JPH06163948A - Semiconductor diode - Google Patents

Abstract

PURPOSE:To obtain a semiconductor device wherein the backward leakage current is small, and the voltage drop in the forward direction is small. CONSTITUTION:The semiconductor device consists of a bulk barrier diode region having 4-layered structure and a semiconductor region 5. The diode region is composed of a semiconductor region 1 of high impurity concentration which turns to a main current flow region, a semiconductor region 2 of low impurity concentration, a semiconductor region 3 in which a barrier for majority carrier exists in the thermal equilibrium depletion state, and a semiconductor region 4 of high impurity concentration. The semiconductor region 5 is formed to decrease the ON-voltage and increase the withstand voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor diode having a small forward voltage drop and a fast switching operation.

[0002]

2. Description of the Related Art In a situation where the operating voltage of a VLSI circuit is being reduced, there is a demand for reducing the forward voltage drop of an output diode used in a switching power supply to reduce the loss. As a device capable of operating at a high speed and realizing a low on-voltage as compared with a silicon diode having a rising voltage of about 0.7 V, there is a majority carrier diode in which a current is transported by a majority carrier. It can operate at high speeds because there is no minority carrier accumulation, and has a small voltage drop because current transport is not limited by minority carrier diffusion. There is a Schottky barrier diode as a power semiconductor device which has been put into practical use as such a majority carrier diode. However, in order to reduce the forward voltage drop, the height of a potential barrier (hereinafter referred to as a barrier) is reduced. However, there is a problem that the reverse leakage current increases and the size of the barrier is determined by the metal material. Furthermore, vertical M
Synchronous rectifier diodes, which are made into diodes by using OSFETs, can have considerably lower on-voltage than silicon diodes and Schottky barrier diodes.
This device has a problem that a control gate signal for synchronization for rectification is required.

In recent years, a bulk unipolar device in which a barrier for majority carriers is formed inside a semiconductor bulk by controlling the impurity density of a thin semiconductor layer (several tens of nm) with a steep profile by using an ion implantation technique or a molecular beam epitaxy technique. Devices collectively called diodes (camel diode, triangle barrier diode, p-plane diode, etc.) have been proposed. These devices have a feature that the height of the barrier can be freely controlled by the thickness of the semiconductor layer and the impurity density. However, these devices require control of a fairly thin semiconductor layer of several tens of nanometers, and the reverse breakdown voltage becomes considerably smaller as the forward-direction rising voltage is made smaller, and both low forward voltage and high reverse breakdown voltage are compatible. difficult.

This bulk unipolar diode will be described in more detail with reference to FIG. 4, which is an N-conductivity type semiconductor region 1 having a high impurity concentration and a N-conductivity type semiconductor region 2 having a low impurity concentration, which are main current passage regions. ,
A four-layer structure including a P-conductivity type semiconductor region 3 having a high impurity concentration and an N-conductivity type semiconductor region 4 having a very high impurity concentration, and formed in the first semiconductor region 1 and the fourth semiconductor region 4, respectively. A cathode electrode K and an anode electrode A are provided. Here, the third semiconductor region 3 has a higher impurity concentration than that of the second semiconductor region 2, and its thickness is considerably thin as several tens nm as described above. Then, a first junction J1 is formed between the first semiconductor region 1 and the second semiconductor region 2, and a second junction J2 is formed between the second semiconductor region 2 and the third semiconductor region 3. However, the third semiconductor region 3 and the fourth semiconductor region 3
A third junction J3 is formed between the semiconductor region 4 and the semiconductor region 4. This diode is characterized in that the thin semiconductor region 3 is in a thermal equilibrium state and is depleted due to the formation of the space charge layer of the junction J2 and the junction J3.
The barrier formed inside can be set mainly by the impurity density of the semiconductor region 3 and its thickness.

The forward direction of this diode is referred to as the first direction here.
In the case of injecting majority carriers of the first semiconductor region 1 from the semiconductor region 1 side toward the fourth semiconductor region 4,
The opposite direction is from the fourth semiconductor region 4 side to the first semiconductor region 1
It is assumed that the majority carriers of the fourth semiconductor region 4 are injected toward. In the forward bias state, the junction J
1 and J2 are forward biased, the junction J3 is reverse biased, and the applied voltage is shared by the three junctions. The current conduction mechanism is
This is mainly due to the mechanism in which the barrier is lowered in J2, which is a forward bias junction, and the majority carriers are injected. Although the forward voltage drop of this diode is relatively small, the forward voltage drop as a device includes not only the forward bias junction but also the reverse bias junction J3. There is also the problem that it will become larger.

