JP2002076370A - Super junction schottky diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To speed up the switching of a Schottky barrier diode having a super junction structure which flows a current in on-state and depletes in off-state. SOLUTION: A high resistance region 11 having a substantially high resistivity is inserted between a p-column 10 forming parallel p-n layers 15 and a Schottky electrode 7. A p-high-resistance region 13 having a high resistance may be inserted between the p-column 10 and the electrode 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-breakdown-voltage, large-current-capacity super-junction diode, and more particularly to a super-junction shot having a special structure comprising a parallel pn layer which flows a current in an on state and depletes in an off state. Key diode.

[0002]

2. Description of the Related Art Generally, the forward characteristics of a diode are shown in FIG.
The characteristic diagram shown in FIG. The horizontal axis in this figure is the forward voltage, and the vertical axis is the current. The current does not flow until a certain rising voltage (built-in voltage), and the current starts to flow when biased further. The voltage at which a certain current is reached is called the on-voltage, and the slope of the voltage-current curve is called the on-resistance.

FIGS. 5A to 5C are sectional views showing the structures of various power diodes. FIG. 5 (a) shows the so-called p
(b) is a Schottky diode, and (c) is a diode of the fusion type. Each feature is as follows. In the pn diode of FIG. 5A, minority carriers can be injected from the p anode layer 2 into the n drift layer 3 to significantly reduce the electric conductivity of the n drift layer 3, so that the on-resistance is reduced. In addition, a large current can flow even with a high breakdown voltage diode. On the other hand, at the time of turn-off, the minority carriers injected from the n-drift layer 3 must be removed, which has a disadvantage that the switching speed is slow and the loss generated at that time becomes large.

In the Schottky diode of FIG. 5B, the Schottky electrodes 7 and n
The barrier height between the drift layers 3 can be controlled, so that the built-in voltage can be set low.
For this reason, a low breakdown voltage diode can realize a lower on-state voltage than a pn diode. Further, since there is no effect of accumulating minority carriers as in the case of a pn diode, there is a feature that the switching speed is high and the loss generated during switching is extremely small.

On the other hand, when a reverse voltage is applied, the barrier height of the Schottky electrode 7 and the semiconductor decreases, the leakage current in the reverse direction increases, and there is no conductivity modulation. There is a disadvantage that the ON resistance when a large current flows is increased. The on-resistance R _on A and the breakdown voltage V _B have the following relationship.

[0006]

(Equation 1) Here, μ is the electron mobility, ε is the dielectric constant of the semiconductor, and E _c is the maximum electric field strength.

As described above, when the breakdown voltage increases, the on-resistance rapidly increases. In FIG. 5B, the guard ring 6 is used.
It has. Although this is a p-type region, FIG.
Unlike the pn junction of (a), the pn junction is formed only at the periphery of the Schottky electrode 7 to prevent the electric field from concentrating around the Schottky electrode 7.

FIG. 5 shows a structure proposed to compensate for the disadvantages of both the pn diode and the Schottky diode.
(C) is a fused diode. The structure is such that an injection p region 8 for minority carrier injection is provided inside the Schottky electrode of FIG. 5B. By designing the dimensions of the implantation p region 8 according to the application, an optimal balance between the on-resistance and the switching loss can be realized.

On the other hand, in recent years, it has been found that a new junction structure can cause a breakthrough in lowering the on-resistance of a high breakdown voltage semiconductor device [EP0053854, US
P5216275, US Pat. No. 5,438,215 and JP-A-9-266311, Deboy, G. et al .: Technical Di
gest of IEDM '98, (1998), pp. 683 to 685]. In this structure, the drift layer is constituted by a parallel pn layer in which an n-type region and a p-type region with an increased impurity concentration are alternately arranged, and is depleted when off to bear a breakdown voltage. It is. Note that a semiconductor element including such a drift layer composed of a parallel pn layer is referred to as a super junction semiconductor element.

The applicant of the present invention also discloses Japanese Patent Application Laid-Open No. 2000-4082.
Japanese Patent Application Laid-open No. 2 (1994) proposes a simple method for manufacturing such a semiconductor device. In this structure, the relationship between the on-resistance R _on A and the breakdown voltage V _B is as follows [Fujihira, T:
Japanese J. of Appl. Phys. 36, (1997) 6254-62
See page 62].

[0011]

(Equation 2) Here, d is the width of the super junction.

