JPH06260631A - Semiconductor device - Google Patents

Abstract

PURPOSE:To provide a high-speed device without marring the performance of on-voltage by constituting a high-resistivity area, which becomes the current path provided between a cathode area and an anode area, of a material high in maximum electric field power. CONSTITUTION:A surface gate type electrostatic thyristor is equipped, on one side of an n-type semiconductor substrate 11, with an n<+>-type cathode region 12, and, on the other side, with a p<+>-type anode area. Besides, this is equipped, between the cathode area 12 and the anode area 13, with an n<->-type high resistivity area 14 to become a current path, and the current flowing in this high resistivity area 14 is controlled with a p<+>-type gate area 15. Here, the high resistivity area 14 is constituted of SiC or diamond being the material high in maximum electric field power. Hereby, the thickness of the high resistivity area can be thinned, and the series resistance at conductivity can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bipolar power semiconductor device such as an electrostatic induction thyristor.

[0002]

2. Description of the Related Art FIG. 2 shows such a conventional electrostatic induction thyristor, in which an N ⁺ type cathode region 2 is provided on the front surface of an N ⁻ type semiconductor substrate 1 and a P ⁺ type anode region 3 is provided on the back side thereof. The current flowing between the anode and the cathode is controlled by the P ⁺ type region 4 called a gate. In addition, the static induction thyristor is a normally-on type in which current flows even if no signal is input to the gate region, and a normally-on type in which no current flows unless a signal is input to the gate region.
There is an off type. Here, the operation of a normally-off type electrostatic induction thyristor will be described.

In a normally-off type electrostatic induction thyristor, a depletion layer spreads in front of the channel which is a current path, and this depletion layer must be removed to turn it on. Therefore, when a positive voltage is applied to the gate region to remove the depletion layer, the anode and cathode operate as a PN diode. On the contrary, in order to turn it off, the gate voltage may be set to zero or a negative voltage may be applied to the gate to expand the depletion layer in front of the channel.

[0004]

However, in a bipolar device such as an electrostatic induction thyristor, at the time of turn-off, due to the effect of accumulating minority carriers, a current waveform with a tail is drawn, and a loss in switching becomes large. There is a problem. Therefore, in order to control the lifetime of minority carriers, there is a movement to increase the speed by methods such as heavy metal diffusion and ion irradiation. However, in the conventional structure, the thickness of the high specific resistance region must be increased in order to increase the breakdown voltage, resulting in an increase in the on-voltage.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor device capable of speeding up without impairing the performance of the on-voltage.

[0006]

In order to solve the above-mentioned problems, the present invention provides a cathode region on one side of a semiconductor substrate and an anode region on the other side, and between the cathode region and the anode region. In a semiconductor device having a high resistivity region serving as a current path, and a gate region controlling a current flowing through the high resistivity region, the high resistivity region is made of a material having a high maximum electric field strength (for example, SiC or diamond). Etc.), and is characterized in that lifetime control by heavy ion irradiation is applied to the front surface of the anode region.

[0007]

As described above, by forming the high specific resistance region, which has been conventionally provided with the withstand voltage, with SiC, diamond or the like having a high maximum electric field strength, the thickness of the high specific resistance region can be reduced, and as a result, the bipolar region can be thinned. It is possible to perform heavy ion irradiation on the front surface of the anode junction, which is effective for increasing the speed in a semiconductor device of the system.

In the conventional example, since the high specific resistance region is thick, it is difficult for heavy ions to reach the front surface of the anode junction.
It has to be set to 0 MeV to 20 MeV), which is not realistic in view of the device, the crystallinity of the irradiation object, and the like.

On the other hand, according to the present invention, heavy ion irradiation can be performed with a relatively low acceleration energy (several MeV), and the saturation speed, which is a physical property of SiC or diamond used in the high resistivity region, can be increased. By utilizing the largeness, the switching speed of the semiconductor device, especially the turn-off time can be greatly reduced. As a result, the loss can be reduced and the device can be downsized.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention and is a sectional view of a unit cell of a semiconductor device. The semiconductor device according to the present embodiment is a surface gate type electrostatic induction thyristor, which includes an N ⁺ type cathode region 12 on one side of an N ⁻ type semiconductor substrate 11 and a P ⁺ type anode region 13 on the other side. An N ⁻ -type high resistivity region 14 is provided between the cathode region 12 and the anode region 13 and serves as a current path, and a P ⁺ -type gate region 15 for controlling the current flowing through the high resistivity region 14 is provided. I have it. In FIG. 1, 16 is a cathode electrode, 17 is a gate electrode, and 18
Is an oxide film.