Regarding the reverse bias, the conduction mechanism is exactly the same as the forward direction, but the reverse bias voltage is mainly
It becomes easier to apply the voltage to the reverse bias junction J2 having the low-impurity-concentration semiconductor region 2 having a high resistance in the neutral region, and the voltage is less likely to be applied to the forward-biased junction J3 as compared with the case of the forward direction. Therefore, the conduction start voltage in the reverse direction is somewhat larger than that in the forward direction, and the reverse breakdown voltage is provided to some extent, so that the rectifying property is provided. However,
It is difficult to increase the conduction start voltage in the reverse direction, and if the breakdown voltage in the reverse direction is increased, the rise voltage in the forward direction also increases. As described above, with only the four-layer bulk barrier diode structure, it is difficult to reduce the forward voltage drop because there is the junction J3 that is reverse-biased in the forward direction, and the reverse breakdown voltage is increased. However, since the sacrifice occurs in the forward direction and the forward voltage drop increases, it is difficult to achieve both low on-voltage and high reverse breakdown voltage.

In addition to the above, a semiconductor diode (Publication of Japanese Patent Application Laid-Open No. 58-60577) in which a reverse breakdown voltage is improved by adopting a pinch-off structure, or chip utilization efficiency and a low impurity layer are used for pinch-off. Schottky barrier diode designed to improve reverse breakdown voltage (Japanese Patent Laid-Open No. 2-151
No. 067), or a semiconductor diode employing an electrostatic induction structure to improve forward characteristics (Japanese Patent Laid-Open No. 4-84).
No. 466). The problems with these proposed semiconductor diodes will be described. In the former two proposals, since the pinch-off mechanism is adopted,
Although improvement of breakdown voltage can be expected, P is used as a barrier.
N-junction or Schottky barrier is used,
The barrier is determined by the material, and it is difficult to reduce the on-voltage. The remaining latter is a static induction transistor (hereinafter,
SIT) structure of a diode. The gate of the SIT is intended for the rectification effect by using the effect of relaxing the pinch-off of the channel in the forward direction and increasing the pinch-off in the reverse direction. In this case, if the pinch-off is not almost completely performed in the equilibrium state of the bias voltage of 0 V, there is a problem that the reverse current increases, but on the other hand, if the pinch-off is too strong, the on-voltage increases and the low on-voltage decreases. And a small reverse leakage current at the same time are difficult to manufacture. In the diode of the present invention, since the barrier height of the bulk barrier structure can be freely set, a low on-voltage can be achieved, and since the bulk barrier structure has a certain withstand voltage in the reverse direction as well, the pinch-off in the reverse direction is near 0V. It is not necessary to start from the beginning, thus facilitating the production.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a semiconductor diode having a small reverse leakage current and a small forward voltage drop.

[0009]

A semiconductor diode according to the present invention has a semiconductor region 1 having a high impurity concentration, which is a main current passage region, a semiconductor region 2 having a low impurity concentration, and a semiconductor region which is depleted in a thermal equilibrium state to absorb majority carriers. In addition to a bulk barrier diode region having a four-layer structure including a semiconductor region 3 having a barrier and a semiconductor region 4 having a high impurity concentration, a semiconductor region 5 is provided for achieving both low on-voltage and high breakdown voltage. At the same time, the semiconductor region 5 and the semiconductor region 4 are electrically short-circuited.