That is, in the above equation (1), the on-resistance is proportional to the square of the withstand voltage. On the other hand, in the super-junction semiconductor element, the on-resistance is only proportional to the square of the withstand voltage. This shows that the resistance does not increase so much.
According to Fujihira's report, for example, in the case of a device with a withstand voltage of 1000 V, d = 5 μm, and the impurity concentration and the thickness of the epitaxial layer at this time are each 5 × 10 ¹⁵ c
Assuming m ⁻³ and 60 μm, the on-resistance is about 1/10
Down to.

Although a general Schottky diode often breaks down due to a current concentrated particularly on the terminal portion of the electrode, a Schottky diode using a super junction structure causes a current to flow along each column. Therefore, there is also an effect that local current concentration can be avoided.

[0014]

In response to a strong demand for reduction of switching loss and reduction of large noise generated at the time of switching, a problem is that a pn diode injecting minority carriers has large loss and large noise. There is. Originally, to reduce the switching loss, the Schottky diode of FIG. 5B is most preferable.

FIG. 7 shows an example of a super-junction type Schottky diode similar to that disclosed in Japanese Patent Application Laid-Open No. 2000-40822. 4 is a low resistance n ⁺ cathode layer, 1
5 is a parallel pn layer composed of an n drift region 9 and a p partition region 10. On the surface layer, an n ⁻ high resistance layer 11 is provided, a part of the p partition region 10 is exposed, and a Schottky electrode 7 that forms a Schottky barrier with the n ⁻ high resistance layer 11 is provided. . A cathode electrode 5 is provided on the back surface of the n ⁺ cathode layer 4.

However, as shown in equation (1),
Since it is essentially a Schottky diode, there is no injection of minority carriers as in a pn diode, and it is inevitable that the on-resistance rapidly increases in a large current region. However, the pn junction is partially biased at the time of forward bias, minority carrier injection occurs, and minority carrier injection occurs, thereby increasing the switching speed.

In view of the above problems, an object of the present invention is to provide a super-junction type Schottky diode which has a low on-resistance, does not have a forward biased pn junction, and can perform high-speed switching.

[0018]

In order to solve the above problems, the present invention provides a first conductive semiconductor layer having first and second main surfaces, a Schottky barrier electrode provided on one of the main surfaces, and A cathode electrode in ohmic contact with the other main surface,
A super-junction Schottky diode including a parallel pn layer in which first conductive type drift regions and second conductive type partition regions are alternately arranged between first and second main surfaces, wherein the Schottky electrode and the second It is assumed that a first conductive high resistance region having a higher specific resistance than the first conductive drift region is provided between the conductive region and the conductive partition region.

Since the pn junction is not forward-biased due to the presence of the first conductive high resistance region, minority carriers are not injected and high-speed switching is possible. In particular, the impurity concentration of the first conductive high resistance region is 1 × 10 ¹³ to 1 × 1.
It should be in the range of 0 ¹⁵ cm ^-3 . If the impurity concentration of the first conductive high-resistance region is too low, the resistance increases. Conversely, if it is too high, the leakage current at the time of reverse bias increases. Further, the impurity concentration of the first conductivity type high resistance region also affects the height of the Schottky barrier, so that it must be an appropriate concentration.

A super junction Schottky in which the Schottky electrode and the second conductive type partition region are at least partially electrically connected by the second conductive type high resistance region having a higher specific resistance than the second conductive type partition region. The same applies to diodes. In this case, the impurity amount of the second conductive type high resistance region is 1
It is assumed that it is in the range of × 10 ¹² to 1 × 10 ¹⁴ cm ^-2 .

The presence of the second conductive type high resistance region connected to the second conductive type partition region allows the potential of the Schottky electrode to be effectively transmitted to the second conductive type partition region. However, if the impurity concentration of the second conductive high resistance region is too low, the resistance increases, and the potential control of the second conductive partition region becomes insufficient. On the other hand, if it is too high, the injection of minority carriers is promoted during forward bias, and the switching speed is increased.

Further, it is preferable that the second conductivity type partition regions are electrically connected to each other. In such a super junction Schottky diode, the potential of the Schottky electrode is effectively transmitted, and the potential of the second conductivity type partition region becomes uniform.
Further, if the semiconductor is silicon carbide, a Schottky diode having a high breakdown voltage and a high temperature exceeding the range of the silicon semiconductor element can be obtained.