The high resistivity region 14 is made of SiC or diamond which is a material having a high maximum electric field strength. As a result, the Si material is used in the conventional example, and the thickness is 100 in the case of a product having a withstand voltage of 1000 V, for example.
It is necessary to have a size of at least μm, but by using a material having a maximum electric field strength of about 10 times,
The thickness of 4 can be reduced to about 1/10.

In the conventional structure, ion irradiation has been performed in order to speed up the semiconductor device, and the range of irradiation has been set to the front surface of the anode region 3. For this, a range of about 100 μm has been obtained by using light ions called protons. However, for speeding up, it is important to use ions having a larger mass than protons, which are light ions, because deep levels that form recombination centers effective for speeding up can be formed.

Range of protons, which are light ions, 100 μm
In order to obtain, the acceleration energy of ion irradiation is about 4 MeV
However, when it comes to heavy ions, enormous acceleration energy is required to obtain a range of about 100 μm, which is not realistic considering an accelerator. Also, 100
Irradiating heavy ions with a thickness of μm is not good considering the crystallinity of the semiconductor.

Therefore, by using a material that can make the thickness of the high resistivity region 14 about 10 μm in order to obtain a withstand voltage of about 1000 V, it is possible to enable heavy ion irradiation required for high speed. Here, heavy ions are
N (nitrogen), O (oxygen) and the like. In FIG. 1, 19 is a heavy ion irradiation region.

Next, the manufacturing process of the semiconductor device according to this embodiment will be briefly described. First, a different type of semiconductor material (Si, which has a high maximum electric field strength, is formed on a P ⁺ -type silicon wafer.
C, diamond, etc.) is grown. For example, in the case of SiC, a required film thickness corresponding to the breakdown voltage is formed by a sublimation method or a CVD (chemical vapor deposition) method. Then, after forming an oxide film, a gate region and a cathode region are sequentially formed. Then, an electrode is formed, and heavy ions are irradiated from the surface side so as to reach the anode junction surface.

In this way, for example, S is added to the high resistivity region 14.
By using iC, the recombination lifetime τ, which is an important parameter for increasing the carrier speed, is τ = 1 / ( _{NSV TH} ) (N: density, S: capture cross section, V _TH : thermal velocity) In, the density N can be doubled by irradiating heavy ions, and the thermal speed V _TH can be doubled by using SiC. That is, the recombination life of carriers can be increased to 1 / 5.4 times. This means that the fall time in the turn-off process becomes 1 / 5.4 times.
In this way, high-speed operation of the semiconductor device can be realized.

The present invention is not limited to the above embodiment. Although the surface gate type static induction thyristor is shown in the above embodiment, a buried gate type static induction thyristor may be used. The semiconductor device may be other than the static induction thyristor, and may be, for example, an IGBT (insulated gate bipolar transistor) or a gate turn-off thyristor. Furthermore, N and P of each conductivity type in the diffusion region may be reversed.

[0018]

As described above, in the semiconductor device according to the present invention, the high specific resistance region, which was conventionally made of Si (silicon), is made of a material having a high maximum electric field strength (for example, SiC, diamond, etc.). As a result, the thickness of the high specific resistance region can be reduced, and the series resistance during conduction can be reduced.

Further, since the thickness of the high-resistivity region can be made thin, heavy ion irradiation to the front surface of the anode junction, which is effective for speeding up in a bipolar semiconductor device, becomes possible. Therefore, according to the second aspect of the present invention, high-speed switching is possible, and in particular, the fall time at turn-off can be shortened and the switching loss can be reduced. As a result, the heat generation of the semiconductor device can be suppressed, and the equipment to be incorporated can be downsized.

[Brief description of drawings]

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

FIG. 2 is a sectional view showing a conventional example.

[Explanation of symbols]

 11 semiconductor substrate 12 cathode region 13 anode region 14 high resistivity region 15 gate region 16 cathode electrode 17 gate electrode 18 oxide film 19 heavy ion irradiation region

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 29/804

Claims (2)

[Claims] 1. A semiconductor substrate having a cathode region on one side, an anode region on the other side, and a high resistivity region serving as a current path between the cathode region and the anode region. A semiconductor device having a gate region for controlling a current flowing through a specific resistance region, wherein the high specific resistance region is made of a material having a high maximum electric field strength. 2. A semiconductor substrate having a cathode region on one side, an anode region on the other side, and a high specific resistance region serving as a current path between the cathode region and the anode region. In a semiconductor device having a gate region for controlling a current flowing through a specific resistance region, the high specific resistance region is made of a material having a high maximum electric field strength, and lifetime control by heavy ion irradiation is performed on the front surface of the anode region. A semiconductor device characterized by the above.