[0010]

1 is a sectional view showing the basic principle of a semiconductor diode according to the present invention. The semiconductor diode according to the present invention includes semiconductor regions 1, 2, 3, which are main current passage regions.
In addition to the bulk barrier diode region having a four-layer structure of 4, the semiconductor region 5 is provided so as to sandwich the bulk barrier diode narrowly in order to reduce the on-voltage and the high breakdown voltage. The same electrode 5 is electrically short-circuited. Then, as in the case of a normal bulk unipolar diode, the semiconductor region 3 is depleted in a thermal equilibrium state, and a majority carrier barrier exists in the semiconductor region 3. The difference from the conventional bulk barrier diode is that
By adjusting the impurity density of the semiconductor regions 2 and 3,
Depletion can be achieved with a thickness that is relatively easy to control, and by providing the semiconductor region 5 and electrically short-circuiting the semiconductor region 4 and the semiconductor region 5, a low on-voltage and an improvement in reverse breakdown voltage can be achieved. It is in. The semiconductor diode of the present invention is provided with an electrode E1 in the first semiconductor region 1 and an electrode E2 across the fourth semiconductor region 4 and the fifth semiconductor region 5 to short-circuit these regions.

First, the diode operation that overcomes the above problems will be described. The directions of carrier injection for forward and reverse operation of this diode are the same as those of the above-mentioned four-layer bulk unipolar diode. In the forward direction, since the semiconductor region 5 and the semiconductor region 4 are short-circuited at the electrode E2, the reverse-biased junction J3 is short-circuited, and unlike the above-mentioned four-layer bulk unipolar diode, a reverse-biased junction exists. Disappear. To that extent, the forward voltage drop is reduced, and a low on-voltage can be achieved.
Moreover, when the applied voltage in the forward direction is increased, 0.7 V
Above a certain level, the second semiconductor region 2 and the fifth semiconductor region 5
The junction J4 between and also becomes conductive, and carriers in the semiconductor region 5 start injection, which is also suitable for increasing the current.

In the diode of the present invention, there are two junctions that are reverse biased in the reverse direction, one is the junction J2 of the bulk barrier region and the other is the junction J4 formed by the semiconductor region 5. . As long as the reverse direction applied voltage is small, in the bulk barrier diode region, the voltage tends to be applied to the junction J3 which is forward biased in the reverse direction in the direction of lowering the barrier. Since the semiconductor region of the high resistivity layer is provided in the neutral region, almost no applied voltage is applied to the junction J2, so that the reverse leakage current does not occur. As the reverse voltage is increased, the junction J3 also shares the voltage to lower the barrier, and the reverse leakage current tends to start flowing. Therefore, with the conventional bulk barrier diode structure alone,
Only a certain reverse breakdown voltage can be expected. In the diode according to the present invention, when the junction J3 is about to start decreasing, the depletion layer extends from the other reverse bias junction J4 to electrostatically shield the junction J3, and a voltage is applied to the junction J3. Since it works so as not to be prevented and the barrier lowering is suppressed, the reverse leakage current from the junction J3 is hard to occur, and the reverse breakdown voltage is significantly improved. Therefore, the semiconductor diode according to the present invention can achieve a high breakdown voltage while achieving a low on-voltage. Further, in principle, since the majority carriers are conducted by lowering the barrier, high speed operation is possible.

Next, one embodiment of a concrete semiconductor diode according to the present invention will be described with reference to FIG. Figure 2
It is an embodiment in which the conduction carrier of the bulk unipolar diode portion according to the present invention is an electron. In FIG. 2, N _S ⁺ region 1, N _B ⁻ region 2 and N _D ⁺ region 4 are n
Shaped semiconductor regions, which respectively correspond to the semiconductor regions 1, 2, 4 in FIG. The P _B ⁻ region 3 is a p-type semiconductor region, is depleted in the thermal equilibrium state, and corresponds to the semiconductor region 3 in FIG. The P _B ⁺ region 5 has the same conductivity type as the P _B ⁻ region 3 having a low impurity concentration and is a high impurity density region, and corresponds to the semiconductor region 5 of FIG. Further, a cathode electrode K is formed in the N _S ⁺ region 1, and an anode electrode A is formed in the N _D ⁺ region 4 and the P _B ⁺ region 5 so as to short-circuit these semiconductor regions. In this figure, one P _B ⁻ region 3, N _D ⁺ region 4 and one P _B ⁺ region 5 are shown for the sake of simplicity, but in an actual device, these semiconductor regions are formed in stripes. Alternatively, it is often formed in a grid or island shape.