[0023]

FIG. 1 is a sectional view of a first embodiment of a super junction Schottky diode to which the present invention is applied. 4 is a low resistance n ⁺ cathode layer, and 15 is a parallel pn layer comprising an n drift region 9 and a p partition region 10. The n ⁻ high resistance layer 11 is provided on the parallel pn layer 15, and a Schottky electrode 7 for forming a Schottky barrier is provided on the surface thereof. A cathode electrode 5 is provided on the back surface of the n ⁺ cathode layer 4. In this example, the n ⁻ high resistance layer 1 is also provided between the parallel pn layer 15 and the n ⁺ cathode layer.
There are cases in which there is no such number. The Schottky electrode 7 is, for example, titanium (Ti).

FIG. 2A is a perspective plan view of the pattern of the parallel pn layer of the super junction Schottky diode of FIG. 1 as viewed from above. In this example, since the p-partition region 10 is columnar, it is called a p-column. Seen from above, it is cellular. For example, for a device with a withstand voltage of 1000 V, p
The width d of the column 10 is 5 μm. At this time, the impurity concentration and the thickness of the parallel pn layer 12 are 5 × 10 ¹⁵ cm ⁻³ and 60 μm, respectively.
m. When the width of the n drift region 9 is the same, the area is 3
Therefore, the impurity concentration may be reduced to 1/3. It is preferable that the n ⁻ high resistance layer 11 in contact with the Schottky metal 7 has a lower concentration than the n drift region 9 forming the parallel pn layer 15 in the substrate. This is to flatten the electric field in the vicinity of the surface to prevent generation of a leak current due to electric field concentration. Specifically, it is about 1 × 10 ¹³ to 1 × 10 ¹⁵ cm ⁻³ . The thickness is 0.5 to 10 μm.

As other examples, a houndstooth check pattern as shown in FIG. 2B and a stripe pattern as shown in FIG. 2C can be considered. In these cases, the impurity concentrations of the n drift region 9 and the p partition region 10 are made equal. FIG.
In the conventional super-junction Schottky diode described above, the p column 10 is short-circuited to the Schottky electrode 7, but in the super-junction Schottky diode of the present embodiment, this is not short-circuited. That is, the difference is that n ⁻ high resistance layer 11 is left between p column 10 and Schottky electrode 1.

When the device is configured in this manner, in the forward bias, a very low on-resistance unique to the super junction structure can be realized, and the injection of minority carriers from the p region such as the conventional super junction Schottky diode can be realized. Is not accompanied. Therefore, the reverse recovery time is 1/10 or less as compared with the conventional super junction Schottky diode shown in the figure, and high-speed switching can be realized.

FIG. 3 is a diagram showing the spread of the depletion layer when a reverse bias is applied to the super junction Schottky diode of the present invention. When a reverse bias is applied, the depletion layer 12
Spreads from the Schottky electrode 7 to the n ⁻ high resistance layer 11 and reaches the p column 10, the potential spreads to the entire parallel pn layer 15, and the depletion layer spreads as shown in FIG. Thus, sufficient breakdown voltage can be maintained even when p column 10 is not in contact with Schottky electrode 7. The depth from the surface to the p-column 10 of the super-junction structure has a close relationship with the withstand voltage and requires a design for each withstand voltage, but is about 0.5 to 5 μm.

A guard ring 6 similar to that of a conventional diode is provided around the Schottky electrode 7.
Other pressure-resistant structures conventionally used, such as a field plate, can also be used. Further, in FIG. 1, parallel pn is provided only in the active portion where the current below Schottky electrode 7 flows.
Although the layer 15 is provided, it may be extended to the peripheral withstand voltage structure. As the Schottky electrode, other commonly used Al, Mo, Ni, etc. can be used.

[Embodiment 2] FIG. 4 is a sectional view of a second embodiment of the present invention. The difference from the first embodiment shown in FIG. 1 is that a p-high resistance region 13 having a high resistance is partially added between the p column 10 and the Schottky electrode 1 so that the p
This is a point connected to a part of the column 10.

Since the p-high resistance region 13 has an effect of equalizing the potential of the p column 10, it is better to have a high impurity concentration to some extent. Conversely, if the impurity concentration is too high, minority carriers are injected. It is not possible to make the concentration too high. Therefore, the total amount of impurities in the p high resistance region 13 is 1 × 1
It is preferable to be about 0 ¹² to 1 × 10 ¹⁴ cm ⁻³ . The p-high resistance region 13 also has an effect of releasing an avalanche current generated at the pn junction, and is effective when the junction requires a large amount of resistance.

