JPS5931993B2 - semiconductor rectifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure of a highly reliable power diode that is fast and has a low forward potential drop.

Demand for high-speed, low-loss power diodes for stabilizing power supplies for computer terminal equipment and the like is increasing. Conventionally, in order to obtain a high-speed diode, high speed has been achieved by adding an impurity such as gold to a pn junction diode that becomes a recombination center (lifetime killer) to shorten the lifetime of minority carriers. However, this method has the disadvantage that the bulk resistance of the semiconductor layer into which the lifetime killer is introduced increases, and the forward potential drop across the diode increases. This not only increases the power loss of the diode, but also increases Joule heat generation, which increases the size of the cooling fins and increases costs. To solve these problems, a so-called Schottky barrier diode using a metal-semiconductor contact rectifying layer is known as a high-speed and low-loss diode. However, this Schottky barrier diode has disadvantages in that its reverse leakage current is three orders of magnitude larger than that of conventional pn junction diodes, and its reverse breakdown voltage is also not large. Also, the Schottky barrier diode is pn
They also have the disadvantage that the maximum allowable junction temperature is lower than that of junction diodes, requiring special consideration to improve heat dissipation. An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and provide a new pn junction diode that has low loss, high speed, and high reliability.

A method of manufacturing a diode according to an embodiment of the present invention will be described below with reference to FIG. First, add antimony 3× as an impurity.
1018at0mS/Thickness 200Itm including CliL (
7) On the n+ type substrate 11, 1×101 phosphorus is added as an impurity.
5at0ms/(thickness 8μMf including -d) n-type base layer 12 is formed by vapor phase epitaxy (a).

Next, boron was deposited on the surface of the n-type base layer 12 at 5×10 18 at0 ms/CTL by vapor phase growth using trichlorosilane containing diborane at 900° C. for 60 minutes to a thickness of 25
μm(7) p-type polycrystalline layer 13 is formed.

1 At this time, boron is released from the p-type polycrystalline layer 13 simultaneously with the formation of the p-type polycrystalline layer 13.

Diffused into the mold base layer 12, the impurity concentration is 1X1017
At 0 ms/d and a thickness of 0.05 μm (7) a p-type single crystal layer 14 is formed (b). Next, phosphorus is diffused on the exposed main surface of the n+ type substrate 11 at 9000 C1 for 30 minutes to form an impurity concentration of 1×1020 at0 ms/CTL and a thickness of 1 μM On+10 type single crystal layer 15 (c). Next, the Cr layer 16 is formed to a thickness of 0.1 μm using a vacuum evaporation method, and the Ni layer 17 is formed to a thickness of 0.1 μm.
The Ag layer 18 is formed to a thickness of 8 μm and the Ag layer 18 is formed to a thickness of 21.6 μm on both sides of the p-type polycrystalline layer 13 and the n + type single-crystalline layer 15 (
d).

Next, the pellets are pelletized into beveled pellets by a sand cut method, and the end faces of the pellets, including the exposed ends of the Pn junction, are coated with silicone rubber 19.

Next, the main electrode 21 is attached on the electrode layers 16 to 18 on the p-type polycrystalline layer 13 side via the solder layer 20, and the diode is completed (e).

Such diodes are typically used sealed in metal cans. In the case of in-situ 5, the electrode layers 16 to 18 on the side of the n+ type single crystal layer 15 are bonded to the bottom of the metal can via a solder layer, and this metal can becomes the other main electrode. An important point in the structure of the present invention is how to control the impurity concentration α of the p-type polycrystalline layer 13.

FIG. 2 is a diagram showing the potential drop at various parts when a forward current is applied to the diode of the present invention, and the forward potential drop VF of the diode with this structure is expressed as follows. Here, Vc: Contact drop between the p-type polycrystalline layer 13 and the electrode layers 16 to 1 Vp+: Potential drop within the p-type polycrystalline layer 13 VJ: Potential drop at the junction and within the n-type base layer 12 Sum of potential drops VN+: Potential drop Vσ within the n+ type substrate 11; Contact drop between the n+ single crystal layer 25 and the electrode layers 16 to 18.

Here, the impurity concentration α of the p-type polycrystalline layer 13 influences three items: VCVP+VJ.

Therefore, the value of α should be selected so as to minimize the sum of C, Vp+, and J. This point will be explained below. FIG. 3 is a diagram showing the relationship between α, Vc, and Vp+ obtained through experiments by the inventors. In general, polycrystalline semiconductor layers have good contact with metal, but the impurity concentration is 1018at0ms.
/ below, the contact drop Vc increases rapidly. On the other hand, the potential drop Vp+ within the p-type polycrystalline layer 13 also increases as the impurity concentration α decreases. On the other hand, the thickness of the n-type base layer 12 is set to 30 μm or less, and the total amount of impurities Q of the p-type single crystal layer 14 is set to 1011 to 1014at0m.
The present inventors have already proposed that low loss and high speed of the diode can be achieved at the same time by using s/d (Japanese Patent Application No. 50-93109).

As stated therein, when Q is lowered, the sum VJ of the potential drop at the junction and the potential drop within the n-type base layer 12 becomes smaller. Therefore, as α becomes smaller, Q also becomes smaller, so V
J decreases. Curve a in FIG. 4 shows this. If we calculate the sum of C, VP+, and VJ from curves a in Figures 3 and 4, we get curve b in Figure 4, and α is 5×
It can be seen that it is most preferable to select a value in the vicinity of 1018at0Ins/. Next, in order to reduce N+, it is necessary to increase the impurity concentration of the n+ type substrate 11.