In manufacturing, the resistivity is 0.005Ω
cm with a high impurity density n of about 400 μm
Type N ⁺ substrate with the same conductivity type and a resistivity of 5
P ⁻ / N ⁻ / N ⁺ was formed by epitaxially growing an N ⁻ layer having a thickness of about 0 Ωcm and a thickness of about 20 μm, and then epitaxially growing a P ⁻ layer of p-type semiconductor having a resistivity of about 10 Ωcm and a thickness of about a few μm. A substrate is used. N ⁺ substrate,
The N ⁻ layer and the P ⁻ layer correspond to N _S ⁺ region 1, N _B ⁻ region 2 and P _B ⁻ region 3, respectively. Using this substrate, P
_{From the B} ⁻ region 3 side, p-type selective diffusion is performed so as to leave a gap having a width of about 5 to 10 μm in the central portion, and the P _B ⁺ region 5 has a surface density of about 10 ¹⁹ cm ⁻³ and a diffusion depth of about 5 μm. , N
_B ⁻ Formed to extend to region 2. That, P _B ^- region 3 N _B ^- than the junction J2 to form the region 2, P _B ⁺ regions 5 N _B ^- joined to form the region 2 J4 is N _B towards (almost parallel to the junction J2) ^- to be formed in a deep position of region 2 performs a p-type selective diffusion. This deep P _B ⁺ region 5 makes it possible to achieve the electrostatic shielding effect of the junction J3 in the reverse direction of the diode according to the invention. Further, N _B ^- by the low impurity concentration region 3, P _B ^{- -} the impurity concentration of the region 2 P _B ^- lower than the region 3, and P _B can be relatively thicker regions 3 Yes, this facilitates fabrication.

Next, finally, n having a surface density of about 10 ²⁰ cm ^{-3 is} formed so as to have a width approximately equal to or slightly larger than the gap between the two P _B ⁺ regions 5 and cover the gap. Shape selective diffusion is performed to form N _D ⁺ regions 4. This N _D ⁺
The depth of the region 4 is set so that the remaining P _B ⁻ region 3 has a thickness capable of being depleted in a thermal equilibrium state. By using the double epitaxial substrate, the impurity density of the P _B ⁻ region 3 can be lowered, so that depletion is easy, and the final thickness of the P _B ⁻ region 3 can be controlled relatively easily to 0. It can be realized in about 2 μm. The barrier of electrons formed in the depleted P _B ⁻ region 3 can be made smaller than that of a normal Schottky barrier by forming the P _B ⁻ region 3 thin, and 0.3 V or less is expected. it can. By providing the cathode electrode K and the anode electrode A after the above diffusion process, a semiconductor diode can be realized in which the conduction carrier of the bulk unipolar diode portion of the present invention is an electron. Needless to say, even when the conductivity types of all the above-mentioned regions are reversed, a semiconductor diode in which the carriers of the bulk unipolar diode portion of the present invention are holes is realized. Further, in this embodiment, the P ⁻ / N ⁻ / N ⁺ epi growth substrate was used,
It can be realized even if the P ⁻ layer is formed by ion implantation.

Next, the operation of the semiconductor diode having such a configuration will be described. The forward direction of the diode is the case where a negative polarity voltage is applied to the cathode electrode K and the positive polarity voltage is applied to the anode electrode A, and the reverse direction is the case where the polarity of the applied voltage is reversed. Anode electrode A allows N _D ⁺ region 4 and P
Because the _B ⁺ area 5 are short-circuited, in the forward direction, is short-circuited junction J3 to the junction of the reverse bias, applied voltage is applied to the junction of the forward bias J1, and junction J2, P _B ^- region 3 has a thickness capable of being depleted in a thermal equilibrium state, the barrier of P _B ⁻ region 3 is lowered by a slight applied voltage, for example, an applied voltage of about 0.3 V, and N _S
⁺ Electrons from the region 1 are injected to start conduction. Furthermore, when the applied voltage increases and 0.7 V or more, P _B ⁺
Since injection of holes from the junction J4 formed by the region 5 and the N _B ⁻ region 2 is also added, a large current can be achieved.

In the reverse direction, the junction J4 and the junction J2 are reverse bias junctions. However, as long as the reverse bias voltage is relatively small, the forward bias junction J3 of the bulk barrier diode section receives little voltage. , The barrier is not lowered and therefore the reverse leakage current is very small. When the reverse bias voltage is increased, a voltage is applied to the forward-biased junction J3, and a reverse leakage current tends to flow due to the barrier lowering, but the anode electrode A causes the N _D ⁺ region to flow. 4 and the P _B ⁺ region 5 are short-circuited, the depletion layer extending from the junction J4 into the N _B ⁻ region 2 electrostatically shields the junction J3 by the electric field and suppresses the barrier lowering of the junction J3. Therefore, generation of a leak current from the junction J3 is prevented, and thus the breakdown voltage is significantly improved.