Further, in order to make voltage application and current sharing uniform among the p columns 10, a p connection region 14 for partially connecting the p columns 10 may be provided. [Embodiment 3] In the above embodiments, the case where silicon is used as the semiconductor material has been described. However, in recent years, it has been pointed out that when a power element is formed of silicon carbide, characteristics are significantly improved.

By applying the present invention to silicon carbide, a device having higher performance than silicon can be realized. In particular, when applied to silicon carbide, since the concentration of the p column and the n drift region can be set high, it can be used at a higher temperature. Further, in the crystal growth of silicon carbide, the impurity concentration that can be controlled is about 1 × 10 ¹⁵ cm ⁻³ , and with this concentration, the breakdown voltage is about 5 kV.
However, by using a super junction structure, the concentration of the p column and the n drift region can be increased by one digit or more. can do.

[0033]

As described above, according to the present invention, the first conductive type high resistance having substantially higher specific resistance than the first conductive type drift region between the Schottky electrode and the second conductive type partition region. By providing the region, a super-junction Schottky diode with a high switching speed could be obtained.
Of course, since it is a super-junction semiconductor element, the on-resistance is much lower than that of a normal Schottky diode. Therefore, a Schottky diode having low on-loss and switching loss can be realized.

Further, by providing a second conductive type high resistance region connected to the second conductive type partition region and a connection region connecting the second conductive type partition region, the potential of the second conductive type partition region is stabilized. As a result, destruction due to local current concentration can be avoided, and a highly reliable Schottky diode can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a super junction Schottky diode according to a first embodiment of the present invention.

FIG. 2A is a horizontal sectional view of a parallel pn layer portion of a super junction Schottky diode of Example 1, and FIGS. 2B and 2C are horizontal sectional views of a parallel pn layer portion of another super junction Schottky diode. Figure

FIG. 3 is a sectional view showing a depletion layer when a reverse voltage is applied to the super junction Schottky diode according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a super junction Schottky diode according to a second embodiment of the present invention.

5A is a sectional view of a pn diode, FIG. 5B is a sectional view of a Schottky diode, and FIG. 5C is a sectional view of a fusion diode.

FIG. 6 is a forward current-voltage characteristic diagram of a diode.

FIG. 7 is a cross-sectional view of a conventional super junction Schottky diode.

[Explanation of symbols]

1 anode 2 p anode region 3 n drift layer 4 n ⁺ cathode region 5 the cathode electrode 6 guard ring 7 Schottky electrode 8 implanted for the p region 9 n drift region 10 p drift region or p columns 11 n ^- high resistance region 12 depleted layer 13 p high resistance region 14 p connection region 15 parallel pn layer 16 n ^- high resistance region

Claims (6)

[Claims] A first conductive semiconductor layer having first and second main surfaces; a Schottky electrode provided on one of the main surfaces;
Super junction comprising a cathode electrode in ohmic contact with the other main surface, and a parallel pn layer between the first and second main surfaces, in which first conductive type drift regions and second conductive type partition regions are alternately arranged. In the Schottky diode, a superconductive junction having a first conductive high resistance region having a resistivity substantially higher than that of the first conductive drift region between the Schottky electrode and the second conductive partition region. Schottky diode 2. The method according to claim 1, wherein the impurity concentration of the first conductive high resistance region is 1 ×.
2. The super-junction Schottky diode according to claim 1, wherein the Schottky diode is in a range of 10 < ¹³ > to 1 * 10 < ¹⁵ > cm < ^-3 >. A first conductive semiconductor layer having first and second main surfaces; a Schottky electrode provided on one of the main surfaces;
Super junction comprising a cathode electrode in ohmic contact with the other main surface, and a parallel pn layer between the first and second main surfaces, in which first conductive type drift regions and second conductive type partition regions are alternately arranged. In the Schottky diode, the Schottky electrode and the second conductive type partition region are electrically connected at least in part by a second conductive type high resistance region having substantially higher specific resistance than the second conductive type partition region. A super junction Schottky diode, characterized in that: 4. The method according to claim 1, wherein the amount of impurities in the second conductive high resistance region is 1 × 1.
0¹²~ 1 × 10¹⁴cm ^-2The contract is characterized by being in the range of
The super-junction Schottky diode according to claim 3. 5. The super-junction Schottky diode according to claim 1, further comprising a connection region for electrically connecting the second conductivity type partition regions to each other. 6. The super-junction Schottky diode according to claim 1, wherein the semiconductor is silicon carbide.