However, if the impurity concentration of the n+ type substrate 11 is made too high, the n type impurity will diffuse from the n+ type substrate 11 into the n type base layer 12, and the reverse breakdown voltage of the diode will decrease. For example, the upper limit of the impurity concentration of the n+ type substrate 21 to obtain a breakdown voltage of 150 V is 3×10 18 at0 ms/~. By the way 3
At an impurity concentration of ×1018at0ms/CTil, contact with electrode layers 16 to 18 and drop Vσ are 0.0.
It cannot be lower than 1. Therefore, in order to reduce Vσ, it is necessary to newly form an n+ type semiconductor single crystal layer 15 on the surface of the n+ type substrate 21. n+10 type single crystal layer 1
The impurity concentration of 5 is required to be 1019 at0 ms/~ or more. Cr is preferable as the metal for the pair of ohmic contact electrodes, and Nl and Nl are used in the second and third layers, respectively.
By selecting Ag, it is possible to form multilayer electrode layers 16 to 18 that can be soldered to external lead terminals.

By using these electrode layers, an n+ type single crystal layer, and an n+ type substrate, the sum of VN+ and Vσ can be made 0.02 or less, so the total VF can be made 0.8V or less. can.

As described above, according to the structure of the present invention, the forward potential drop of the diode can be reduced to 0.8 V or less, which is the average value of the forward potential drop of the conventional gold diffusion type high-speed diode. , it has become possible to significantly reduce the voltage compared to 2V.

Next, it will be explained that the element of the present invention has reverse breakdown voltage and reliability equivalent to that of a conventional Pn junction diode.

As already mentioned, the forward potential drop of the diode can be reduced by reducing the total amount of impurities Q in the p-type single crystal layer 14, but in order to reduce Q, the thickness of the p-type single crystal layer is reduced. There is a need. If the thickness of this layer is reduced, Pn
The bonding surface is affected by the thermal strain of the multilayer electrode layer on the surface, which causes a decrease in breakdown voltage.
Since the type single crystal layer 14 is separated from the electrode layers 16, 17, and 18 by the thick p-type polycrystalline layer 13, it is not affected by the strain of the multilayer electrode layer, and sufficient reverse breakdown voltage characteristics can be obtained. can. In addition, the silicone rubber 19 that protects the Pn joint end face must be
A thickness of 0.01 tm or more is required.

In order to reduce Q, when the p-type single crystal layer is thinned and the p-type polycrystalline layer 13 is not present, the thickness of the silicone comb at the exposed end of the Pn junction is reduced as shown in FIG. 5a. SaD
is as thin as about 1 to 2 μm, making it impossible to obtain sufficient withstand voltage. In contrast, the structure according to the present invention has a thickness of 25 μM.
O) Due to the presence of the p-type polycrystalline layer 13, the thickness D of the silicone rubber at the joint end face is approximately 15 μm (FIG. 5b), making it possible to obtain a sufficient withstand voltage. In order to obtain a breakdown voltage, the thickness of the p-type polycrystalline layer 13 is preferably 15 μm or more. As described above, according to the present invention, it is possible to obtain reverse breakdown voltage and reliability equivalent to those of conventional Pn junction diodes.

The reverse breakdown voltage of the prototype diode is 150V, the forward potential drop is 0.78V at a forward current of 30A, and the reverse recovery time is 80V.
nsec, making it possible to simultaneously achieve low loss and high speed while maintaining the same level of reverse breakdown voltage as conventional Pn junctions.

As described above in detail, the present invention is effective in obtaining a Pn junction diode having low loss, high speed, and high reliability.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a diode according to an embodiment of the present invention and its main manufacturing process, Fig. 2 is an explanatory diagram showing the forward potential drop of each part of the diode of the present invention, and Fig. 3 is a diagram showing the impurity concentration of the p-type polycrystalline layer. Figure 4 shows the relationship between α, Vc, and p+.
FIG. 5 is a diagram showing the state of silicone rubber coating on the end face of the pellet of the present invention diode (b) in the case (a) where no p-type polycrystalline layer is present. .

Claims (1)

[Claims] 1 a first silicon single crystal layer having an n-type conductivity type; a second silicon single crystal layer having an n-type conductivity type adjacent to one surface of the first silicon single crystal layer and having a higher impurity concentration; , a third silicon single crystal layer of n-type conductivity type having a thickness of 30 μm or less and having a lower impurity concentration adjacent to the other surface of the first silicon single crystal layer; and adjacent to the third silicon single crystal layer. to form a pn junction with the third silicon single crystal, and 10^1^1 to 10^1^4 atoms/
A fourth silicon single crystal layer of p-type conductivity type having a total amount of impurities of cm^2 and a layer adjacent to the fourth silicon single crystal layer serving as a diffusion source of p-type impurities to this layer are 5×10^1^8at.
A silicon polycrystalline layer having an impurity concentration near oms/cm^3, a second silicon single crystal layer, and a silicon polycrystalline layer formed on the surfaces of the silicon polycrystalline layer and the first silicon layer in order from the silicon layer side.
A semiconductor rectifier comprising: a multilayer ohmic electrode layer consisting of a layer of Cr, a second layer of Ni, and a third layer of Ag; and silicone rubber covering at least an exposed end of a pn junction.