Next, FIG. 3 shows an embodiment of another more specific semiconductor diode according to the present invention. This is because an N ⁻ semiconductor region 2, a P ⁻ semiconductor region 3, and an N ⁺ semiconductor region 4 are sequentially formed on an N ⁺ type semiconductor substrate 1 by epitaxy, and then a commonly used unidirectional etching technique is used. The grooves extending from the surface of the N ⁺ semiconductor region 4 to the inside of the N ⁻ semiconductor region 2 in a grid pattern or a stripe pattern,
Alternatively, a plurality of island-shaped trenches are formed, P-type impurities are implanted through these trenches to form P ⁺ semiconductor regions 5 along the trench walls, and then these trenches are filled with a conductive material 6 such as a polycrystalline semiconductor material. The anode electrode A is uniformly formed on the surface of the N ⁺ semiconductor region 4, the P ⁺ semiconductor region 5 and the conductive material 6 with a metal material such as aluminum. The dimensions such as impurity concentration and size of each semiconductor region are shown in Fig. 2.
It may be carried out according to the embodiment of. In this embodiment, since the semiconductor regions 2, 3 and 4 can all be formed by epitaxial growth, the number of subsequent heat treatments can be small, and therefore the desired thin P ^- semiconductor region 3 can be obtained. In the embodiment shown in FIGS. 2 and 3,
A semiconductor diode having a similar effect can be obtained by reversing the conductivity type of each semiconductor region.

[0019]

As described above, according to the present invention, it is possible to obtain a bulk unipolar semiconductor diode which has a small reverse leakage current and a small forward voltage drop and which is relatively easy to manufacture.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a basic description of a bulk unipolar semiconductor diode according to the present invention.

FIG. 2 is a view showing an embodiment in which a conduction carrier of a bulk unipolar semiconductor diode according to the present invention is realized as an electron.

FIG. 3 is a view showing another embodiment of a specific semiconductor diode according to the present invention.

FIG. 4 is a view showing a conventional bulk unipolar diode type semiconductor device.

[Explanation of symbols]

1, 2, 5 ... Semiconductor regions of the first conductivity type (corresponding to N _S ⁺ , N _B ⁻ , and N _D ⁺ in order in FIG. 2) 3, 4 ... What is the first conductivity type Opposite second conductivity type semiconductor region (corresponding to P _B ⁻ and P _B ⁺ in sequence in FIG. 2) E1, K ... Electrodes A and E2 provided on semiconductor region 1 ... Semiconductor region 4 Provided electrode

Front Page Continuation (72) Inventor Yasuo Hasegawa 1-1-18 Takada, Toshima-ku, Tokyo Within Origin Electric Co., Ltd. (72) Hideo Yamaguchi 1-1-18 Takada, Toshima-ku, Tokyo Origin Electric Co., Ltd. In the company

Claims (1)

[Claims] 1. A junction J1 is formed between a first conductivity type semiconductor region 1 having a first electrode formed on one principal surface side and the other principal surface side of the semiconductor region 1. Conductive type semiconductor region 2, one main surface side forms a junction J2 with the semiconductor region 2 and a second conductive type semiconductor region 3 opposite to the first conductive type, and the second electrode is Of the first conductivity type semiconductor region 4 formed on the main surface side of the semiconductor region 3 and having the other main surface side forming a junction J3 with the other main surface side of the semiconductor region 3, and the second electrode. The semiconductor region 1 is formed and electrically short-circuited with the semiconductor region 4 by this electrode, and the semiconductor region 2 and the second conductivity type semiconductor region 5 forming the junction J4 are provided at a position deeper than the junction J2. The semiconductor region 2 has a high impurity concentration, and the semiconductor region 2 has a lower impurity concentration than the semiconductor region 3. 3 is in a thermal equilibrium state, and the joint J2 and the joint J
The semiconductor diode is characterized in that the semiconductor region 4 has a high impurity concentration and the semiconductor region 5 has a high impurity concentration.