JPH06177365A - Schottky barrier diode - Google Patents

Abstract

PURPOSE:To dissolve troubles with regard to a P-N junction diode and a Schottky-junction diode and to provide a high breakdown voltage, high speed switching and low noise Schottky barrier diode. CONSTITUTION:A Schottky barrier diode is constituted into such a structure that P-N junctions J and Schottky junctions are alternately arranged on one surface of an N-type semiconductor substrate 1 and the P-N junctions, which are adjoined each other at the time of zero bias directly under the Schottky junctions, are overlapped with each other by a depletion layer and at the same time, the impurity concentration of an N-type semiconductor layer (a second epitaxial layer) 7 forming the Schottky junctions is made lower than that of an N-type internal semiconductor layer (a first epitaxial layer) 2 and the layer 7 is formed into a high-resistance layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Schottky barrier diode structure having high speed switching and low noise.

[0002]

As is well known, various characteristics of Schottky barrier diodes have been developed and various Schottky barrier diodes have been proposed in order to improve the characteristics of the Schottky barrier diode, in particular, the characteristics of switching speed, forward direction and reverse direction.

FIG. 1 was first proposed by the applicant of the present application (Japanese Patent Application No. 4-
58394) and 1 is an N-type semiconductor substrate,
Reference numeral 2 is an N-type semiconductor layer laminated on the substrate 1 by an epitaxial growth method or the like, and 3 is a P + region in which a gap W is provided in the N-layer 2 and arranged in stripes, whereby a PN junction J is formed. To do. 4 is a Schottky barrier metal (eg Mo, Cr, Al, etc.) that forms a Schottky junction with the N − layer 2, 5
Is an electrode metal (such as Al) provided over the P + region 3 and the Schottky barrier metal 4, and 6 is an electrode metal provided on the other surface of the semiconductor substrate. The electrode metal 5 may be the same as the shovel (2) toki barrier metal.

In the above structure, when the width W or the area of the Schottky junction is made extremely small, the reverse current becomes close to the value of the PN junction, and the injected carrier is very small and the same positive value as that of the PN junction. Directional characteristics are obtained, and the reverse recovery time is much shorter than that of the PN junction. Incidentally, FIG. 2 is a partially enlarged view for explaining the epitaxial layer 2 of FIG.
Impurity concentration of 9 × 10 ¹⁴ Atoms / cm3 (ρ = 5Ω · cm)
When using, the depletion layer width (at zero bias) is about 0.
It is 8 μm. The PN junction is 3 μm deep from the surface,
When the P + regions 3 in which the side surface of the P + portion 3 is substantially right-angled are provided with an interval W (Schottky junction width) of about 1.5 μm and arranged, as described above, at the time of zero bias, P + region 3 is formed.
A depletion layer of about 0.8 μm extends from the N junction to the N − side, the depletion layers overlap each other, and the channel region sandwiched between the Schottky portion and the PN junctions on both sides is substantially depleted.

FIG. 3 is a VR-JR (reverse voltage-reverse leakage current) characteristic diagram of the diode, and FIG. 4 is a VF-JF of the diode.
(Forward voltage drop-Forward current) characteristic diagram, FIG. 5 shows nSec-Vs
FIG. 9 is a characteristic diagram of age (time-surge voltage).

As shown in FIG. 3 (a), the reverse characteristic of the conventional structure is such that the reverse leakage current JR is suppressed to about -10 ^-5 Amp / cm 2 and the conventional Schottky barrier diode JR is used.
Is about 10 ⁻³ Amp / cm 2, it is known that the characteristics are very close to the reverse leakage current value of the PN junction. As for the forward characteristic, as shown in FIG. 4 (a), VF of 0.9 volt is obtained when the forward current density JF = 150 Amp / cm2, and VF of the PN junction diode is 1.1.
It is a desirable value compared to ~ 1.3 volt. As for the switching characteristics, when the load is an L load (1 μH), as shown in FIG. 5A, after switching in the reverse direction, ringing occurs in resonance with C and L in the circuit. The lower the peak value Vsurge of the first resonance waveform is, the more desirable. (3) In the conventional structure example, Vsurge = 180V is shown.

[0007]

However, in the prior art, the width W is extremely narrow in order to obtain excellent characteristics industrially. (W
≦ 2.0 μm) In addition, controllability with high accuracy is required, which is a problem in manufacturing technology.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems of the conventional PN junction type and Schottky junction type diodes, and to provide a diode with high breakdown voltage, high speed and low noise.

