of the second semiconductor region may be formed of a low-concentration region and a high-concentration region.
Preferably, a plurality of high-concentration regions are formed in the low-concentration region inside the second semiconductor region.

It is effective that the low-concentration region of the second semiconductor region has a surface concentration of 5 × 10 ¹⁵ cm ^-3 to 1 × 10 ¹⁷ cm ^-3 . It is preferable that the diffusion depth of the outer peripheral region of the second semiconductor region is 0.5 μm to 2 μm.
As described above, by lowering the impurity concentration at the peripheral end portion of the anode region where the breakdown is concentrated, injection of holes from the periphery of the anode region during forward conduction is suppressed, and stress during reverse recovery is reduced. Is concentrated, and the injection of holes, which are minority carriers, into the n ⁻ substrate immediately below is suppressed. Further, the minority carriers (holes) extracted during the reverse recovery do not concentrate on the peripheral end portion of the anode region where the electric field is strongest, but are dispersed in the central portion of the element where the concentration of the anode region is high. As a result, it is possible to prevent heat generation due to the concentration of the reverse recovery current, which causes the device breakdown at the time of the reverse recovery, and the device breakdown accompanying the heat.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A and 1B are main part structural diagrams of a first embodiment of the present invention. FIG. 1A is a plan view, and FIG. 1B is a sectional view taken along line XX of FIG. It is sectional drawing which cut | disconnected. In FIG. 2B, a detailed description of the breakdown voltage structure 10 is omitted.
In FIG. 1, a p ⁻ well region 6 as an anode region 11 on the surface of an n ⁻ substrate 1 and a guard ring p ⁺ region (not shown) forming a breakdown voltage structure 10 serve as a drive after impurity ion implantation. It is formed by diffusion. On p ^- well region 6, anode electrode 3 is formed of a metal film such as an aluminum film. On the surface of the n ⁻ substrate 1 on the side opposite to the anode region 11 side, a cathode region 2 that is a high-concentration n-type region is formed.
The cathode electrode 4 is formed thereon with a metal film such as an aluminum film. The structure is the same as the structure of FIG. 5 described in the section of the prior art, except that the anode region 11 is formed by the p ^- well region 6 whose impurity concentration is lower by two digits or more. Thus, the same effect as when the impurity concentration of the peripheral termination portion 30 of the anode region 11 is lowered, that is, the reverse recovery withstand capability can be improved.

In this structure, the process of manufacturing the element is simple,
Moreover, it is good that it is easy. Further, by adjusting the conditions of ion implantation and the conditions of diffusion as a subsequent drive, a device having high reverse recovery withstand capability can be easily obtained. But,
Since the injection of minority carriers that play an important role in the forward characteristics is suppressed, the forward voltage drop in the large current region increases.

FIGS. 2A and 2B are diagrams showing the main parts of a second embodiment of the present invention. FIG. 2A is a plan view, and FIG.
It is sectional drawing cut | disconnected by -X-ray. In FIG. 2B, a detailed description of the breakdown voltage structure 10 is omitted. In FIG. 2, p ⁺ as an anode region 11 is formed on the surface of an n ⁻ substrate 1.
Well region 5 and p ^- well region 6 are formed so as to surround it. A guard ring p ⁺ region (not shown), which is a breakdown voltage structure 10, is formed therearound. These regions are formed through ion implantation and diffusion as described above. A cathode electrode 4 is provided on the surface of the n ⁻ substrate 1 opposite to the anode region 11 via a cathode region 2.

Although the anode region 11 of the element is composed of the p ⁺ well region 5 and the p ⁻ well region 6, it is a matter of course that a plurality of p well regions having an intermediate surface concentration between these regions may be formed. Here, only two types are shown. In this embodiment, a p ⁺ well region 5 of a high concentration region is provided at a central portion of the device.
And ap ⁻ well region 6 of a low concentration region is arranged so as to surround this. Minority carriers injected into the n ^- substrate 1 under the breakdown voltage structure 10 do not concentrate at the junction of the peripheral termination portion 30 of the anode region 11 at the time of the reverse recovery, and the peripheral p ^- well region 6 and the central p ⁺ well region 5
And contributes to the improvement of reverse recovery withstand.

