JP3412283B2 - Semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device such as a diode used as a freewheel diode in an inverter or the like. 2. Description of the Related Art As the speed of switches used in inverters and the like has increased, fast recovery and soft recovery of diodes connected in antiparallel have been required. [0003] This is because if the loss per operation at the time of reverse recovery becomes large, it is impossible to operate at a high frequency, and if the reverse recovery current rise rate in the second half of the reverse recovery is high, a surge voltage is generated, and the element is deteriorated or deteriorated. It will be destroyed. [0004] Conventionally, in order to reduce the loss at the time of reverse recovery, electron beam irradiation or the like is used to shorten the life time of the element. The loss at the time of recovery can be reduced, but at the same time, the rate of increase of the reverse recovery current increases. This is because the accumulation speed near the junction of the diode affects the reverse recovery current increase rate, but if the lifetime is controlled by the electron beam, the lifetime in the entire region is shortened. The present invention has been made in view of the above problems, and an object of the present invention is to provide a highly reliable semiconductor device capable of reducing a loss at the time of reverse recovery without generating a large surge voltage. In order to achieve the above object, a semiconductor device according to the present invention comprises a first semiconductor layer and a second semiconductor layer having different polarities adjacent to each other, and First
The semiconductor layer and the cathode electrode and the shorted cathode layer,
In a semiconductor layer having an anode layer in which a second semiconductor layer is short-circuited with an anode electrode, a second layer forming the anode layer may be used.
Is formed in a waveform having a thick portion and a thin portion, and a third semiconductor layer having a polarity different from that of the second semiconductor layer is formed on a part of the second semiconductor layer forming the anode layer. Is provided in such a manner as to be short-circuited with the anode electrode, and the total amount of impurities of the second semiconductor layer immediately below the third semiconductor layer of the anode layer is (V) ^1/2 · (2 ε C _B / q) or more. There is a feature. However, V is required withstand voltage, epsilon is the dielectric constant of silicon, C _B is the average impurity concentration, q is the charge of an electron. As a method for increasing the annihilation rate of carriers near the junction, a P-type layer of the anode is formed in a waveform, and N is formed in a shallow portion thereof. This is a structure in which a mold layer is formed. At this time, the P-type layer immediately below the N-type layer is designed so that an electric field formed when a voltage is applied thereto does not reach the N-type layer. By forming the anode of the diode in this way, the accumulated carriers near the junction are quickly discharged to the anode electrode through the N-type layer at the time of reverse recovery, and the junction recovery time at the beginning of reverse recovery can be shortened. it can. An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view of a diode as a semiconductor device according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an N-type semiconductor layer (N ⁻ layer) serving as a semiconductor substrate, and 2 denotes N ^−.
A high impurity concentration N-type semiconductor layer (N ⁺ layer) which is formed on one main surface of the layer 1 and forms a cathode layer. Reference numeral 3 denotes a P-type semiconductor layer (P) formed on the other main surface of the N ⁻ layer 1.
Mold layer) to form an anode layer. 5 is an anode electrode and 6 is a cathode electrode. The feature of this embodiment is that, as shown in FIG. 1, the P-type layer of the anode is formed so as to have a corrugated cross section, and the P-type layer 3 is formed in a shallow portion of the P-type layer 3. The mold layer 3 means that an N-type semiconductor layer (N-type layer) 4 having a different polarity is formed. FIG. 2 shows the concentration profile and the electric field distribution of the diode according to this embodiment. As shown in FIG.
The total amount of impurities in the P-type layer 3 immediately below the N-type layer 4 in the anode layer is determined by (V) ^1/2 · (2 ε C _B ) in order to obtain a required breakdown voltage.
/ Q) to be present at least ^1/2 . Here, V is the required breakdown voltage, epsilon is permittivity of silicon, C _B is the average impurity concentration, q is the charge of an electron. The P-type layer 3 immediately below the N-type layer 4 needs to be designed so that the electric field applied thereto does not reach the N-type layer 4. By forming the anode of the diode in this manner, the accumulated carriers near the junction are quickly discharged to the anode electrode 5 through the N-type layer 4 at the time of reverse recovery, and the junction recovery time at the initial stage of reverse recovery is shortened. FIG. 3 shows a diode as a semiconductor device according to a second embodiment of the present invention. In the diode of this embodiment, the P-type layer 3 of the anode layer is formed in a wave shape, The N-type layers 4 and 4 are provided adjacent to the protrusion 3a of FIG. 1, and the anode electrode 5 is provided so that the P-type layer 3 and the N-type layers 4 and 4 are short-circuited. Functions and effects can be obtained. The above embodiments are summarized as follows. (A). The anode layer of the diode is formed in a waveform. (B). An N-type layer is provided on a part of the corrugated anode layer in the section (A). (C). The electrodes are formed such that the P-type portion and the N-type portion of the anode layer in the item (B) are short-circuited. (D). (A), occurs more than (B) or (C) required √V · √ for total impurity amount of the P-type layer immediately below the N-type layer of the anode layer to obtain a breakdown voltage section (2 ε C _B / q) A diode characterized by the above. Where V is the required breakdown voltage, ε
The dielectric constant of silicon, C _B is the average impurity concentration, q is the charge of an electron. According to the present invention, as described above, basically, a first semiconductor layer and a second semiconductor layer having different polarities are formed adjacent to each other, In the semiconductor layer in which the semiconductor layer is a cathode layer and the second semiconductor layer is an anode layer, the second semiconductor layer forming the anode layer is formed in a waveform having a thick portion and a thin portion.
The junction recovery time is shortened without increasing the reverse recovery current increase rate, and the loss at the time of reverse recovery can be reduced without generating a large surge voltage.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view of a diode according to a first embodiment of the present invention. FIG. 2 is a diagram showing a concentration profile and an electric field distribution of a diode according to a first embodiment of the present invention. FIG. 3 is a schematic sectional view of a diode according to a second embodiment of the present invention. [Description of Reference Numerals] 1 ... semiconductor substrate N ^- type semiconductor layer 2 ... N ⁺ -type semiconductor layer 3 ... P-type semiconductor layer 4 ... N-type semiconductor layer 5 ... anode electrode 6 ... cathode electrode

Claims (1)

(57) [Claim 1] A first semiconductor layer and a second semiconductor layer having different polarities are formed adjacent to each other, and the first semiconductor layer is
In a semiconductor layer in which a cathode layer is short-circuited to a cathode electrode and a second semiconductor layer is an anode layer short-circuited to an anode electrode, the second semiconductor layer forming the anode layer has a waveform having a thick portion and a thin portion. A third semiconductor layer having a polarity different from that of the second semiconductor layer is provided on a part of the second semiconductor layer forming the anode layer so as to be short-circuited with the anode electrode. The total amount of impurities in the second semiconductor layer immediately below the third semiconductor layer is (V) ^1/2 · (2
wherein a being present ε C _B / q) above. However, V is required withstand voltage, epsilon is the dielectric constant of silicon, C _B is the average impurity concentration, q is the electron charge quantity.