[0009]

According to the present invention, PN junctions and Schottky junctions are alternately arranged on one surface of an N-type semiconductor substrate, and adjacent PN junctions immediately below a Schottky junction overlap with a depletion layer at zero bias. The N-type semiconductor layer (second epi layer) forming the Schottky junction has a lower impurity concentration than the internal N-type semiconductor layer (first epi layer).

[0010]

FIG. 6 is a structural view of an embodiment of the present invention, and FIG. 7 is a partially enlarged view for explaining the present invention. The present invention shows that N
And a high resistance N-- layer 7 (second epitaxial layer) having a lower impurity concentration than the N-- layer 2 (first epitaxial layer) formed on the semiconductor substrate 1. A Schottky junction is formed with the N--layer. As is well known, when the voltage V is applied in the opposite direction, the thickness Wo of the depletion layer is

[0011]

[Equation 1]

(4) It is expressed by the above equation 1. That is, it is shown that the lower the impurity concentration N0, the larger the depletion layer W0. This is because in the conventional structure, when the width W of the Schottky junction or the area thereof is reduced, the flow approaches the reverse flow of the PN junction because the depletion layer of the PN junction is formed directly below the Schottky junction from two sides. That is, the greater the overlapping degree of the depletion layers, the closer to the reverse flow of the PN junction. As described above, lowering the N-type impurity concentration immediately below the Schottky junction means that the width of the depletion layer formed increases and the degree of overlap increases with the same applied voltage. Therefore, if the Schottky metal of FIG. 7 has the same width W or area, the PN junction of the structure of FIG. 7 is closer to the reverse flow than the structure of FIG. Further, if the backflow is the same, the width W or area of the Schottky junction of the structure of FIG. 7 may be made larger than that of FIG. This has a great advantage in facilitating the processing process.

The structure of the present invention has an N type of 10 Ω · cm (NB =
The thickness of about 2.5 μm of the second epitaxial layer 7 of 4.5 × 10 ¹⁴ Atows / cm 3) is set to the first epitaxial layer 2, 5Ω.
・ Double epitaxial silicon wafer pre-deposited on cm (NB = 1 × 10 ¹⁵ Atows / cm 3) 12 μm thick
Was used. The P + region 3 was formed by ion implantation or trench etching followed by P + diffusion to form a shape substantially as shown in FIG. The Schottky width W is 2.
It was 5 μm. After that, ohmic contact with AL and P +,
N-- was vapor-deposited so as to be in Schottky contact with the main anodic electron A, and the ohmic metal B was provided on the N + surface to complete the diode.

The characteristics of the embodiment of the present invention are shown in FIGS.
As shown in (b) of FIG.
The characteristics are similar to those of the junction and are improved, but the forward characteristics are slightly worse in the structure of the present invention than in the conventional structure. However, the noise during switching was smaller in the structure of the present invention than that in the conventional structure, and a value excellent in Vsurge = 160V was obtained. (5)

[0015]

According to the present invention, a high speed, low noise diode
Can be provided. Also, a structure similar to that of the conventional example can be manufactured by an easy processing process. It should be noted that there is no great difference in the characteristics of the epitaxial layer 7 even if it is above or slightly below the lower end of the P + layer.

[Brief description of drawings]

FIG. 1 Conventional structure diagram

FIG. 2 is a partially enlarged view for explaining FIG.

[Fig.3] VR-JR (reverse voltage-reverse leakage current) characteristic diagram of diode

[Figure 4] Diode VF-JF (forward voltage drop-forward current)
Characteristic diagram

FIG. 5: nSec-Vsuge (time-surge voltage) characteristic diagram

FIG. 6 is a structural diagram of an embodiment of the present invention.

FIG. 7 is a partially enlarged view for explaining FIG. 6;

[Explanation of symbols]

 1 N-type semiconductor substrate 2 N- type semiconductor layer (first epitaxial layer) 3 P + region 4 Schottky barrier metal 5 Electrode metal 6 Electrode metal 7 N-- type semiconductor layer (second epitaxial layer) (6) W Schottky Width

Claims (1)

[Claims] 1. An N-type first epitaxial layer and a second epitaxial layer are laminated on an N-type semiconductor substrate, and a PN junction and a Schottky junction are alternately arranged on one surface of the second epitaxial layer, In addition, the PN junction adjacent to the Schottky junction immediately under zero bias is configured to overlap the depletion layer, and the impurity concentration of the second epitaxial layer forming the Schottky junction is lower than the impurity concentration of the first epitaxial layer. A Schottky barrier diode characterized in that