In this structure, the reverse recovery characteristic is almost absent.
Determined at the center of the node area 11, p ⁺Well region 5 and p
^-By adjusting the area ratio with the well region 6, the switch
Improve switching loss and soft recovery characteristics
Can be. Also, the p of the high concentration region is⁺Well territory
By arranging region 5, it is possible to increase the injection of minority carriers.
Can be. This increases the forward voltage drop in the large current region.
Large size can be suppressed, preventing element breakdown due to surge current
can do.

FIGS. 3 (a) and 3 (b) show a main part of a third embodiment of the present invention. FIG. 3 (a) is a plan view and FIG.
It is sectional drawing cut | disconnected by -X-ray. In FIG. 1B, a detailed description of the breakdown voltage structure 10 is omitted. In FIG. 3, a p ⁺ well region 5 as an anode region 11 is formed on a surface layer of an n ⁻ substrate 1 in a stripe cell shape (rectangular cell shape).
And ap ^- well region 6 is formed so as to surround it. A guard ring p ⁺ region (not shown), which is a breakdown voltage structure 10, is formed therearound. These are formed through diffusion after impurity ion implantation. An anode electrode 3 is formed on p ⁺ well region 5 and p ⁻ well region 6. A cathode electrode 4 is provided on a surface of the n ⁻ substrate 1 opposite to the anode region 11 side with a cathode region 2 interposed therebetween.

Thus, p⁺Providing a plurality of well regions 5
And p^-To be surrounded by the well region 6
As in the second embodiment,
n^-The minority carriers injected into the substrate 1
Concentrate on the junction of the peripheral end portion 30 of the node region 11
Without the surrounding p^-Well region 6 and a plurality of ps in the center
⁺The flow is dispersed in the well region 5 and contributes to the improvement of the reverse recovery resistance.
Give. Also, this structure is p⁺Well region 5 and p^-Ue
The reverse recovery characteristic and the
The trade-off of the forward characteristic can be optimized.
Furthermore, in terms of pressure resistance, p⁺N from the tip of well region 5^-
The extension of the depletion layer to the substrate 1 is suppressed, and n ^-Sky in substrate 1
The region where the poor layer does not spread is wider than in the second embodiment, and p^-
Leakage current, including when the well region 6 punches through
The increase in the flow can be suppressed, and the withstand voltage characteristics are more improved than in the second embodiment.
Can be up.

FIGS. 4A and 4B are diagrams showing the main parts of a fourth embodiment of the present invention. FIG. 4A is a plan view, and FIG.
It is sectional drawing cut | disconnected by -X-ray. In FIG. 2B, a detailed description of the breakdown voltage structure 10 is omitted. 4, p ⁺ well regions 5 arranged in a stoichiometric cell shape in FIG. 3 are arranged in a circular island shape. Also, they may be arranged in a polygonal island shape. Also in these cases, the p ⁺ well region 5 in the high concentration region is arranged so as to be surrounded by the p ⁻ well region 6 in the low concentration region.

In the above embodiment, in order to improve the reverse recovery characteristic, the surface concentration of the p ^- well region 6 in the low concentration region is set to 5 × 10 ¹⁵ cm ⁻³ or more and 1 × 10 ¹⁷ cm ⁻³ or less. Adjustment is suitable for obtaining good device characteristics.
If it is less than 5 × 10 ¹⁵ cm ⁻³ , the elongation of the depletion layer increases,
Leakage current increases. On the other hand, if it exceeds 1 × 10 ¹⁷ cm ⁻³ , the effect of the low concentration is diminished. Also preferably 1 × 10 ¹⁶ c
It is preferable that the adjustment be made in the range of m ⁻³ or more and 2 × 10 ¹⁶ cm ⁻³ or less.

In consideration of the surge current characteristics, the p ⁺ well region 5, which is a high concentration region, needs to be 1 × 10 ¹⁸ cm ⁻³ or more. deterioration of reverse recovery characteristics due to high concentration of the p ⁺ well region 5 can be prevented by adjusting the area ratio of the p ⁺ well region 5. In addition, it is desirable that the diffusion depth of the p ^- well region 6 which is a low concentration region is made as small as possible in consideration of implantation. However, the resistance to a large current requires a certain diffusion depth in view of the influence of defects on the silicon surface and mechanical strength. Also, there is a concern that leakage current may increase due to punch-through.
^- diffusion depth of the well region 6 is preferably 2μm or less 0.5μm or more. When the diffusion depth of p ^- well region 6 is 2 μm or more, the injection amount of minority carriers from p ^- well region 6 to n ⁻ substrate 1 increases, and the electric field strength in peripheral termination portion 30 increases, which is opposite to the above. The recovery tolerance decreases. 0.
If the thickness is less than 5 μm, the injection efficiency becomes extremely poor and the depletion layer is not applicable because of punch-through. Further, the thickness is preferably 1 μm or more and 2 μm or less.

[0022]

According to the present invention, the reverse endurance can be improved by lowering the concentration of the peripheral end of the anode region. The anode region is composed of a p ⁺ well region and a p ^- well region, and by adjusting the area ratio, the reverse recovery characteristics (reverse recovery current, soft recovery, etc.)
And the trade-off between forward characteristics (forward voltage drop) can be optimized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main part of a first embodiment of the present invention, and FIG.
Is a plan view, and (b) is a cross-sectional view taken along line XX of (a).

FIGS. 2A and 2B are main part configuration diagrams of a second embodiment of the present invention, wherein FIG.
Is a plan view, and (b) is a cross-sectional view taken along line XX of (a).

FIGS. 3A and 3B are main part configuration diagrams of a third embodiment of the present invention, wherein FIG.
Is a plan view, and (b) is a cross-sectional view taken along line XX of (a).

FIGS. 4A and 4B are configuration diagrams of a main part of a fourth embodiment of the present invention, wherein FIG.
Is a plan view, and (b) is a cross-sectional view taken along line XX of (a).

FIG. 5 is a sectional view of a main part of a conventional pn diode.

FIG. 6 is a sectional structural view of a main part of another conventional pn diode.

[Explanation of symbols]

Reference Signs List 1 n ^- substrate 2 cathode region 3 anode electrode 4 cathode electrode 5 p ⁺ well region 6 p ^- well region 10 breakdown voltage structure 11 anode region 21 guard ring 30 peripheral terminal portion

Claims (6)

[Claims] A second semiconductor region of a second conductivity type is selectively formed on one main surface of the low-concentration first semiconductor region of the first conductivity type, and a second semiconductor region of the second conductivity type is formed on the other main surface of the first semiconductor region; In a semiconductor device in which a third semiconductor region of a first conductivity type having a high concentration is formed, and an anode electrode and a cathode electrode are respectively formed on the second semiconductor region and the third semiconductor region, an outer peripheral region of the second semiconductor region Has a lower impurity concentration than an inner region surrounded by the outer peripheral region. 2. The semiconductor device according to claim 1, wherein the internal region of the second semiconductor region is formed of a low concentration region. 3. The semiconductor device according to claim 1, wherein the internal region of the second semiconductor region is formed of a low concentration region and a high concentration region. 4. The semiconductor device according to claim 3, wherein a plurality of high-concentration regions are formed in the low-concentration region inside the second semiconductor region. 5. The method according to claim 1, wherein the surface concentration of the low concentration region of the second semiconductor region is 5 × 10 ¹⁵ cm ⁻³ to 1 × 10 ¹⁷ cm ⁻³ . Semiconductor device. 6. The semiconductor device according to claim 1, wherein the diffusion depth of the outer peripheral region of the second semiconductor region is 0.5 μm to 2 μm.